Publications by authors named "Gavin W Halbert"

24 Publications

  • Page 1 of 1

Crystal Structure and Twisted Aggregates of Oxcarbazepine Form III.

Cryst Growth Des 2022 Jul 24;22(7):4146-4156. Epub 2022 May 24.

EPSRC Future CMAC Research Hub, University of Strathclyde, Glasgow G1 1RD, U.K.

Polymorphism and crystal habit play vital roles in dictating the properties of crystalline materials. Here, the structure and properties of oxcarbazepine (OXCBZ) form III are reported along with the occurrence of twisted crystalline aggregates of this metastable polymorph. OXCBZ III can be produced by crystallization from the vapor phase and by recrystallization from solution. The crystallization process used to obtain OXCBZ III is found to affect the pitch, with the most prominent effect observed from the sublimation-grown OXCBZ III material where the pitch increases as the length of aggregates increases. Sublimation-grown OXCBZ III follows an unconventional mechanism of formation with condensed droplet formation and coalescence preceding nucleation and growth of aggregates. A crystal structure determination of OXCBZ III from powder X-ray diffraction methods, assisted by crystal structure prediction (CSP), reveals that OXCBZ III, similar to carbamazepine form II, contains void channels in its structure with the channels, aligned along the crystallographic axis, oriented parallel to the twist axis of the aggregates. The likely role of structural misalignment at the lattice or nanoscale is explored by considering the role of molecular and closely related structural impurities informed by crystal structure prediction.
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http://dx.doi.org/10.1021/acs.cgd.2c00152DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9337787PMC
July 2022

Small scale in vitro method to determine a potential bioequivalent equilibrium solubility range for fed human intestinal fluid.

Eur J Pharm Biopharm 2022 Aug 16;177:126-134. Epub 2022 Jun 16.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom. Electronic address:

Intestinal drug solubility is a key parameter controlling oral absorption but varies both intra and inter individuals and between the fasted and fed states, with food intake known to alter the bioavailability of many compounds. Intestinal solubility can be measured in vitro either using sampled fed human intestinal fluid (FeHIF) or simulated fed intestinal fluid (SIF) but neither approach is optimal. FeHIF is difficult to obtain and variable, whilst for fed SIF multiple recipes are available with no consensus on the ideal version. A recent study characterised FeHIF aspirates using a multidimensional approach and calculated nine simulated media recipes that covered over ninety percent of FeHIF compositional variability. In this study the equilibrium solubility of thirteen drugs have been measured using the nine simulated media recipes and compared to multiple previous design of experiment (DoE) studies, which have examined the impact of fed SIF media components on solubility. The measured nine media solubility data set is only statistically equivalent to the large scale 92 media DoE in 4 out of 13 drug comparisons, but has improved equivalence against small scale DoEs (9 or 10 media) with 6 out of 9 or 10 out of 12 (9 and 10 media respectively) equivalent. Selective removal of non-biorelevant compositions from the 92 media DoE improves statistical equivalence to 9 out of 13 comparisons. The results indicate that solubility equivalence is linked to media component concentrations and compositions, the nine media system is measuring a similar solubility space to previous systems, with a narrower solubility range than the 92 point DoE but equivalent to smaller DoE systems. Phenytoin and tadalafil display a narrow solubility range, a behaviour consistent with previous studies in fed and fasted states and only revealed through the multiple media approach. Custom DoE analysis of the nine media results to determine the most statistically significant component influencing solubility does not detect significant components. Indicating that the approach has a low statistical resolution and is not appropriate if determination of media component significance is required. This study demonstrates that it is possible to assess the fed intestinal equilibrium solubility envelope using the nine media recipes obtained from a multi-dimensional analysis of fed HIF. The derivation of the nine media compositions coupled with the results in this study indicate that the solubility results are more likely to reflect the fed intestinal solubility envelope than previous DoE studies and highlight that the system is worthy of further investigation.
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http://dx.doi.org/10.1016/j.ejpb.2022.06.005DOI Listing
August 2022

Structured solubility behaviour in bioequivalent fasted simulated intestinal fluids.

Eur J Pharm Biopharm 2022 Jul 20;176:108-121. Epub 2022 May 20.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom. Electronic address:

Drug solubility in intestinal fluid is a key parameter controlling absorption after the administration of a solid oral dosage form. To measure solubility in vitro simulated intestinal fluids have been developed, but there are multiple recipes and the optimum is unknown. This situation creates difficulties during drug discovery and development research. A recent study characterised sampled fasted intestinal fluids using a multidimensional approach to derive nine bioequivalent fasted intestinal media that covered over 90% of the compositional variability. These media have been applied in this study to examine the equilibrium solubility of twenty one exemplar drugs (naproxen, indomethacin, phenytoin, zafirlukast, piroxicam, ibuprofen, mefenamic acid, furosemide, aprepitant, carvedilol, tadalafil, dipyridamole, posaconazole, atazanavir, fenofibrate, felodipine, griseofulvin, probucol, paracetamol, acyclovir and carbamazepine) to determine if consistent solubility behaviour was present. The bioequivalent media provide in the majority of cases structured solubility behaviour that is consistent with physicochemical properties and previous solubility studies. For the acidic drugs (pKa < 6.3) solubility is controlled by media pH, the profile is identical and consistent and the lowest and highest pH media identify the lowest and highest solubility in over 70% of cases. For weakly acidic (pKa > 8), basic and neutral drugs solubility is controlled by a combination of media pH and total amphiphile concentration (TAC), a consistent solubility behaviour is evident but with variation related to individual drug interactions within the media. The lowest and highest pH × TAC media identify the lowest and highest solubility in over 78% of cases. A subset of the latter category consisting of neutral and drugs non-ionised in the media pH range have been identified with a very narrow solubility range, indicating that the impact of the simulated intestinal media on their solubility is minimal. Two drugs probucol and atazanavir exhibit unusual behaviour. The study indicates that the use of two appropriate bioequivalent fasted intestinal media from the nine will identify in vitro the maximum and minimum solubility boundaries for drugs and due to the media derivation this is probably applicable in vivo. These media could be applied during discovery and development activities to provide a solubility range, which would assist placement of the drug within the BCS/DCS and rationalise drug and formulation decisions.
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http://dx.doi.org/10.1016/j.ejpb.2022.05.010DOI Listing
July 2022

