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

A novel simulated media system for in vitro evaluation of bioequivalent intestinal drug solubility

Orally administered solid drug must dissolve in the gastrointestinal tract before absorption to provide a systemic response. Intestinal solubility is therefore crucial but difficult to measure since human intestinal fluid (HIF) is challenging to obtain, varies between fasted (Fa) and fed (Fe) states and exhibits inter and intra subject variability. A single simulated intestinal fluid (SIF) cannot reflect HIF variability, therefore current approaches are not optimal. In this study we have compared literature Fa/FeHIF drug solubilities to values measured in a novel in vitro simulated nine media system for either the fasted (Fa9SIF) or fed (Fe9SIF) state. The manuscript contains 129 literature sampled human intestinal fluid equilibrium solubility values and 387 simulated intestinal fluid equilibrium solubility values. Statistical comparison does not detect a difference (Fa/Fe9SIF vs Fa/FeHIF), a novel solubility correlation window enclosed 95% of an additional literature Fa/FeHIF data set and solubility behaviour is consistent with previous physicochemical studies. The Fa/Fe9SIF system therefore represents a novel in vitro methodology for bioequivalent intestinal solubility determination. Combined with intestinal permeability this provides an improved, population based, biopharmaceutical assessment that guides formulation development and indicates the presence of food based solubility effects. This transforms predictive ability during drug discovery and development and may represent a methodology applicable to other multicomponent fluids where no single component is responsible for performance.

Relative Bioavailability Assessment of Solid Forms by An Artificial Stomach and Duodenum Apparatus

In this work, the ability of the artificial stomach and duodenum (ASD) model to predict bioavailability in rats was investigated using a poorly soluble model compound, BI-639667. A solution and four suspensions of different solid forms of BI-639667 were tested both in an ASD and rats. Rank order of the bioavailability estimated from an ASD apparatus is consistent with that of in vivo result in rats, i.e., solution > salicylic acid cocrystal > malate salt > maleate salt > monohydrate, which correlates with the ability of the different solid forms to maintain supersaturation with respect to the stable form in aqueous solution. The results support the use of an ASD for characterizing dissolution performance of solid forms to aid their selection for tablet formulation development.

Structured solubility behaviour in fed simulated intestinal fluids

Intestinal drug solubility is a key parameter controlling absorption after the administration of a solid oral dosage form. The ability to measure fed state solubility in vitro is limited and multiple simulated intestinal fluid recipes have been developed but with no consensus which is optimal. This study has utilised nine bioequivalent simulated fed intestinal media recipes that cover over 90% of the compositional variability of sampled fed human intestinal fluid. The solubility of 24 drugs (Acidic; furosemide, ibuprofen, indomethacin, mefenamic acid, naproxen, phenytoin, piroxicam, valsartan, zafirlukast: Basic; aprepitant, atazanavir, bromocriptine, carvedilol, dipyridamole, posaconazole, tadalafil: Neutral; acyclovir, carbamazepine, felodipine, fenofibrate, griseofulvin, itraconazole, paracetamol, probucol) has been assessed to determine if structured solubility behaviour is present. The measured solubility behaviour can be split into four categories and is consistent with drug physicochemical properties and previous solubility studies. For acidic drugs (category 1) solubility is controlled by media pH and the lowest and highest pH media identify the lowest and highest solubility in 90% of cases. For weakly acidic, basic and neutral drugs (category 2) solubility is controlled by media pH and total amphiphile concentration (TAC), a consistent solubility pattern is evident with variation related to individual drug media component interactions. The lowest and highest pH × TAC media identify the lowest and highest solubility in 70% and 90% of cases respectively. Four drugs, which are non-ionised in the media systems (category 3), have been identified with a very narrow solubility range, indicating minimal impact of the simulated media on solubility. Three drugs exhibit solubility behaviour that is not consistent with the remainder (category 4). The results indicate that the use of two bioequivalent fed intestinal media from the original nine will identify in vitro the maximum and minimum solubility values for the majority of drugs and due to the media derivation this is probably applicable in vivo. When combined with a previous fasted study, this introduces interesting possibilities to measure a solubility range in vitro that can provide Quality by Design based decisions to rationalise drug and formulation development. Overall this indicates that the multi-dimensional media system is worthy of further investigation as in vitro tool to assess fed intestinal solubility.

