Precipitation in the small intestine may play a more important role in the in vivo performance of poorly soluble weak bases in the fasted state: Case example nelfinavir

In vivo deposition of poorly soluble drugs

Administered drug molecules, whether dissolved or solubilized, have the potential to precipitate and accumulate as solid forms in tissues and cells within the body. This phase transition can significantly impact the pharmacokinetics of treatment. It is thus crucial to gain an understanding of how drug solubility/permeability, drug formulations and routes of administration affect in vivo behaviors of drug deposition. This review examines literature reports on the drug deposition in tissues and cells of poorly water-soluble drugs, as well as underlying physical mechanisms that lead to precipitation. Our work particularly highlights drug deposition in macrophages and the subcellular fate of precipitated drugs. We also propose a tissue permeability-based classification framework to evaluate precipitation potentials of poorly soluble drugs in major organs and tissues. The impact on pharmacokinetics is further discussed and needs to be considered in developing drug delivery systems. Finally, bioimaging techniques that are used to examine aggregated states and the intracellular trafficking of absorbed drugs are summarized.

Importance of Considering Fed-State Gastrointestinal Physiology in Predicting the Reabsorption of Enterohepatic Circulation of Drugs

PURPOSE

The purpose of this study was to develop a simulation model for the pharmacokinetics (PK) of drugs undergoing enterohepatic circulation (EHC) with consideration to the environment in the gastrointestinal tract in the fed state in humans. The investigation particularly focused on the necessity of compensating for the permeability rate constant in the reabsorption process in consideration of drug entrapment in bile micelles.

METHODS

Meloxicam and ezetimibe were used as model drugs. The extent of the entrapment of drugs inside bile micelles was evaluated using the solubility ratio of Fed State Simulated Intestinal Fluid version 2 (FeSSIF-V2) to Fasted State Simulated Intestinal Fluid version 2 (FaSSIF-V2). Prediction accuracy was evaluated using the Mean Absolute Percentage Error (MAPE) value, calculated from the observed and predicted oral PK profiles.

RESULTS

The solubilization of ezetimibe by bile micelles was clearly observed while that of meloxicam was not. Assuming that only drugs in the free fraction of micelles permeate through the intestinal membrane, PK simulation for ezetimibe was performed in both scenarios with and without compensation by the permeation rate constant. The MAPE value of Zetia® tablet, containing ezetimibe, was lower with compensation than without compensation. By contrast, Mobic® tablet, containing meloxicam, showed a relatively low MAPE value even without compensation.

CONCLUSION

For drugs which undergo EHC and can be solubilized by bile micelles, compensating for the permeation rate constant in the reabsorption process based on the free fraction ratio appears an important factor in increasing the accuracy of PK profile prediction.

An In Vitro Model for Cocrystal Dissolution with Simultaneous Surface and Bulk Precipitation

Cocrystals can be promising means of overcoming the poor aqueous solubility of many drugs. However, precipitation of the stable drug at the cocrystal surface or in the bulk medium is often provoked during cocrystal dissolution due to high drug supersaturation, which prevents sustaining high drug concentrations for enhanced bioavailability. There is a need for predictive in vitro models that can accurately describe this cocrystal dissolution-supersaturation-precipitation (DSP) process to aid drug development and formulation design. Consideration of surface precipitation is often essential for such models given the strong impact of surface precipitation on the drug concentration during cocrystal dissolution. However, DSP models that can explicitly account for the effect of surface precipitation are currently lacking. This work presents a population balance-based model to describe in vitro cocrystal DSP behavior, which accounts for cocrystal dissolution, surface precipitation, and bulk precipitation. Dissolution experiments with carbamazepine-succinic acid cocrystals are conducted for model development and validation. The developed model captures all of the principal experimental trends and predicts the dose-dependent DSP behavior outside the regression data set with reasonable accuracy. The results show that surface precipitation is an essential component of the model. Finally, the new model is integrated with numerical optimization to illustrate how it can be used to identify an optimal dose, particle size, and amount of predissolved coformer.