Mefenamic acid solid dispersions: Impact of formulation composition on processing parameters, product properties and performance.

Int J Pharm 2022 Mar 24;616:121505. Epub 2022 Jan 24.

EPSRC Future Manufacturing Research Hub in Continuous Manufacturing and Advanced Crystallisation, University of Strathclyde, Technology and Innovation Centre, 99 George Street, Glasgow G1 1RD, UK; Strathclyde Institute for Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.

The objective of this study was to develop an immediate release (IR), crystalline solid dispersion (CSD) formulation of Mefenamic acid (MFA) by hot-melt-extrusion (HME) and assess the impact of drug loading on process parameters, product physico-chemical properties and product performance. An HME process to produce a range of MFA-Soluplus®-Sorbitol polymer matrix CSD formulations was developed based on rheological screening assays of physical mixtures (PM). The impact of drug loading on process parameters was compared to the impact of drug loading on the physico-chemical properties of formulations. Based on process and product data, three groupings of API drug loading were identified: sub-saturated, saturated, and supersaturated systems. CSD formulations were obtained for 20-50% (w/w) drug loading containing the stable polymorphic form I of MFA. CSD formulations predominantly improved the consistency of the product performance. An Amorphous Solid Dispersion (ASD) was obtained for 10% (w/w) drug loading, exhibiting faster drug release even at physiologically relevant pH. This study illustrates the impact of drug loading on process and product characteristics and how a better understanding of maximum API solubility in a given polymer system can improve targeted formulation development.
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http://dx.doi.org/10.1016/j.ijpharm.2022.121505DOI Listing
March 2022

Fasted intestinal solubility limits and distributions applied to the biopharmaceutics and developability classification systems.

Eur J Pharm Biopharm 2022 Jan 16;170:160-169. Epub 2021 Dec 16.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom. Electronic address:

After oral administration, a drug's solubility in intestinal fluid is an important parameter influencing bioavailability and if the value is known it can be applied to estimate multiple biopharmaceutical parameters including the solubility limited absorbable dose. Current in vitro measurements may utilise fasted human intestinal fluid (HIF) or simulated intestinal fluid (SIF) to provide an intestinal solubility value. This single point value is limited since its position in relation to the fasted intestinal solubility envelope is unknown. In this study we have applied a nine point fasted equilibrium solubility determination in SIF, based on a multi-dimensional analysis of fasted human intestinal fluid composition, to seven drugs that were previously utilised to investigate the developability classification system (ibuprofen, mefenamic acid, furosemide, dipyridamole, griseofulvin, paracetamol and acyclovir). The resulting fasted equilibrium solubility envelope encompasses literature solubility values in both HIF and SIF indicating that it measures the same solubility space as current approaches with solubility behaviour consistent with previous SIF design of experiment studies. In addition, it identifies that three drugs (griseofulvin, paracetamol and acyclovir) have a very narrow solubility range, a feature that single point solubility approaches would miss. The measured mid-point solubility value is statistically equivalent to the value determined with the original fasted simulated intestinal fluid recipe, further indicating similarity and that existing literature results could be utilised as a direct comparison. Since the multi-dimensional approach covered greater than ninety percent of the variability in fasted intestinal fluid composition, the measured maximum and minimum equilibrium solubility values should represent the extremes of fasted intestinal solubility and provide a range. The seven drugs all display different solubility ranges and behaviours, a result also consistent with previous studies. The dose/solubility ratio for each measurement point can be plotted using the developability classification system to highlight individual drug behaviours. The lowest solubility represents a worst-case scenario which may be useful in risk-based quality by design biopharmaceutical calculations than the mid-point value. The method also permits a dose/solubility ratio frequency distribution determination for the solubility envelope which permits further risk-based refinement, especially where the drug crosses a classification boundary. This novel approach therefore provides greater in vitro detail with respect to possible biopharmaceutical performance in vivo and an improved ability to apply risk-based analysis to biopharmaceutical performance. Further studies will be required to expand the number of drugs measured and link the in vitro measurements to in vivo results.
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http://dx.doi.org/10.1016/j.ejpb.2021.12.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8769049PMC
January 2022

Small scale in vitro method to determine a bioequivalent equilibrium solubility range for fasted human intestinal fluid.