Excipient Impact on Fenofibrate Equilibrium Solubility in Fasted and Fed Simulated Intestinal Fluids Assessed Using a Design of Experiment Protocol

Solubility is a critical parameter controlling drug absorption after oral administration. For poorly soluble drugs, solubility is influenced by the complex composition of intestinal media and the influence of dosage form excipients, which can cause bioavailability and bioequivalence issues. This study has applied a small scale design of experiment (DoE) equilibrium solubility approach in order to investigate the impact of excipients on fenofibrate solubility in simulated fasted and fed intestinal media. Seven media parameters (bile salt (BS), phospholipid (PL), fatty acid, monoglyceride, cholesterol, pH and BS/PL ratio) were assessed in the DoE and in excipient-free media, and only pH and sodium oleate in the fasted state had a significant impact on fenofibrate solubility. The impact of excipients were studied at two concentrations, and for polyvinylpyrrolidone (PVP, K12 and K29/32) and hydroxypropylmethylcellulose (HPMC, E3 and E50), two grades were studied. Mannitol had no solubility impact in any of the DoE media. PVP significantly increased solubility in a media-, grade- and concentration-dependent manner, with the biggest change in fasted media. HPMC and chitosan significantly reduced solubility in both fasted and fed states in a media-, grade- and concentration-dependent manner. The results indicate that the impact of excipients on fenofibrate solubility is a complex interplay of media composition in combination with their physicochemical properties and concentration. The results indicate that in vitro solubility studies combining the drug of interest, proposed excipients along with suitable simulated intestinal media recipes will provide interesting information with the potential to guide formulation development.

Fed Intestinal Solubility Limits and Distributions Applied to the Developability Classification System

For solid oral dosage forms drug solubility in intestinal fluid is an important parameter influencing product performance and bioavailability. Solubility along with permeability are the two parameters applied in the Biopharmaceutics and Developability Classification Systems (DCS) to assess a drug's potential for oral administration. Intestinal solubility varies with the intestinal contents and the differences between the fasted and fed states are recognised to influence solubility and bioavailability. In this study a novel fed state simulated media system comprising of nine media has been utilised to measure the solubility of seven drugs (ibuprofen, mefenamic acid, furosemide, dipyridamole, griseofulvin, paracetamol and acyclovir) previously studied in the fasted state DCS. The results demonstrate that the fed nine media system provides a range of solubility values for each drug and solubility behaviour is consistent with published design of experiment studies conducted in either the fed or fasted state. Three drugs (griseofulvin, paracetamol and acyclovir) exhibit very narrow solubility distributions, a result that matches published behaviour in the fasted state, indicating that this property is not influenced by the concentration of simulated media components. The nine solubility values for each drug can be utilised to calculate a dose/solubility volume ratio to visualise the drug's position on the DCS grid. Due to the derivation of the nine media compositions the range and catergorisation could be considered as bioequivalent and can be combined with the data from the original fed intestinal fluid analysis to provide a population based solubility distribution. This provides further information on the drugs solubility behaviour and could be applied to quality by design formulation approaches. Comparison of the fed results in this study with similar published fasted results highlight that some differences detected match in vivo behaviour in food effect studies. This indicates that a combination of the fed and fasted systems may be a useful in vitro biopharmaceutical performance tool. However, it should be noted that the fed media recipes in this study are based on a liquid meal (Ensure Plus) and this may not be representative of alternative fed states achieved through ingestion of a solid meal. Nevertheless, this novel approach provides greater in vitro detail with respect to possible in vivo biopharmaceutical performance, an improved ability to apply risk-based approaches and the potential to investigate solubility based food effects. The system is therefore worthy of further investigation but studies will be required to expand the number of drugs measured and link the in vitro measurements to in vivo results.

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

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.

Stereomicroscope with Imaging Analysis: A Versatile Tool for Wetting, Gel Formation and Erosion Rate Determinations of Eutectic Effervescent Tablet

Wettability, gel formation and erosion behaviors could influence the drug release pattern of solid dosage forms. Typically, these parameters are evaluated using a variety of techniques. Nonetheless, there has been no previous research on versatile tool development for evaluating several tablet characteristics with a single tool. The aim of this study was to develop the versatile tool for measuring various physical properties of eutectic effervescent tablets and also investigate the relationship between these parameters with parameters from drug dissolution. Ibuprofen (IBU)-poloxamer 407 (P407) eutectic effervescent tablets were fabricated with a direct compression method. Their wetting properties, gel formation and erosion behaviors were investigated using a stereomicroscope with imaging analysis in terms of the liquid penetration distance, gel thickness and erosion boundary diameter, respectively. In addition, the dissolution rate (k) and disintegration time of eutectic effervescent tablets in 0.1 N HCl buffer pH 1.2 were also determined. Incorporation of P407 into the IBU tablet improved the tablet wetting properties with increasing liquid penetration distance under stereoscope. CO₂ liberation from effervescent agents promoted tablet surface roughness from matrix erosion. The relationship between observed physical properties and disintegration and dissolution parameters suggested that the combination of erosion by effervescent agents and gel formation by P407 had a potential influence on dissolution enhancement of the formulation. Therefore, a developed stereomicroscope with an imaging analysis technique was exhibited as an alternative versatile tool for determining the wetting properties, gel formation and erosion behaviors of pharmaceutical solid dosage forms.