The biomolecular gastrointestinal corona in oral drug delivery

The formation of a biomolecular corona on exogenous particles in plasma is well studied and is known to dictate the biodistribution and cellular interactions of nanomedicine formulations. In contrast, while the oral route is the most favorable administration method for pharmaceuticals, little is known about the formation and composition of the corona formed by biomolecules on particles within the gastrointestinal tract. This work reviews the current literature understanding of (1) the formation of drug particles after oral administration, (2) the formation of a biomolecular corona within the gastrointestinal tract ("the gastrointestinal corona"), and (3) the possible implications of the formation of a gastrointestinal corona on the interactions of drug particles with their biological environment. In doing so, this work aims to establish the significance of the formation of a gastrointestinal corona in oral drug delivery to ultimately arrive at new avenues to control the behavior of orally administered pharmaceuticals.

Application of an AI image analysis and classification approach to characterise dissolution and precipitation events in the flow through apparatus

Imaging and artificial intelligence (AI) approaches have been used with increasing frequency in pharmaceutical industry in recent years. Characterisation of processes such as drug dissolution and precipitation is vital in quality control testing and drug manufacture. To support existing techniques like in vitro dissolution testing, novel process analytical technologies (PATs) can give an insight into these processes. The aim of this study was to create and explore the potential of an automated image classification model based on image analysis to identify events (dissolution and precipitation) occurring in the flow-through apparatus (FTA) test cell, and the ability to characterise a dissolution process over time. Several precipitation conditions were tested in a USP 4 FTA test cell with images recorded during early (plume formation) and late (particulate re-formation) stages of precipitation. An available MATLAB code was used as a base to develop and validate an anomaly classification model able to detect different events occurring during the precipitation process in the dissolution cell. Two variants of the model were tested on images from a dissolution test in the FTA, with a view to application of the image analysis system to quantitative characterization of the dissolution process over time. It was found that the classification model is highly accurate (>90%) in detecting events occurring in the FTA test cell. The model showed potential to be used to characterise the stages of dissolution and precipitation processes, and as a proof of concept demonstrates potential for deep machine learning image analysis to be applied to kinetics of other pharmaceutical processes.

Dissolution of a Biopharmaceutics Classification System Class II Free Acid from Immediate Release Tablets Containing a Microenvironmental pH Modulator: Comparison of a Biorelevant Bicarbonate Buffering System with Phosphate Buffers

Poor water dissolution of active pharmaceutical ingredients (API) limits the rate of absorption from the gastrointestinal tract. Increasing the pH of a solid form microenvironment can enhance the dissolution of weakly acidic drugs, but data on this phenomenon in a physiologically relevant bicarbonate media are lacking. In this paper, we examined the effect of a microenvironmental pH modulator (Na₂HPO₄) on the dissolution of a Biopharmaceutics Classification System (BCS) class II free weak acid (ibuprofen) at biorelevant conditions, including an automatic bicarbonate buffering system, as well as in compendial (50 mM) and low-concentration (10 mM) phosphate buffers with no external pH control. The tablets of 200 mg ibuprofen with either Na₂HPO₄ (phosphate formulation, PF) or NaCl (reference formulation, RF) were manufactured using a compression method. In a pH 2 simulated gastric fluid, only PF produced a transient supersaturation of ibuprofen, dissolving a fourfold higher drug amount than RF. In a bicarbonate-buffered simulated intestinal fluid with a dynamically controlled pH (5.7, 7.2, and 5.8 to 7.7 gradient), PF dissolved more drug within 30 min than RF (p ≤ 0.019). Of note, the use of a 50 mM phosphate buffer pH 7.2 provided opposite results-RF dissolved the API much faster than PF. Moreover, 10 mM phosphate buffers of pH 5.6 and 7.2 could neither maintain a constant pH nor mimic the bicarbonate buffer performance. In conclusion, the use of a bicarbonate-buffered intestinal fluid, instead of phosphate buffers, may be essential in dissolution tests of BCS class II drugs combined with pH modulators.