Eur J Pharm Biopharm 2021 Nov 20;168:90-96. Epub 2021 Aug 20.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom. Electronic address:

Drug solubility is a key parameter controlling oral absorption, but intestinal solubility is difficult to assess in vitro. Human intestinal fluid (HIF) aspirates can be applied but they are variable, difficult to obtain and expensive. Simulated intestinal fluids (SIF) are a useful surrogate but multiple recipes are available and the optimum is unknown. A recent study characterised fasted HIF aspirates using a multi-dimensional approach and determined nine bioequivalent SIF media recipes that represented over ninety percent of HIF compositional variability. In this study these recipes have been applied to determine the equilibrium solubility of twelve drugs (naproxen, indomethacin, phenytoin, piroxicam, aprepitant, carvedilol, zafirlukast, tadalafil, fenofibrate, griseofulvin, felodipine, probucol) previously investigated using a statistical design of experiment (DoE) approach. The bioequivalent solubility measurements are statistically equivalent to the previous DoE, enclose literature solubility values in both fasted HIF and SIF, and the solubility range is less than the previous DoE. These results indicate that the system is measuring the same solubility space as literature systems with the lower overall range suggesting improved equivalence to in vivo solubility, when compared to DoEs. Three drugs (phenytoin, tadalafil and griseofulvin) display a comparatively narrow solubility range, a behaviour that is consistent with previous studies and related to the drugs' molecular structure and properties. This solubility behaviour would not be evident with single point solubility measurements. The solubility results can be analysed using a custom DoE to determine the most statistically significant factor within the media influencing solubility. This approach has a lower statistical resolution than a formal DoE and is not appropriate if determination of media factor significance for solubilisation is required. This study demonstrates that it is possible to assess the fasted intestinal equilibrium solubility envelope using a small number of bioequivalent media recipes obtained from a multi-dimensional analysis of fasted HIF. The derivation of the nine bioequivalent SIF media coupled with the lower measured solubility range indicate that the solubility results are more likely to reflect the fasted intestinal solubility envelope than previous DoE studies and highlight that intestinal solubility is a range and not a single value.
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http://dx.doi.org/10.1016/j.ejpb.2021.08.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8491656PMC
November 2021

Manufacturing Considerations for the Development of Lipid Nanoparticles Using Microfluidics.

Pharmaceutics 2020 Nov 15;12(11). Epub 2020 Nov 15.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.

In the recent of years, the use of lipid nanoparticles (LNPs) for RNA delivery has gained considerable attention, with a large number in the clinical pipeline as vaccine candidates or to treat a wide range of diseases. Microfluidics offers considerable advantages for their manufacture due to its scalability, reproducibility and fast preparation. Thus, in this study, we have evaluated operating and formulation parameters to be considered when developing LNPs. Among them, the flow rate ratio (FRR) and the total flow rate (TFR) have been shown to significantly influence the physicochemical characteristics of the produced particles. In particular, increasing the TFR or increasing the FRR decreased the particle size. The amino lipid choice (cationic-DOTAP and DDAB; ionisable-MC3), buffer choice (citrate buffer pH 6 or TRIS pH 7.4) and type of nucleic acid payload (PolyA, ssDNA or mRNA) have also been shown to have an impact on the characteristics of these LNPs. LNPs were shown to have a high (>90%) loading in all cases and were below 100 nm with a low polydispersity index (≤0.25). The results within this paper could be used as a guide for the development and scalable manufacture of LNP systems using microfluidics.
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http://dx.doi.org/10.3390/pharmaceutics12111095DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7697682PMC
November 2020

Improving Consistency for a Mefenamic Acid Immediate Release Formulation.

J Pharm Sci 2020 11 25;109(11):3462-3470. Epub 2020 Aug 25.

EPSRC Future Manufacturing Research Hub, University of Strathclyde, Technology and Innovation Centre, 99 George Street, Glasgow G1 1RD, UK; Strathclyde Institute for Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, UK.

The objective of this study was to develop an immediate release dose form containing 250 mg Mefenamic acid (MFA) presented as a crystalline solid dispersion in order to achieve improved consistency in drug release through a simplified formulation compared to a commercial product. An MFA-Soluplus®-Sorbitol polymer matrix was developed using an HME process based on rheological screening assays of physical mixtures. The physico-chemical properties of these formulations were assessed by thermal analysis, FTIR, mechanical testing and SEM image analysis, confirming the crystalline character and stable polymorphic form I of the API in the polymer matrix. A faster release and a significant improvement in consistency (±6%) of drug release was observed compared to a commercially available MFA product (±17%) (250 mg capsule). This study illustrates advantages of applying a structured development program aimed at retaining API physical properties in the final dosage form.
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http://dx.doi.org/10.1016/j.xphs.2020.08.012DOI Listing
November 2020

Rapid scale-up and production of active-loaded PEGylated liposomes.

Int J Pharm 2020 Aug 2;586:119566. Epub 2020 Jul 2.

Strathclyde Institute of Pharmacy and Biomedical Sciences, 161 Cathedral Street, University of Strathclyde, Glasgow, Scotland G4 0RE, UK. Electronic address:

Manufacturing of liposomal nanomedicines (e.g. Doxil®/Caelyx®) is a challenging and slow process based on multiple-vessel and batch processing techniques. As a result, the translation of these nanomedicines from bench to bedside has been limited. Microfluidic-based manufacturing offers the opportunity to address this issue, and de-risk the wider adoption of nanomedicines. Here we demonstrate the applicability of microfluidics for continuous manufacturing of PEGylated liposomes encapsulating ammonium sulfate (250 mM). Doxorubicin was subsequently active-loaded into these pre-formed liposomes. Critical process parameters and material considerations demonstrated to influence the liposomal product attributes included solvent selection and lipid concentration, flow rate ratio, and temperature and duration used for drug loading. However, the total flow rate did not affect the liposome product characteristics, allowing high production speeds to be adopted. The final liposomal product comprised of 80-100 nm vesicles (PDI < 0.2) encapsulating ≥ 90% doxorubicin, with matching release profiles to the innovator product and is stable for at least 6 months. Additionally, vincristine and acridine orange were active-loaded into these PEGylated liposomes (≥ 90% and ~100 nm in size) using the same process. These results demonstrate the ability to produce active-loaded PEGylated liposomes with high encapsulation efficiencies and particle sizes which support tumour targeting.
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http://dx.doi.org/10.1016/j.ijpharm.2020.119566DOI Listing
August 2020

Use of Terahertz-Raman Spectroscopy to Determine Solubility of the Crystalline Active Pharmaceutical Ingredient in Polymeric Matrices during Hot Melt Extrusion.

Mol Pharm 2019 10 9;16(10):4361-4371. Epub 2019 Sep 9.

EPSRC Future Manufacturing Research Hub, CMAC , University of Strathclyde, Technology and Innovation Centre , 99 George Street , Glasgow G1 1RD , U.K.

Polymer-based amorphous solid dispersions (ASDs) comprise one of the most promising formulation strategies devised to improve the oral bioavailability of poorly water-soluble drugs. Exploitation of such systems in marketed products has been limited because of poor understanding of physical stability. The internal disordered structure and increased free energy provide a thermodynamic driving force for phase separation and recrystallization, which can compromise therapeutic efficacy and limit product shelf life. A primary concern in the development of stable ASDs is the solubility of the drug in the polymeric carrier, but there is a scarcity of reliable analytical techniques for its determination. In this work, terahertz (THz) Raman spectroscopy was introduced as a novel empirical approach to determine the saturated solubility of crystalline active pharmaceutical ingredient (API) in polymeric matrices directly during hot melt extrusion. The solubility of a model compound, paracetamol, in two polymer systems, Affinisol 15LV (HPMC) and Plasdone S630 (copovidone), was determined by monitoring the API structural phase transitions from crystalline to amorphous as an excess of crystalline drug dissolved in the polymeric matrix. THz-Raman results enabled construction of solubility phase diagrams and highlighted significant differences in the solubilization capacity of the two polymer systems. The maximum stable API-load was 20 wt % for Affinisol 15LV and 40 wt % for Plasdone S630. Differential scanning calorimetry and XRPD studies corroborated these results. This approach has demonstrated a novel capability to provide real-time API-polymer phase equilibria data in a manufacturing relevant environment and promising potential to predict solid-state solubility and physical stability of ASDs.
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http://dx.doi.org/10.1021/acs.molpharmaceut.9b00703DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6785800PMC
October 2019

Topography of Simulated Intestinal Equilibrium Solubility.

Mol Pharm 2019 05 16;16(5):1890-1905. Epub 2019 Apr 16.

Strathclyde Institute of Pharmacy and Biomedical Sciences , University of Strathclyde , 161 Cathedral Street , Glasgow G4 0RE , United Kingdom.

Oral administration of a solid dosage form requires drug dissolution in the gastrointestinal tract before absorption. Solubility is a key factor controlling dissolution, and it is recognized that, within the intestinal tract, this is influenced by the luminal fluid pH, amphiphile content, and composition. Various simulated intestinal fluid recipes have been introduced to mimic this behavior and studied using a range of different experimental techniques. In this article, we have measured equilibrium solubility utilizing a novel four component mixture design (4CMD) with biorelevant amphiphiles (bile salt, phospholipid, oleate, and monoglyceride) within a matrix of three pH values (5, 6, and 7) and total amphiphile concentrations (11.7, 30.6, and 77.5 mM) to provide a topographical and statistical overview. Three poorly soluble drugs representing acidic (indomethacin), basic (carvedilol), and neutral (fenofibrate) categories have been studied. The macroscopic solubility behavior agrees with literature and exhibits an overall increasing solubility from low pH and total amphiphile concentration to high pH and total amphiphile concentration. Within the matrix, all three drugs display different topographies, which can be related to the statistical effect levels of the individual amphiphiles or amphiphile interactions on solubility. The study also identifies previously unreported three and four way factor interactions notably between bile salt, phospholipid, pH, and total amphiphile concentration. In addition, the results also reveal that solubility variability is linked to the number of amphiphiles and the respective ratios in the measurement fluid, with the minimum variation present in systems containing all four amphiphiles. The individual 4CMD experiments within the matrix can be linked to provide a possible intestinal solubility window for each drug that could be applied in PBPK modeling systems. Overall the approach provides a novel overview of intestinal solubility topography along with greater detail on the impact of the various factors studied; however, each matrix requires 351 individual solubility measurements. Further studies will be required to refine the experimental protocol in order the maximize information garnered while minimizing the number of measurements required.
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http://dx.doi.org/10.1021/acs.molpharmaceut.8b01238DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6505523PMC
May 2019

The impact of channel fill level on internal forces during continuous twin screw wet granulation.

Int J Pharm 2019 Mar 28;558:91-100. Epub 2018 Dec 28.