Understanding the Impact of Age-Related Changes in Pediatric GI Solubility by Multivariate Data Analysis

The aim of this study was to understand drug solubilization as a function of age and identify drugs at risk of altered drug solubility in newborns and young infants in comparison to adults. Multivariate statistical analysis was used to understand drug solubilization as a function of drug’s physicochemical properties and the composition of gastrointestinal fluids. The solubility of seven poorly soluble compounds was assessed in adult and age-specific fasted and fed state biorelevant media. Partial least squares regression (PLS-R) was used to assess the influence of (i) drug physicochemical properties and (ii) age-related changes in simulated GI fluids, as well as (iii) their interactions, on the pediatrics-to-adult solubility ratio (Sp/Sa (%)). For five out of seven of the compounds investigated, Sp/Sa (%) values fell outside of the 80–125% limits in at least one of the pediatric media. Lipophilicity was responsible for driving drug solubility differences between adults and children in all the biorelevant media investigated, while drug ionization was most relevant in the fed gastric media, and the fasted/fed intestinal media. The concentration of bile salts and lecithin in the fasted and fed intestinal media was critical in influencing drug solubility, while food composition (i.e., cow’s milk formula vs. soy formula) was a critical parameter in the fed gastric state. Changes in GI fluid composition between younger pediatric patients and adults can significantly alter drug luminal solubility. The use of pediatric biorelevant media can be helpful to identify the risk of altered drug solubilization in younger patients during drug development.

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

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.

Supersaturation and Solubilization upon In Vitro Digestion of Fenofibrate Type I Lipid Formulations: Effect of Droplet Size, Surfactant Concentration and Lipid Type

Lipid-based formulations (LBF) enhance oral drug absorption by promoting drug solubilization and supersaturation. The aim of the study was to determine the effect of the lipid carrier type, drop size and surfactant concentration on the rate of fenofibrate release in a bicarbonate-based in vitro digestion model. The effect of the lipid carrier was studied by preparing type I LBF with drop size ≈ 2 µm, based on medium-chain triglycerides (MCT), sunflower oil (SFO), coconut oil (CNO) and cocoa butter (CB). The drop size and surfactant concentration effects were assessed by studying MCT and SFO-based formulations with a drop size between 400 nm and 14 µm and surfactant concentrations of 1 or 10%. A filtration through a 200 nm filter followed by HPLC analysis was used to determine the aqueous fenofibrate, whereas lipid digestion was followed by gas chromatography. Shorter-chain triglycerides were key in promoting a faster drug release. The fenofibrate release from long-chain triglyceride formulations (SFO, CNO and CB) was governed by solubilization and was enhanced at a smaller droplet size and higher surfactant concentration. In contrast, supersaturation was observed after the digestion of MCT emulsions. In this case, a smaller drop size and higher surfactant had negative effects: lower peak fenofibrate concentrations and a faster onset of precipitation were observed. The study provides new mechanistic insights on drug solubilization and supersaturation after LBF digestion, and may support the development of new in silico prediction models.

Impact of gastrointestinal tract variability on oral drug absorption and pharmacokinetics: An UNGAP review

The absorption of oral drugs is frequently plagued by significant variability with potentially serious therapeutic consequences. The source of variability can be traced back to interindividual variability in physiology, differences in special populations (age- and disease-dependent), drug and formulation properties, or food-drug interactions. Clinical evidence for the impact of some of these factors on drug pharmacokinetic variability is mounting: e.g. gastric pH and emptying time, small intestinal fluid properties, differences in pediatrics and the elderly, and surgical changes in gastrointestinal anatomy. However, the link of colonic factors variability (transit time, fluid composition, microbiome), sex differences (male vs. female) and gut-related diseases (chronic constipation, anorexia and cachexia) to drug absorption variability has not been firmly established yet. At the same time, a way to decrease oral drug pharmacokinetic variability is provided by the pharmaceutical industry: clinical evidence suggests that formulation approaches employed during drug development can decrease the variability in oral exposure. This review outlines the main drivers of oral drug exposure variability and potential approaches to overcome them, while highlighting existing knowledge gaps and guiding future studies in this area.