Importance of Gastric Secretion and the Rapid Gastric Emptying of Ingested Water along the Lesser Curvature ("Magenstraße") in Predicting the In Vivo Performance of Liquid Oral Dosage Forms in the Fed State Using a Modeling and Simulation

The objective of the present study was to develop an in silico model of the stomach for predicting oral drug absorption in fed humans. We focused on a model capable of simulating dynamic fluid volume changes and included a simulated Magenstraße "stomach road," a route along the lesser curvature that often carries fluids rapidly to assess the gastric emptying of drugs. Two types of model liquid drug formulations, liquid-filled soft gelatin capsules (enzalutamide, cyclosporine, and nifedipine) and oral solutions (levofloxacin and fenfluramine), were used. An in silico model was assembled, and simulations were performed using Stella Professional software. The secretion rate of the gastric juice induced by food ingestion was assessed along with the gastric emptying of the ingested water via the Magenstraße in the fed state. The model for the fed state successfully described the in vivo performance of the model drug formulations. These results clearly indicate the importance of including gastric secretion and the kinetics of Magenstraße when predicting the in vivo performance of dosage forms using an in silico modeling and simulation of fed humans. This simulation model should be further optimized to allow for the different physiological mechanisms following the ingestion of different types of meals, as well as modifications for interindividual and intraindividual variabilities in gastrointestinal physiology in the fed state in the future.

pH-Dependent supersaturation from amorphous solid dispersions of weakly basic drugs

PURPOSE

In amorphous solid dispersions (ASDs), the chemical potential of a drug can be reduced due to mixing with the polymer in the solid matrix, and this can lead to reduced drug release when the polymer is insoluble in the dissolution media. If both the drug and the polymer composing an ASD are ionizable, drug release from the ASD becomes pH-dependent. The goal of this study was to gain insights into the pH-dependent solubility suppression from ASD formulations.

METHODS

The maximum release of clotrimazole, a weakly basic drug, from ASDs formulated with insoluble and pH-responsive polymers, was determined as a function of solution pH. Drug-polymer interactions in ASDs were probed using melting point depression, moisture sorption, and solid-state Nuclear Magnetic Resonance spectroscopy (SSNMR) measurements.

RESULTS

The extent of solubility suppression was dependent on polymer type and drug loading. The strength of drug-polymer interactions was found to correlate well with the degree of solubility suppression. For the same ASD, the degree of solubility suppression was nearly constant across the solution pH range studied, suggesting that polymer-drug interactions in residual ASD solids was independent of solution pH. The total drug release agrees with the Henderson-Hasselbalch relationship if the suppressed amorphous solubility of the free drug is independent of solution pH.

CONCLUSIONS

The mechanism of solubility suppression at different solution pHs appeared to be drug-polymer interactions in the solid-state, where the concentration of the free drug remains the same at variable pHs and the total drug concentration follows the Henderson-Hasselbalch relationship.

Prediction of in vivo supersaturation and precipitation of poorly water-soluble drugs: Achievements and aspirations

This review focuses on options available to a pharmaceutical scientist to predict in vivo supersaturation and precipitation of poorly water-soluble drugs. As no single device or system can simulate the complex gastrointestinal environment, a combination of appropriate in vitro tools may be utilized to get optimal predictive information. To address the empirical issues encountered during small-scale and full-scale in vitro predictive testing, theoretical background and relevant case studies are discussed. The practical considerations for selection of appropriate tools at various stages of drug development are recommended. Upcoming technologies that have potential to further reduce in vivo studies and expedite the drug development process are also discussed.