EPSRC Centre for Innovative Manufacturing in Continuous Manufacturing and Crystallisation (CMAC), University of Strathclyde, Technology and Innovation Centre, 99 George Street, G1 1RD Glasgow, United Kingdom; Strathclyde Institute of Pharmacy and Biomedical Sciences (SIPBS), University of Strathclyde, 161 Cathedral Street, G4 0RE Glasgow, United Kingdom. Electronic address:

The forces experienced by the particles inside a twin screw granulator (TSG) are one of the most difficult parameters to measure quantitatively. However, it is possible to perform accurately this measurement through the use of dye containing calibrated microencapsulated sensors (CAMES) whose rupture is directly dependant on their experienced shear stress. The current study measures the extent of local stresses in the transformation from powder to granules at different channel fills during TSG processing. Channel fill has shown good potential as a design tool, however, its validity for predicting particle size distributions has yet to be demonstrated in an 11-mm TSG. The results of this study showed that the particles within the twin screw granulator experienced stresses in the range of 350-1000 kPa and this value was not linear with the specific mechanical energy applied by the granulator. It was observed that the majority of these stresses were produced by material transport processes rather than the granulation in itself. In addition it was determined that the torque required by the TSG increases exponentially after a certain channel fill a feature that requires to be considered in order to design safer, predictable and reliable granulation workspaces.
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http://dx.doi.org/10.1016/j.ijpharm.2018.12.052DOI Listing
March 2019

Influence of Physiological Gastrointestinal Surfactant Ratio on the Equilibrium Solubility of BCS Class II Drugs Investigated Using a Four Component Mixture Design.

Mol Pharm 2017 12 22;14(12):4132-4144. Epub 2017 Aug 22.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde , 161 Cathedral Street, Glasgow G4 0RE, United Kingdom.

The absorption of poorly water-soluble drugs is influenced by the luminal gastrointestinal fluid content and composition, which control solubility. Simulated intestinal fluids have been introduced into dissolution testing including endogenous amphiphiles and digested lipids at physiological levels; however, in vivo individual variation exists in the concentrations of these components, which will alter drug absorption through an effect on solubility. The use of a factorial design of experiment and varying media by introducing different levels of bile, lecithin, and digested lipids has been previously reported, but here we investigate the solubility variation of poorly soluble drugs through more complex biorelevant amphiphile interactions. A four-component mixture design was conducted to understand the solubilization capacity and interactions of bile salt, lecithin, oleate, and monoglyceride with a constant total concentration (11.7 mM) but varying molar ratios. The equilibrium solubility of seven low solubility acidic (zafirlukast), basic (aprepitant, carvedilol), and neutral (fenofibrate, felodipine, griseofulvin, and spironolactone) drugs was investigated. Solubility results are comparable with literature values and also our own previously published design of experiment studies. Results indicate that solubilization is not a sum accumulation of individual amphiphile concentrations, but a drug specific effect through interactions of mixed amphiphile compositions with the drug. This is probably due to a combined interaction of drug characteristics; for example, lipophilicity, molecular shape, and ionization with amphiphile components, which can generate specific drug-micelle affinities. The proportion of each component can have a remarkable influence on solubility with, in some cases, the highest and lowest points close to each other. A single-point solubility measurement in a fixed composition simulated media or human intestinal fluid sample will therefore provide a value without knowledge of the surrounding solubility topography meaning that variability may be overlooked. This study has demonstrated how the amphiphile ratios influence drug solubility and highlights the importance of the envelope of physiological variation when simulating in vivo drug behavior.
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http://dx.doi.org/10.1021/acs.molpharmaceut.7b00354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5717620PMC
December 2017

A novel methodology to study polymodal particle size distributions produced during continuous wet granulation.

Int J Pharm 2017 Mar 16;519(1-2):230-239. Epub 2017 Jan 16.

Strathclyde Institute of Pharmacy and Biomedical Sciences (SIPBS), University of Strathclyde, 161 Cathedral Street, G4 0RE Glasgow, United Kingdom; Medway School of Pharmacy, University of Kent, Medway Campus, Anson Building, Central Avenue, Chatham Maritime, Chatham, Kent, ME4 4TB, United Kingdom. Electronic address:

It is important during powder granulation to obtain particles of a homogeneous size especially in critical situations such as pharmaceutical manufacture. To date, homogeneity of particle size distribution has been defined by the use of the d combined with the span of the particle size distribution, which has been found ineffective for polymodal particle size distributions. This work focuses on demonstrating the limitations of the span parameter to quantify homogeneity and proposes a novel improved metric based on the transformation of a typical particle size distribution curve into a homogeneity factor which can vary from 0 to 100%. The potential of this method as a characterisation tool has been demonstrated through its application to the production of granules using two different materials. The workspace of an 11mm twin screw granulator was defined for two common excipients (α-lactose monohydrate and microcrystalline cellulose). Homogeneity of the obtained granules varied dramatically from 0 to 95% in the same workspace, allowing identification of critical process parameters (e.g. feed rate, liquid/solid ratio, torque velocities). In addition it defined the operational conditions required to produce the most homogeneous product within the range 5μm-2.2mm from both materials.
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http://dx.doi.org/10.1016/j.ijpharm.2017.01.023DOI Listing
March 2017

Statistical investigation of simulated fed intestinal media composition on the equilibrium solubility of oral drugs.

Eur J Pharm Sci 2017 Mar 7;99:95-104. Epub 2016 Dec 7.