Factors and dosage formulations affecting the solubility and bioavailability of P-glycoprotein substrate drugs

Introduction: Expression of P-glycoprotein (P-gp) increases toward the distal small intestine, implying that the duodenum is the preferential absorption site for P-gp substrate drugs. Oral bioavailability of poorly soluble P-gp substrate drugs is low and varied but increases with high-fat meals that supply lipoidal components and bile in the duodenum.Areas covered: Absorption properties of P-gp substrate drugs along with factors and oral dosage formulations affecting their solubility and bioavailability were reviewed with PubMed literature searches. An overview is provided from the viewpoint of the 'spring-and-parachute approach' that generates supersaturation of poorly soluble P-gp substrate drugs.Expert opinion: The oral bioavailability of P-gp substrate drugs is difficult to predict because of their low solubility, preferential absorption sites, and overlapping substrate specificities with CYP3A4, along with the scattered intestinal P-gp expression/function. To attain high and steady oral bioavailability of poorly soluble P-gp substrate drugs, physicochemical modification of drugs to improve solubility, or oral dosage formulations that generate long-lasting supersaturation in the duodenum, is preferred. In particular, supersaturable lipid-based drug delivery systems that can increase passive diffusion and/or lymphatic absorption are effective and applicable to many poorly soluble P-gp substrate drugs.

Eutectic mixtures as an approach to enhance solubility, dissolution rate and oral bioavailability of poorly water-soluble drugs

Eutectic mixtures have been known for a long time in the pharmaceutical field. However, its potential as a system to improve the solubility and dissolution of poorly water-soluble drugs remains little explored. Studies involving the microstructural characterization and the preparation of solid dosage forms containing eutectic mixtures are also an issue to be developed. Recently, the number of studies involving the preparation of eutectic mixtures to improve the solubility and oral bioavailability of poorly soluble drugs has increased considerably, including drug-carrier and drug-drug mixtures. In this review is discussed the potential of eutectic mixtures as an alternative pharmaceutical solid system to enhance drugs solubility, dissolution rate or oral bioavailability. Different aspects like history, physico-chemical, microstructural properties, preparation methods, mechanisms involved in solubility/dissolution enhancement, techniques for solid state characterization, in vivo studies, advantages, limitations and formulation perspective are also discussed.

Multidimensional analysis of human intestinal fluid composition

The oral administration of solid dosage forms is the commonest method to achieve systemic therapy and relies on the drug's solubility in human intestinal fluid (HIF), a key factor that influences bioavailability and biopharmaceutical classification. However, HIF is difficult to obtain and is known to be variable, which has led to the development of a range of simulated intestinal fluid (SIF) systems to determine drug solubility in vitro. In this study we have applied a novel multidimensional approach to analyse and characterise HIF composition using a published data set in both fasted and fed states with a view to refining the existing SIF approaches. The data set provided 152 and 172 measurements of five variables (total bile salt, phospholipid, total free fatty acid, cholesterol and pH) in time-dependent HIF samples from 20 volunteers in the fasted and fed state, respectively. The variable data sets for both fasted state and fed state are complex, do not follow normal distributions but the amphiphilic variable concentrations are correlated. When plotted 2-dimensionally a generally ellipsoid shaped data cloud with a positive slope is revealed with boundaries that enclose published fasted or fed HIF compositions. The data cloud also encloses the majority of fasted state and fed state SIF recipes and illustrates that the structured nature of design of experiment (DoE) approaches does not optimally cover the variable space and may examine media compositions that are not biorelevant. A principal component analysis in either fasted or fed state in combination with fitting an ellipsoid shape to enclose the data results in 8 points that capture over 95% of the compositional variability of HIF. The variable's average rate of concentration change in both fasted state and fed state over a short time scale (10 min) is zero and a Euclidean analysis highlights differences between the fasted and fed states and among individual volunteers. The results indicate that a 9-point DoE (8 + 1 central point) could be applied to investigate drug solubility in vitro and provide statistical solubility limits. In addition, a single point could provide a worst-case solubility measurement to define the lowest biopharmaceutical classification boundary or for use during drug development. This study has provided a novel description of HIF composition. The approach could be expanded in multiple ways by incorporation of further data sets to improve the statistical coverage or to cover specific patient groups (e.g., paediatric). Further development might also be possible to analyse information on the time dependent behaviour of HIF and to guide HIF sampling and analysis protocols.