Use of Physiologically Based Pharmacokinetic (PBPK) Modeling for Predicting Drug-Food Interactions: an Industry Perspective

The effect of food on pharmacokinetic properties of drugs is a commonly observed occurrence affecting about 40% of orally administered drugs. Within the pharmaceutical industry, significant resources are invested to predict and characterize a clinically relevant food effect. Here, the predictive performance of physiologically based pharmacokinetic (PBPK) food effect models was assessed via de novo mechanistic absorption models for 30 compounds using controlled, pre-defined in vitro, and modeling methodology. Compounds for which absorption was known to be limited by intestinal transporters were excluded in this analysis. A decision tree for model verification and optimization was followed, leading to high, moderate, or low food effect prediction confidence. High (within 0.8- to 1.25-fold) to moderate confidence (within 0.5- to 2-fold) was achieved for most of the compounds (15 and 8, respectively). While for 7 compounds, prediction confidence was found to be low (> 2-fold). There was no clear difference in prediction success for positive or negative food effects and no clear relationship to the BCS category of tested drug molecules. However, an association could be demonstrated when the food effect was mainly related to changes in the gastrointestinal luminal fluids or physiology, including fluid volume, motility, pH, micellar entrapment, and bile salts. Considering these findings, it is recommended that appropriately verified mechanistic PBPK modeling can be leveraged with high to moderate confidence as a key approach to predicting potential food effect, especially related to mechanisms highlighted here.

The Introduction of a New Flexible In Vivo Predictive Dissolution Apparatus, GIS-Alpha (GIS-α), to Study Dissolution Profiles of BCS Class IIb Drugs, Dipyridamole and Ketoconazole

The physiological pH changes and peristalsis activities in gastrointestinal (GI) tract have big impact on the dissolution of oral drug products, when those oral drug products include APIs with pH-dependent solubility. It is well documented that predicting the bioperformance of those oral drug products can be challenging using compendial methods. To overcome this limitation, in vivo predictive dissolution apparatuses, such as the transfer model, have been developed to predict bioperformance of oral formulation candidates and drug products. In this manuscript we utilize a new transfer-model dissolution apparatus, the gastrointestinal simulator-α (GIS-α), to characterize its behavior in terms of transfer kinetics and pH, assess its reproducibility and adaptability to mimic different transfer conditions, as well as study dissolution of ketoconazole and dipyridamole as model BCS class IIb compounds. Availability of commercially available dissolution transfer systems with similar configuration to compendial dissolution apparatus, may be helpful to simplify and standardize in vivo predictive dissolution methodologies for BCS class IIb compounds in the future.

Food Effects on Oral Drug Absorption: Application of Physiologically-Based Pharmacokinetic Modeling as a Predictive Tool

The bioavailability of an orally administered small molecule is often dictated by drug-specific physicochemical characteristics and is influenced by many biological processes. For example, in fed or fasted conditions, the transit time within the gastrointestinal tract can vary, confounding the ability to predict the oral absorption. As such, the effects of food on the pharmacokinetics of compounds in the various biopharmaceutics classification system (BCS) classes need to be assessed. The consumption of food leads to physiological changes, including fluctuations in the gastric and intestinal pH, a delay in gastric emptying, an increased bile secretion, and an increased splanchnic and hepatic blood flow. Despite the significant impact of a drug's absorption and dissolution, food effects have not been fully studied and are often overlooked. Physiologically-based pharmacokinetic (PBPK) models can be used to mechanistically simulate a compound's pharmacokinetics under fed or fasted conditions, while integrating drug properties such as solubility and permeability. This review discusses the PBPK models published in the literature predicting the food effects, the models' strengths and shortcomings, as well as future steps to mitigate the current knowledge gap. We observed gaps in knowledge which limits the ability of PBPK models to predict the negative food effects and food effects in the pediatric population. Overall, the further development of PBPK models to predict food effects will provide a mechanistic basis to understand a drug's behavior in fed and fasted conditions, and will help enable the drug development process.