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow, G4 0RE, United Kingdom. Electronic address:

Gastrointestinal fluid is a complex milieu and it is recognised that gut drug solubility is different to that observed in simple aqueous buffers. Simulated gastrointestinal media have been developed covering fasted and fed states to facilitate in vitro prediction of gut solubility and product dissolution. However, the combination of bile salts, phospholipids, fatty acids and proteins in an aqueous buffered system creates multiple phases and drug solubility is therefore a complex interaction between these components, which may create unique environments for each API. The impact on solubility can be assessed through a statistical design of experiment (DoE) approach, to determine the influence and relationships between factors. In this paper DoE has been applied to fed simulated gastrointestinal media consisting of eight components (pH, bile salt, lecithin, sodium oleate, monoglyceride, buffer, salt and pancreatin) using a two level D-optimal design with forty-four duplicate measurements and four centre points. The equilibrium solubility of a range of poorly soluble acidic (indomethacin, ibuprofen, phenytoin, valsartan, zafirlukast), basic (aprepitant, carvedilol, tadalafil, bromocriptine) and neutral (fenofibrate, felodipine, probucol, itraconazole) drugs was investigated. Results indicate that the DoE provides equilibrium solubility values that are comparable to literature results for other simulated fed gastrointestinal media systems or human intestinal fluid samples. For acidic drugs the influence of pH predominates but other significant factors related to oleate and bile salt or interactions between them are present. For basic drugs pH, oleate and bile salt have equal significance along with interactions between pH and oleate and lecithin and oleate. Neutral drugs show diverse effects of the media components particularly with regard to oleate, bile salt, pH and lecithin but the presence of monoglyceride, pancreatin and buffer have significant but smaller effects on solubility. There are fourteen significant interactions between factors mainly related to the surfactant components and pH, indicating that the solubility of neutral drugs in fed simulated media is complex. The results also indicate that the equilibrium solubility of each drug can exhibit individualistic behaviour associated with the drug's chemical structure, physicochemical properties and interaction with media components. The utility of DoE for fed simulated media has been demonstrated providing equilibrium solubility values comparable with similar in vitro systems whilst also providing greater information on the influence of media factors and their interactions. The determination of a drug's gastrointestinal solubility envelope provides useful limits that can potentially be applied to in silico modelling and in vivo experiments.
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http://dx.doi.org/10.1016/j.ejps.2016.12.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5312627PMC
March 2017

The gut in the beaker: Missing the surfactants?

Int J Pharm 2016 Nov;514(1):73-80

Capsugel, Encap Drug Delivery, Livingston, EH53 0TH, Scotland, UK.

Gastrointestinal drug administration is the preferred route for the majority of drugs however, the natural physiology and physicochemistry of the gastrointestinal tract is critical to absorption but complex and influenced by factors such as diet or disease. The pharmaceutical sciences drive for product consistency has led to the development of in vitro product performance tests whose utility and interpretation is hindered by the complexity, variability and a lack of understanding. This article explores some of these issues with respect to the drug, formulation and the presence of surfactant excipients and how these interact with the natural bile salt surfactants. Interactions start in the mouth and during swallowing but the stomach and small intestine present the major challenges related to drug dissolution, solubility, the impact of surfactants and supersaturation along with precipitation. The behaviour of lipid based formulations and the influence of surfactant excipients is explored along with the difficulties of translating in vitro results to in vivo performance. Possible future research areas are highlighted with the conclusion that, "a great deal of work using modern methods is still required to clarify the situation".
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http://dx.doi.org/10.1016/j.ijpharm.2016.09.032DOI Listing
November 2016

A novel hot-melt extrusion formulation of albendazole for increasing dissolution properties.

Int J Pharm 2016 Feb 6;499(1-2):175-185. Epub 2016 Jan 6.

EPSRC Centre for Innovative Manufacturing in Continuous Manufacturing and Crystallisation (CMAC), University of Strathclyde, Technology and Innovation Centre, 99 George Street, G1 1RD Glasgow, United Kingdom; Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 161Cathedral Street, G4 0RE Glasgow, United Kingdom.

The main aim of the research focused on the production of hot-melt extrusion (HME) formulations with increased dissolution properties of albendazole (ABZ). Therefore, HME was applied as a continuous manufacturing technique to produce amorphous solid dispersions of the poorly water soluble drug ABZ combined with the polymer matrix polyvinylpyrrolidone PVP K12. HME formulations of ABZ-PVP K12 comprised a drug content of 1%, 5% and 10% w/w. The main analytical characterisation techniques used were scanning electron microscopy (SEM), micro-computed tomography (μ-CT), X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and dissolution profile studies. The application of SEM, XRPD and DSC evidenced drug physical transformation from crystalline to amorphous state and therefore, the achievement of an amorphous solid dispersion. The introduction of a novel technique, μ-CT, to characterise the internal structure of these materials revealed key information regarding materials distribution and void content. Dissolution profile studies evidenced a high increase in drug release profile compared to pure ABZ. These promising results can lead to a great enhancement of the oral bioavailability of ABZ dosage forms. Therefore, HME is a potential continuous manufacturing technique to overcome ABZ poor solubility properties and lead to a significant increase in the therapeutic effect.
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http://dx.doi.org/10.1016/j.ijpharm.2016.01.006DOI Listing
February 2016

Investigation of an 11mm diameter twin screw granulator: Screw element performance and in-line monitoring via image analysis.

Int J Pharm 2015 Dec 15;496(1):24-32. Epub 2015 Sep 15.