Gastrointestinal diseases and their impact on drug solubility: Crohn's disease

In order to investigate differences in drug solubilisation and dissolution in luminal fluids of Crohn's disease (CD) patients and healthy subjects, biorelevant media representative of CD patients were developed using information from literature and a Design of Experiment (DoE) approach. The CD media were characterised in terms of surface tension, osmolality, dynamic viscosity and buffer capacity and compared to healthy biorelevant media. To identify which drug characteristics are likely to present a high risk of altered drug solubility in CD, the solubility of six drugs was assessed in CD media and solubility differences were related to drug properties. Identified differences in CD patients compared to healthy subjects were a reduced concentration of bile salts, a higher gastric pH and a higher colonic osmolality. Differences in the properties of CD compared to healthy biorelevant media were mainly observed for surface tension and osmolality. Drug solubility of ionisable compounds was altered in gastric CD media compared to healthy biorelevant media. For drugs with moderate to high lipophilicity, a high risk of altered drug solubilisation in CD is expected, since a significant negative effect of log P and a positive effect of bile salts on drug solubility in colonic and fasted state intestinal CD media was observed. Simulating the conditions in CD patients in vitro offers the possibility to identify relevant differences in drug solubilisation without conducting expensive clinical trials.

Gastrointestinal diseases and their impact on drug solubility: Ulcerative Colitis

For poorly soluble compounds, drug product performance in patients with Ulcerative Colitis (UC) compared to healthy subjects can be affected due to differences in drug solubility in GI fluids. A risk assessment tool was developed to identify compounds with a high risk of altered solubility in the GI fluids of UC patients. Pathophysiological changes impacting on the composition of GI fluids in UC patients were considered and UC biorelevant media representative of the stomach, intestine and colon were developed based on biorelevant media based on healthy subjects and literature data using a Design of Experiment approach. The UC media were characterised and revealed differences in surface tension, osmolality and buffer capacity compared to media based on healthy subjects. The solubility of six drugs was investigated in UC biorelevant media and results were related to media- and drug-dependent factors. A lower drug solubility in UC intestinal media was observed for compounds with a high lipophilicity. In UC simulated colonic fluids, drug solubility was altered for ionisable compounds. Additionally, a higher solubility of neutral lipophilic drugs was observed in UC fasted state colonic media with increased concentrations of soluble proteins. The developed UC biorelevant media offer the possibility to identify the risk of altered drug solubilisation in UC patients without conducting expensive clinical trials. A high risk was related to drug ionization properties and lipophilicity in the current study with all investigated drugs showing differences in solubility in biorelevant media based on UC patients compared to healthy subjects.

The Effect of Enzymes and Sodium Lauryl Sulfate on the Surface Tension of Dissolution Media: Toward Understanding the Solubility and Dissolution of Carvedilol

The objective of this work was to study the effect of the physiologically relevant enzymes pepsin, pancreatin, and the synthetic surfactant sodium lauryl sulfate (SLS) on the surface tension of the dissolution media and the solubility and dissolution of the weakly basic drug carvedilol. Compendial dissolution media and buffer solutions that simulate the gastrointestinal fluid, prepared with and without the addition of SLS, were used in this study. The surface tension of the dissolution media; critical micelle concentration (CMC) of SLS in buffer solutions; and size, polydispersity index, and zeta potential of SLS micelles loading carvedilol were determined. The solubility and dissolution of carvedilol were investigated and compared with those of the corresponding media prepared without the addition of pepsin, pancreatin, and SLS. Results showed that the addition of pepsin, pancreatin, and SLS lowered the surface tension of the dissolution media to 54.8, 55.7, and ~ 30 mN/m, respectively. The solubility of carvedilol was significantly enhanced with pepsin and SLS; however, no significant difference was found with pancreatin. The dissolution rate of carvedilol was fast in simulated gastric fluid with and without pepsin. The dissolution was further enhanced in media with pancreatin and SLS. The dissolution data were corroborated with the molar micellar solubilization (X) of SLS, ranging between 0.02 and 3.09. Understanding the effect of pepsin, pancreatin, and SLS on the surface tension of the dissolution media and the solubility and dissolution of poorly soluble drugs can improve our knowledge of the performance of these drugs in vivo.