Amorphous solid dispersions of weak bases with pH-dependent soluble polymers to overcome limited bioavailability due to gastric pH variability - An in-vitro approach

Several drugs are pH-dependent soluble weak bases with a poor solubility in the intestinal pH range. Additionally a variable gastric pH, which is a common issue in the population, potentially reduces the in-vivo performance due to reduced solubility at elevated pH. Aiming to avoid the influence of variable gastric pH on the dissolution performance, enteric polymers - hydroxypropylmethylcellulose acetate succinate (HPMCAS), hydroxypropylmethylcellulose phthalate (HP-55, HP-50) and methacrylic acid ethylacrylate copolymer (Eudragit L100-55) together with nevirapine as model drug were used for the preparation of solid dispersions by hot-melt extrusion. We were able to generate solid dispersions without crystalline residuals. The resulting solid dispersions were further tested for stability and dissolution performance applying two different pH-shift experiments (non-sink conditions), to simulate standard and altered gastric conditions. Solid dispersions made of enteric polymers were independent to gastric pH variability and exhibited superior dissolution performances compared to their respective physical mixtures and neat nevirapine.

Enhancing oral bioavailability of poorly soluble drugs with mesoporous silica based systems: opportunities and challenges

Porous silica-based drug delivery systems have shown considerable promise for improving the oral delivery of poorly water-soluble drugs. More specifically, micro- and meso-porous silica carriers have high surface areas with associated ability to physically adsorb high-drug loads in a molecular or amorphous form; this allows molecular state drug release in aqueous gastrointestinal environments, potential for supersaturation, and hence facilitates enhanced absorption and increased bioavailability. This review focuses primarily on the ability of porous silica materials to modulate in vitro drug release and enhance in vivo biopharmaceutical performance. The key considerations identified and addressed are the physicochemical properties of the porous silica materials (e.g. the particle and pore size, shape, and surface chemistry), drug specific properties (e.g. pKa, solubility, and nature of interactions with the silica carrier), potential for both immediate and controlled release, drug release mechanisms, potential for surface functionalization and inclusion of precipitation inhibitors, and importance of utilizing relevant and effective in vitro dissolution methods with discriminating dissolution media that provides guidance for in vivo outcomes (i.e. IVIVC).

Lipid Architectonics for Superior Oral Bioavailability of Nelfinavir Mesylate: Comparative in vitro and in vivo Assessment

Nelfinavir mesylate (NFV), a human immunodeficiency virus (HIV) protease inhibitor, is an integral component of highly active anti retro viral therapy (HAART) for management of AIDS. NFV possesses pH-dependent solubility and has low and variable bioavailability hampering its use in therapeutics. Lipid-based particulates have shown to improve solubility of poorly water soluble drugs and oral absorption, thereby aiding in improved bioavailability. The current study compares potential of vesicular and solid lipid nanocarriers of NFV with drug nanocrystallites and microvesicular systems like cochleates in improving bioavailability of NFV. The paper outlines investigation of systems using in vitro models like in vitro lipolysis, in vitro release, and permeation through cell lines to predict the in vivo potential of nanocarriers. Finally, in vivo pharmacokinetic study is reported which provided proof of concept in sync with results from in vitro studies. Graphical Abstract ᅟ.

In Vitro, in Silico, and in Vivo Assessments of Intestinal Precipitation and Its Impact on Bioavailability of a BCS Class 2 Basic Compound