Center for Particulate Processes and Products, Purdue University, West Lafayette, IN, USA; School of Chemical Engineering, Purdue University, West Lafayette, IN, USA; Industrial and Physical Pharmacy, Purdue University, West Lafayette, IN, USA. Electronic address:

As twin screw granulation (TSG) provides one with many screw element options, characterization of each screw element is crucial in optimizing the screw configuration in order to obtain desired granule attributes. In this study, the performance of two different screw elements - distributive feed screws and kneading elements - was studied in an 11 mm TSG at different liquid-to-solid (L/S) ratios. The kneading element configuration was found to break large granules more efficiently, leading to narrower granule size distributions. While pharmaceutical industry shifts toward continuous manufacturing, inline monitoring and process control are gaining importance. Granules from an 11 mm TSG were analysed using the Eyecon™, a real-time high speed direct imaging system, which has been used to capture accurate particle size distribution and particle count. The size parameters and particle count were then assessed in terms of their ability to be a suitable control measure using the Shewhart control charts. d10 and particle count were found to be good indicators of the change in L/S ratio. However, d50 and d90 did not reflect the change, due to their inherent variability even when the process is at steady state.
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http://dx.doi.org/10.1016/j.ijpharm.2015.09.024DOI Listing
December 2015

Elimination of the antimicrobial action of the organoarsenical cancer therapeutic, 4-(N-(S-glutathionylacetyl)amino) phenylarsonous acid, before finished product sterility testing.

J Pharm Pharmacol 2013 Nov 18;65(11):1664-9. Epub 2013 Sep 18.

Cancer Research UK Formulation Unit, Strathclyde Institute for Pharmacy and Biomedical Sciences, Robertson Wing, University of Strathclyde, Glasgow, Scotland, UK.

Objectives: Arsenical compounds have been used therapeutically for over 2000 years finding particular relevance as antimicrobials. After being replaced by more selective and consequently less toxic antibiotics in the last century, arsenicals have recently made a resurgence as anticancer drugs (specifically arsenic trioxide and its derivatives). Arsenical parenteral formulations require post-manufacture sterility testing; however, their intrinsic antimicrobial activity must be neutralised before testing to eliminate the possibility of false (no-growth) test results.

Methods: A range of thiol-containing compounds was screened to establish a suitable deactivation agent for the novel organoarsenical compound, 4-(N-(S-glutathionylacetyl)amino) phenylarsonous acid (GSAO). Dimercatopropanol (DMP) was found to successful deactivate GSAO and was validated according to pharmacopoeial sterility test guidelines (specifically the method suitability test/sterility validation test).

Key Findings: DMP is an effective way of deactivating GSAO before sterility testing and can be used for pharmacopoeial sterility tests. Our results affirm previous research highlighting the sensitivity of Staphylococcus aureus to arsenical compounds

Conclusions: A method of deactivating the arsenical drug GSAO before the post-manufacture sterility test was established and validated. DMP is a commonly used chelator/deactivation agent so this work may have implications for other inorganic therapeutic agents.
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http://dx.doi.org/10.1111/jphp.12143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7938840PMC
November 2013

Physicochemical investigation of the influence of saccharide-based parenteral formulation excipients on L-p-boronphenylalanine solubilisation for boron neutron capture therapy.

J Pharm Sci 2012 Jan 14;101(1):223-32. Epub 2011 Sep 14.

Cancer Research UK Formulation Unit, Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow G4 0RE, UK.

This paper investigates the physicochemical properties of possible pharmaceutical alternatives to L-p-boronphenylalanine (BPA)-fructose intravenous formulation currently employed in boron neutron capture therapy. The physicochemical properties of BPA in the absence and presence of fructose, mannitol, trehalose and hydroxypropyl-β-cyclodextrin (HPCD) was investigated by determination of pKa values, solubility, precipitation and dissolution using a Sirius T3 instrument. Complex formation was also assessed using (10) B-Nuclear magnetic resonance (NMR). The results indicate that fructose and mannitol form a complex with BPA through a reversible interaction with the boronic acid group, determined by changes in the pKa of the boronic acid group, the ultraviolet and NMR spectra, and increase in kinetic solubility. Trehalose and HPCD did not undergo this reaction and, consequently, did not affect boronphenylalanaine physicochemical properties. Although mannitol is complexed with BPA in an identical manner to fructose, it is superior because it provides increased kinetic solubility. Replacement of fructose by mannitol in the current clinical BPA formulation is, therefore, feasible with advantages of increased dosing and removal of issues related to fructose intolerance and calorific load. Results also indicated that important pharmaceutical parameters are the complex's solubility and dissociation behaviours rather than, as originally assumed, the complex formation reaction.
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http://dx.doi.org/10.1002/jps.22761DOI Listing
January 2012

Boron phenylalanine and related impurities: HPLC analysis, stability profile and degradation pathways.

J Pharm Biomed Anal 2011 Nov 1;56(3):633-6. Epub 2011 Jul 1.

Strathclyde Institute for Pharmacy and Biomedical Analysis, Robertson Building, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom.

Boron phenylalanine is one of the lead drug candidates in the field of Boron Neutron Capture Therapy. Its inherent low toxicity allows large doses to be administered, but this makes it important to identify, rationalise and quantify impurities. Here we report a chromatographic assay method, the conditions under which the parent compound is unstable, and the suggested degradation mechanisms.
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http://dx.doi.org/10.1016/j.jpba.2011.06.025DOI Listing
November 2011

Uptake of synthetic Low Density Lipoprotein by leukemic stem cells--a potential stem cell targeted drug delivery strategy.

J Control Release 2010 Dec 22;148(3):380-7. Epub 2010 Sep 22.