An interlaboratory investigation of intrinsic dissolution rate determination using surface dissolution

The purpose of this study was to conduct an interlaboratory ring-study, with six partners (academic and industrial), investigating the measurement of intrinsic dissolution rate (IDR) using surface dissolution imaging (SDI) equipment. Measurement of IDR is important in pharmaceutical research as it provides characterising information on drugs and their formulations. This work allowed us to assess the SDI's interlaboratory performance for measuring IDR using a defined standard operating procedure (see supporting information) and six drugs assigned as low (tadalafil, bromocriptine mesylate), medium (carvedilol, indomethacin) and high (ibuprofen, valsartan) solubility compounds. Fasted State Simulated Intestinal Fluid (FaSSIF) and blank FaSSIF (without sodium taurocholate and lecithin) (pH 6.5) were used as media. Using the standardised protocol an IDR value was obtained for all compounds and the results show that the overall IDR rank order matched the solubility rank order. Interlaboratory variability was also examined and it was observed that the variability for lower solubility compounds was higher, coefficient of variation >50%, than for intermediate and high solubility compounds, with the exception of indomethacin in FaSSIF medium. Inter laboratory variability is a useful descriptor for understanding the robustness of the protocol and the system variability. On comparison to another published small-scale IDR study the rank ordering with respect to dissolution rate is identical except for the high solubility compounds. This results indicates that the SDI robustly measures IDR however, no recommendation on the use of one small scale method over the other is made.

Small scale design of experiment investigation of equilibrium solubility in simulated fasted and fed intestinal fluid

It is widely recognised that drug solubility within the gastrointestinal tract (GIT) differs from values determined in a simple aqueous buffer and to circumvent this problem measurement in biorelevant fluids is determined. Biorelevant fluids are complex mixtures of components (sodium taurocholate, lecithin, sodium phosphate, sodium chloride, pancreatin and sodium oleate) at various concentrations and pH levels to provide systems simulating fasted (FaSSIF) or fed (FeSSIF) intestinal media. Design of Experiment (DoE) studies have been applied to investigate FaSSIF and FeSSIF and indicate that a drug's equilibrium solubility varies over orders of magnitude, is influenced by the drug type and individual or combinations of media components, with some of these interactions being drug specific. Although providing great detail on the drug media interactions these studies are resource intensive requiring up to ninety individual experiments for FeSSIF. In this paper a low sample number or reduced DoE system has been investigated by restricting components with minimal solubility impact to a single value and only investigating variations in the concentrations of sodium taurocholate, lecithin, sodium oleate, pH and additionally in the case of fed media, monoglyceride. This reduces the experiments required to ten (FaSSIF) and nine (FeSSIF). Twelve poorly soluble drugs (Ibuprofen, Valsartan, Zafirlukast, Indomethacin, Fenofibrate, Felodipine, Probucol, Tadalafil, Carvedilol, Aprepitant, Bromocriptine and Itraconazole) were investigated and the results compared to published DoE studies and literature solubility values in human intestinal fluid (HIF), FaSSIF or FeSSIF. The solubility range determined by the reduced DoE is statistically equivalent to the larger scale published DoE results in over eighty five percent of the cases. The reduced DoE range also covers HIF, FaSSIF or FeSSIF literature solubility values. In addition the reduced DoE provides lowest measured solubility values that agree with the published DoE values in ninety percent of the cases. However, the reduced DoE only identified single and in some cases none of the major components influencing solubility in contrast to the larger published DoE studies which identified multiple individual components and component interactions. The identification of significant components within the reduced DoE was also dependent upon the drug and system under investigation. The study demonstrates that the lower experimental number reduces statistical power of the DoE to resolve the impact of media components on solubility. However, in a situation where only the solubility range is required the reduced DoE can provide the desired information, which will be of benefit during in vitro development studies. Further refinements are possible to extend the reduced DoE protocol to improve biorelevance and application into areas such as PBPK modelling.

Physiological parameters of the gastrointestinal fluid impact the dissolution behavior of the BCS class IIa drug valsartan

The objective of this study was to investigate the effect of the physiological parameters (pH, buffer capacity, and ionic strength) of the gastrointestinal (GI) fluid on the dissolution behavior of the class II weakly acidic (BCS class IIa) drug valsartan. A series of in vitro dissolution studies was carried out on Diovan^® immediate release tablets using media that cover the physiological range of pH (1.2-7.8), buffer capacity (0-0.047 M/ΔpH), and ionic strength (0-0.4 mol/L) of the GI fluid during fasted and fed states using the conventional USP II apparatus. Valsartan exhibited pH- and buffer capacity-dependent dissolution behavior, where valsartan release was slow and incomplete in media simulating gastric fluid with low pH, and fast and complete in media simulating intestinal fluid with high pH. In addition, the rate of valsartan release increased with increasing the buffer capacity of the dissolution medium. In water and NaCl solutions, valsartan release was incomplete and the dissolution profiles were similar regardless of the ionic strength of the medium, indicating an ionic strength-independent dissolution behavior. These results highlight the significant effect of the physiological parameters of the GI fluid on the dissolution behavior of BCS class IIa drugs.