In this study, a multipronged approach of in vitro experiments, in silico simulations, and in vivo studies was developed to evaluate the dissolution, supersaturation, precipitation, and absorption of three formulations of Compound-A, a BCS class 2 weak base with pH-dependent solubility. In in vitro 2-stage dissolution experiments, the solutions were highly supersaturated with no precipitation at the low dose but increasing precipitation at higher doses. No difference in precipitation was observed between the capsules and tablets. The in vitro precipitate was found to be noncrystalline with higher solubility than the crystalline API, and was readily soluble when the drug concentration was lowered by dilution. A gastric transit and biphasic dissolution (GTBD) model was developed to better mimic gastric transfer and intestinal absorption. Precipitation was also observed in GTBD, but the precipitate redissolved and partitioned into the organic phase. In vivo data from the phase 1 clinical trial showed linear and dose proportional PK for the formulations with no evidence of in vivo precipitation. While the in vitro precipitation observed in the 2-stage dissolution appeared to overestimate in vivo precipitation, the GTBD model provided absorption profiles consistent with in vivo data. In silico simulation of plasma concentrations by GastroPlus using biorelevant in vitro dissolution data from the tablets and capsules and assuming negligible precipitation was in line with the observed in vivo profiles of the two formulations. The totality of data generated with Compound-A indicated that the bioavailability differences among the three formulations were better explained by the differences in gastric dissolution than intestinal precipitation. The lack of intestinal precipitation was consistent with several other BCS class 2 basic compounds in the literature for which highly supersaturated concentrations and rapid absorption were also observed.

Predictive Performance of Physiologically Based Pharmacokinetic Models for the Effect of Food on Oral Drug Absorption: Current Status

A comprehensive search in literature and published US Food and Drug Administration reviews was conducted to assess whether physiologically based pharmacokinetic (PBPK) modeling could be prospectively used to predict clinical food effect on oral drug absorption. Among the 48 resulted food effect predictions, ∼50% were predicted within 1.25‐fold of observed, and 75% within 2‐fold. Dissolution rate and precipitation time were commonly optimized parameters when PBPK modeling was not able to capture the food effect. The current work presents a knowledgebase for documenting PBPK experience to predict food effect.

The impact of supersaturation level for oral absorption of BCS class IIb drugs, dipyridamole and ketoconazole, using in vivo predictive dissolution system: Gastrointestinal Simulator (GIS)

The development of formulations and the assessment of oral drug absorption for Biopharmaceutical Classification System (BCS) class IIb drugs is often a difficult issue due to the potential for supersaturation and precipitation in the gastrointestinal (GI) tract. The physiological environment in the GI tract largely influences in vivo drug dissolution rates of those drugs. Thus, those physiological factors should be incorporated into the in vitro system to better assess in vivo performance of BCS class IIb drugs. In order to predict oral bioperformance, an in vitro dissolution system with multiple compartments incorporating physiologically relevant factors would be expected to more accurately predict in vivo phenomena than a one-compartment dissolution system like USP Apparatus 2 because, for example, the pH change occurring in the human GI tract can be better replicated in a multi-compartmental platform. The Gastrointestinal Simulator (GIS) consists of three compartments, the gastric, duodenal and jejunal chambers, and is a practical in vitro dissolution apparatus to predict in vivo dissolution for oral dosage forms. This system can demonstrate supersaturation and precipitation and, therefore, has the potential to predict in vivo bioperformance of oral dosage forms where this phenomenon may occur. In this report, in vitro studies were performed with dipyridamole and ketoconazole to evaluate the precipitation rates and the relationship between the supersaturation levels and oral absorption of BCS class II weak base drugs. To evaluate the impact of observed supersaturation levels on oral absorption, a study utilizing the GIS in combination with mouse intestinal infusion was conducted. Supersaturation levels observed in the GIS enhanced dipyridamole and ketoconazole absorption in mouse, and a good correlation between their supersaturation levels and their concentration in plasma was observed. The GIS, therefore, appears to represent in vivo dissolution phenomena and demonstrate supersaturation and precipitation of dipyridamole and ketoconazole. We therefore conclude that the GIS has been shown to be a good biopredictive tool to predict in vivo bioperformance of BCS class IIb drugs that can be used to optimize oral formulations.