Paul O'Gorman Leukemia Research Centre, Institute of Cancer Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Gartnavel General Hospital, 1053 Great Western Road, Glasgow G120NY, United Kingdom.

Chronic Myeloid Leukemia (CML) stem/progenitor cells, which over-express Bcr-Abl, respond to imatinib by a reversible block in proliferation without significant apoptosis. As a result, patients are unlikely to be cured owing to the persistence of leukemic quiescent stem cells (QSC) capable of initiating relapse. Previously, we have reported that intracellular levels of imatinib in primary primitive CML cells (CD34+38(lo/⁻)), are significantly lower than in CML progenitor cells (total CD34+) and leukemic cell lines. The aim of this study was to determine if potentially sub-therapeutic intracellular drug concentrations in persistent leukemic QSC may be overcome by targeted drug delivery using synthetic Low Density Lipoprotein (sLDL) particles. As a first step towards this goal, however, the extent of uptake of sLDL by leukemic cell lines and CML patient stem/progenitor cells was investigated. Results with non-drug loaded particles have shown an increased and preferential uptake of sLDL by Bcr-Abl positive cell lines in comparison to Bcr-Abl negative. Furthermore, CML CD34+ and primitive CD34+38(lo/⁻) cells accumulated significantly higher levels of sLDL when compared with non-CML CD34+ cells. Thus, drug-loading the sLDL nanoparticles could potentially enhance intracellular drug concentrations in primitive CML cells and thus aid their eradication.
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http://dx.doi.org/10.1016/j.jconrel.2010.09.016DOI Listing
December 2010

Receptor dependent cellular uptake of synthetic low density lipoprotein by mammalian cells in serum-free tissue culture.

J Pharm Pharmacol 2006 Oct;58(10):1337-42

Department of Pharmaceutical Sciences, Strathclyde Institute for Biomedical Sciences, University of Strathclyde, Glasgow G4 0NR, UK.

Low density lipoprotein (LDL) is a normal plasma component, which is of interest in a number of research areas such as hypercholesterolaemia, drug targeting in cancer chemotherapy and as a lipid supplement in tissue culture systems. Currently, however, it can only be obtained by extraction from fresh plasma samples, which yields only small quantities. Synthetic LDL (sLDL) has been prepared using readily available lipid components coupled with a synthetic amphiphatic peptide molecule containing the apoprotein B receptor sequence. sLDL was capable of supporting the growth of Chinese Hamster Ovary (CHO) and fibroblast cells in serum-free culture media in a cholesterol-dependent manner that was related to the presence of the receptor peptide molecule. sLDL could be fluorescently labelled with 3,3'-dioctadecyloxalocarbocyanine perchlorate (DiO), and once labelled was assimilated by CHO and fibroblast cells in a time- and temperature-dependent manner that was dependent upon the presence of the receptor peptide. In addition, assimilation was reduced by an excess of unlabelled native LDL. The results indicated that the interaction of sLDL with CHO and fibroblast cells occurred via a receptor dependent system, most likely the LDL cellular receptor. sLDL is therefore a useful, easily obtained substitute for native LDL with potential applications in the areas of drug targeting to cells and serum-free tissue culture systems.
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http://dx.doi.org/10.1211/jpp.58.10.0006DOI Listing
October 2006

Synthetic low-density lipoprotein, a novel biomimetic lipid supplement for serum-free tissue culture.

Biotechnol Prog 2005 Jul-Aug;21(4):1262-8

Department of Pharmaceutical Sciences, Strathclyde Institute for Biomedical Sciences, University of Strathclyde, 27 Taylor Street, Glasgow G4 0NR, United Kingdom.

Lipid supplementation in serum-free tissue culture employs solubilization techniques to permit the addition of lipids, but these systems are potentially cytotoxic and do not present lipid in a natural form. In this research a simplified preparation method for synthetic low-density lipoprotein (sLDL) has been developed that involves microfluidization of a solvent lipid solution in a simple aqueous solution. This produces material with size and zeta potential characteristics similar to those of native LDL. sLDL supplementation in tissue culture media provides cholesterol concentrations higher than those achieved by 10% serum supplementation and existing chemically defined lipid supplements. sLDL stimulates NS0 and U937 cellular proliferation in completely serum-free media, the former in a lipid concentration dependent manner that is also related to both the receptor peptide structure employed and its concentration on the particle. The greatest NS0 cellular proliferation was obtained at the highest cholesterol concentration tested (0.5 mg/mL), which was 10 times higher than the cholesterol concentration achieved by standard 10% serum supplementation. U937 cellular proliferation was influenced by variation of sLDL's fatty acid constituents with a natural mixture producing maximal effect. Cell uptake studies in NS0 with fluorescently labeled sLDL indicated that assimilation is reduced by competition from native LDL. The planktonic nature of NS0 cell growth meant that cell binding and uptake experiments were difficult to conduct because of cellular aggregation. However, sLDL-induced U937 proliferation is ablated by the presence of an anti-LDL receptor antibody. The results indicate that sLDL uptake is via the LDL receptor and that sLDL can function as a lipid supplement for serum-free media capable of supplementation to cholesterol concentrations up to 0.5 mg/mL. Cellular uptake studies also suggest that sLDL will be useful for the targeting and delivery of materials to cells. sLDL therefore represents a new and promising synthetic biomimetic alternative to native LDL with multiple applications.
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http://dx.doi.org/10.1021/bp050043pDOI Listing
January 2006
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