In vivo models and decision trees for formulation development in early drug development: A review of current practices and recommendations for biopharmaceutical development

The ability to predict new chemical entity performance using in vivo animal models has been under investigation for more than two decades. Pharmaceutical companies use their own strategies to make decisions on the most appropriate formulation starting early in development. In this paper the biopharmaceutical decision trees available in four EFPIA partners (Bayer, Boehringer Ingelheim, Bristol Meyers Squibb and Janssen) were discussed by 7 companies of which 4 had no decision tree currently defined. The strengths, weaknesses and opportunities for improvement are discussed for each decision tree. Both pharmacokineticists and preformulation scientists at the drug discovery & development interface responsible for lead optimization and candidate selection contributed to an overall picture of how formulation decisions are progressed. A small data set containing compound information from the database designed for the IMI funded OrBiTo project is examined for interrelationships between measured physicochemical, dissolution and relative bioavailability parameters. In vivo behavior of the drug substance and its formulation in First in human (FIH) studies cannot always be well predicted from in vitro and/or in silico tools alone at the time of selection of a new chemical entity (NCE). Early identification of the risks, challenges and strategies to prepare for formulations that provide sufficient preclinical exposure in animal toxicology studies and in FIH clinical trials is needed and represents an essential part of the IMI funded OrBiTo project. This article offers a perspective on the use of in vivo models and biopharmaceutical decision trees in the development of new oral drug products.

Topography of Simulated Intestinal Equilibrium Solubility

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.

Effect of Surfactant-Bile Interactions on the Solubility of Hydrophobic Drugs in Biorelevant Dissolution Media

Biorelevant dissolution media (BDM) methods are commonly employed to investigate the oral absorption of poorly water-soluble drugs. Despite the significant progress in this area, the effect of commonly employed pharmaceutical excipients, such as surfactants, on the solubility of drugs in BDM has not been characterized in detail. The aim of this study is to clarify the impact of surfactant-bile interactions on drug solubility by using a set of 12 surfactants, 3 model hydrophobic drugs (fenofibrate, danazol, and progesterone) and two types of BDM (porcine bile extract and sodium taurodeoxycholate). Drug precipitation and sharp nonlinear decrease in the solubility of all studied drugs is observed when drug-loaded ionic surfactant micelles are introduced in solutions of both BDM, whereas the drugs remain solubilized in the mixtures of nonionic polysorbate surfactants + BDM. One-dimensional and diffusion-ordered ¹H NMR spectroscopy show that mixed bile salt + surfactant micelles with low drug solubilization capacity are formed for the ionic surfactants. On the other hand, separate surfactant-rich and bile salt-rich micelles coexist in the nonionic polysorbate surfactant + bile salt mixtures, explaining the better drug solubility in these systems. The nonionic alcohol ethoxylate surfactants show intermediate behavior. The large dependence of the drug solubility on surfactant-bile interactions (in which the drug molecules do not play a major role per se) highlights how the complex interplay between excipients and bile salts can significantly change one of the key parameters which governs the oral absorption of poorly water-soluble drugs, viz. the drug solubility in the intestinal fluids.

Automated assays for thermodynamic (equilibrium) solubility determination

Solubility is a crucial physicochemical property for drug candidates and is important in both drug discovery and development. Poor solubility is detrimental to absorption after oral administration and can mask compound activity in bioassays in various ways. Hence, solubility liabilities should ideally be identified as early as possible in the drug development process. With the increasing number of compounds as potential drug candidates, automated thermodynamic solubility assays for high throughput screening enabling rapid evaluation of a large number of compounds are becoming increasingly important. This review discusses the current status of the most widely used automated assays for thermodynamic solubility, followed by recent high throughput measurements of properties related to solubility (e.g. dissolution rate and supersaturation) and a brief overview of predictive computational methods for thermodynamic solubility reported in the literature.

A Miniaturized Extruder to Prototype Amorphous Solid Dispersions: Selection of Plasticizers for Hot Melt Extrusion

Hot-melt extrusion is an option to fabricate amorphous solid dispersions and to enhance oral bioavailability of poorly soluble compounds. The selection of suitable polymer carriers and processing aids determines the dissolution, homogeneity and stability performance of this solid dosage form. A miniaturized extrusion device (MinEx) was developed and Hypromellose acetate succinate type L (HPMCAS-L) based extrudates containing the model drugs neurokinin-1 (NK1) and cholesterylester transfer protein (CETP) were manufactured, plasticizers were added and their impact on dissolution and solid-state properties were assessed. Similar mixtures were manufactured with a lab-scale extruder, for face to face comparison. The properties of MinEx extrudates widely translated to those manufactured with a lab-scale extruder. Plasticizers, Polyethyleneglycol 4000 (PEG4000) and Poloxamer 188, were homogenously distributed but decreased the storage stability of the extrudates. Stearic acid was found condensed in ultrathin nanoplatelets which did not impact the storage stability of the system. Depending on their distribution and physicochemical properties, plasticizers can modulate storage stability and dissolution performance of extrudates. MinEx is a valuable prototyping-screening method and enables rational selection of plasticizers in a time and material sparing manner. In eight out of eight cases the properties of the extrudates translated to products manufactured in lab-scale extrusion trials.