The in vivo fate of nanocrystals

There has been significant research interest in, and development of, nanocrystals in recent years for the delivery of poorly water-soluble drugs via various routes. However, there is a common misinterpretation of nanocrystallization as an approach to modulate, and more specifically to enhance, the dissolution of drug crystals. Nevertheless, it is possible for nanocrystals to interact with biological tissues because nanocrystals can survive for a longer duration in vivo compared with solution counterparts. Therefore, understanding the in vivo fate of nanocrystals and determining its contribution to efficacy is of tremendous significance for optimizing the performance of nanocrystals. Here, we critically review the general hypotheses related to the in vivo fate of nanocrystals.

Compositional effect of complex biorelevant media on the crystallization kinetics of an active pharmaceutical ingredient

Bile salts impact crystal nucleation and growth of supersaturated solutions of poorly water soluble drugs.

A solid self-nanoemulsifying system of the BCS class IIb drug dabigatran etexilate to improve oral bioavailability

Aim: To develop dabigatran etexilate (DE)-loaded self-nanoemulsifying drug delivery systems (SNEDDS) for the prevention of stroke and thromboembolism. Materials & methods: SNEDDS were optimized by ternary phase diagrams and then further solidified into dispersible tablets. In vitro dissolution was analyzed by a phase distribution study. In situ absorption and in vivo pharmacokinetic studies were tested in male Sprague-Dawley rats. Results: The phase distribution study showed that more than 60% of DE was retained in the oil phase. Dissolution rate was dramatically enhanced without significant precipitation (<30%) in simulated intestinal fluid. Optimized SNEDDS had 531.80% relative bioavailability compared with Pradaxa® capsules (a commercial DE product). Conclusion: The developed SNEDDS are promising materials for improving the dissolution and oral bioavailability of BCS class IIb drugs.

Co-Amorphous Combination of Nateglinide-Metformin Hydrochloride for Dissolution Enhancement

The aim of the present work was to prepare a co-amorphous mixture (COAM) of Nateglinide and Metformin hydrochloride to enhance the dissolution rate of poorly soluble Nateglinide. Nateglinide (120 mg) and Metformin hydrochloride (500 mg) COAM, as a dose ratio, were prepared by ball-milling technique. COAMs were characterized for saturation solubility, amorphism and physicochemical interactions (X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR)), SEM, in vitro dissolution, and stability studies. Solubility studies revealed a sevenfold rise in solubility of Nateglinide from 0.061 to 0.423 mg/ml in dose ratio of COAM. Solid-state characterization of COAM suggested amorphization of Nateglinide after 6 h of ball milling. XRPD and DSC studies confirmed amorphism in Nateglinide, whereas FTIR elucidated hydrogen interactions (proton exchange between Nateglinide and Metformin hydrochloride). Interestingly, due to low energy of fusion, Nateglinide was completely amorphized and stabilized by Metformin hydrochloride. Consequently, in vitro drug release showed significant increase in dissolution of Nateglinide in COAM, irrespective of dissolution medium. However, little change was observed in the solubility and dissolution profile of Metformin hydrochloride, revealing small change in its crystallinity. Stability data indicated no traces of devitrification in XRPD of stability sample of COAM, and % drug release remained unaffected at accelerated storage conditions. Amorphism of Nateglinide, proton exchange with Metformin hydrochloride, and stabilization of its amorphous form have been noted in ball-milled COAM of Nateglinide-Metformin hydrochloride, revealing enhanced dissolution of Nateglinide. Thus, COAM of Nateglinide-Metformin hydrochloride system is a promising approach for combination therapy in diabetic patients.

pH-Dependent Solubility and Dissolution Behavior of Carvedilol--Case Example of a Weakly Basic BCS Class II Drug