Statistical investigation of the full concentration range of fasted and fed simulated intestinal fluid on the equilibrium solubility of oral drugs

Upon oral administration the solubility of a drug in intestinal fluid is a key property influencing bioavailability. It is also recognised that simple aqueous solubility does not reflect intestinal solubility and to optimise in vitro investigations simulated intestinal media systems have been developed. Simulated intestinal media which can mimic either the fasted or fed state consists of multiple components each of which either singly or in combination may influence drug solubility, a property that can be investigated by a statistical design of experiment technique. In this study a design of experiment covering the full range from the lower limit of fasted to the upper limit of fed parameters and using a small number of experiments has been performed. The measured equilibrium solubility values are comparable with literature values for simulated fasted and fed intestinal fluids as well as human fasted and fed intestinal fluids. The equilibrium solubility data range is statistically equivalent to a combination of published fasted and fed design of experiment data in six (indomethacin, phenytoin, zafirlukast, carvedilol, fenofibrate and probucol) drugs with three (aprepitant, tadalafil and felodipine) drugs not equivalent. In addition the measured equilibrium solubility data sets were not normally distributed. Further studies will be required to determine the reasons for these results however it implies that a single solubility measurement without knowledge of the solubility distribution will be of limited value. The statistically significant media factors which promote equilibrium solubility (pH, sodium oleate and bile salt) were in agreement with published results but the number of determined significant factors and factor interactions was fewer in this study, lecithin for example did not influence solubility. This may be due to the reduction in statistical sensitivity from the lower number of experimental data points or the fact that using the full range will examine media parameters ratios that are not biorelevant. Overall the approach will provide an estimate of the solubility range and the most important media factors but will not be equivalent to larger scale focussed studies. Further investigations will be required to determine why some drugs do not produce equivalent DoE solubility distributions, for example combined fasted and fed DoE, but this simply may be due to the complexity and individuality of the interactions between a drug and the media components.

Dual Level Statistical Investigation of Equilibrium Solubility in Simulated Fasted and Fed Intestinal Fluid

The oral route is the preferred option for drug administration but contains the inherent issue of drug absorption from the gastro-intestinal tract (GIT) in order to elicit systemic activity. A prerequisite for absorption is drug dissolution, which is dependent upon drug solubility in the variable milieu of GIT fluid, with poorly soluble drugs presenting a formulation and biopharmaceutical challenge. Multiple factors within GIT fluid influence solubility ranging from pH to the concentration and ratio of amphiphilic substances, such as phospholipid, bile salt, monoglyceride, and cholesterol. To aid in vitro investigation simulated intestinal fluids (SIF) covering the fasted and fed state have been developed. SIF media is complex and statistical design of experiment (DoE) investigations have revealed the range of solubility values possible within each state due to physiological variability along with the media factors and factor interactions which influence solubility. However, these studies require large numbers of experiments (>60) and are not feasible or sensible within a drug development setting. In the current study a smaller dual level, reduced experimental number (20) DoE providing three arms covering the fasted and fed states along with a combined analysis has been investigated. The results indicate that this small scale investigation is feasible and provides solubility ranges that encompass published data in human and simulated fasted and fed fluids. The measured fasted and fed solubility ranges are in agreement with published large scale DoE results in around half of the cases, with the differences due to changes in media composition between studies. Indicating that drug specific behaviors are being determined and that careful media factor and concentration level selection is required in order to determine a physiologically relevant solubility range. The study also correctly identifies the major single factor or factors which influence solubility but it is evident that lower significance factors (for example bile salt) are not picked up due to the lower sample number employed. A similar issue is present with factor interactions with only a limited number available for study and generally not determined to have a significant solubility impact due to the lower statistical power of the study. The study indicates that a reduced experimental number DoE is feasible, will provide solubility range results with identification of major solubility factors however statistical limitations restrict the analysis. The approach therefore represents a useful initial screening tool that can guide further in depth analysis of a drug's behavior in gastrointestinal fluids.

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

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.