The objective of this study was to investigate the pH-dependent solubility and dissolution of weakly basic Biopharmaceutical Classification Systems (BCS) class II drugs, characterized by low solubility and high permeability, using carvedilol, a weak base with a pK a value of 7.8, as a model drug. A series of solubility and in vitro dissolution studies was carried out using media that simulate the gastric and intestinal fluids and cover the physiological pH range of the GI from 1.2 to 7.8. The effect of ionic strength, buffer capacity, and buffer species of the dissolution media on the solubility and dissolution behavior of carvedilol was also investigated. The study revealed that carvedilol exhibited a typical weak base pH-dependent solubility profile with a high solubility at low pH (545.1-2591.4 μg/mL within the pH range 1.2-5.0) and low solubility at high pH (5.8-51.9 μg/mL within the pH range 6.5-7.8). The dissolution behavior of carvedilol was consistent with the solubility results, where carvedilol release was complete (95.8-98.2% released within 60 min) in media simulating the gastric fluid (pH 1.2-5.0) and relatively low (15.9-86.2% released within 240 min) in media simulating the intestinal fluid (pH 6.5-7.8). It was found that the buffer species of the dissolution media may influence the solubility and consequently the percentage of carvedilol released by forming carvedilol salts of varying solubilities. Carvedilol solubility and dissolution decreased with increasing ionic strength, while lowering the buffer capacity resulted in a decrease in carvedilol solubility and dissolution rate.

Supersaturation and Precipitation of Posaconazole Upon Entry in the Upper Small Intestine in Humans

The purpose of this study was to explore gastrointestinal dissolution, supersaturation and precipitation of the weakly basic drug posaconazole in humans, and to assess the impact of formulation pH and type on these processes. In a cross-over study, two posaconazole suspensions (40 mg dispersed in 240 mL water at pH 1.6 and pH 7.1, respectively) were intragastrically administered; subsequently, gastric and duodenal fluids were aspirated. In parallel, blood samples were collected. Additionally, posaconazole was intragastrically administered as a solution (20 mg in 240 mL water, pH 1.6). When posaconazole was administered as an acidified suspension, supersaturated duodenal concentrations of posaconazole were observed for approximately 45 min. However, extensive intestinal precipitation was observed. Administration of the neutral suspension resulted in subsaturated concentrations with a mean duodenal AUC0-120 min and Cmax being approximately twofold lower than for the acidified suspension. The mean plasma AUC0-8 h of posaconazole was also twofold higher following administration of the acidified suspension. Similar to the acidified suspension, significant intestinal precipitation (up to 92%) was observed following intragastric administration of the posaconazole solution. This study demonstrated for the first time the gastrointestinal behavior of a weakly basic drug administered in different conditions, and its impact on systemic exposure.

Quality-by-design based development of a self-microemulsifying drug delivery system to reduce the effect of food on Nelfinavir mesylate

Poor aqueous solubility and moderate permeability of Nelfinavir mesylate (NFM) leads to high variability in absorption after oral administration. To improve the solubility and bioavailability of NFM, the self microemulsifying drug delivery system (SMEDDS) was developed. For this purpose, Quality by design (QbD) approach employing D-optimal mixture design was used to prepare SMEDDS of NFM. Further, the software generated numerically optimized SMEDDS were developed by utilizing desirability function. Maisine 35-1, Tween 80, and Transcutol HP were identified as oil, surfactant, and co-surfactant that had best solubility for NFM. Ternary phase diagrams were plotted to identify the self-emulsification region. Dissolution of putative NFM in simulated fasted or fed small intestinal conditions, respectively, predicted that there is a positive food effect. However, NFM loaded SMEDDS showed absence of food effect with no significant difference in dissolution performance either in Fasted or fed state simulated intestinal fluid (FaSSIF or FeSSIF) biorelevent dissolution media. The prepared SMEDDS were thermodynamically stable with droplet size (121 nm), poly dispersity index (PDI) (0.198) and emulsification time (<1 min). Transmission electron microscopy (TEM) analysis confirmed the spherical shape of the reconstituted SMEDDS droplets. The ex vivo performance revealed 4.57 fold enhancement in the apparent permeability of NFM as compared to NFM suspension. The animal pharmacokinetic analysis in New Zealand strain rabbits indicated food effect on pure NFM suspension. However, absence of food effect and 3.5-3.6 fold enhancement in the oral bioavailability was observed when NFM was formulated into SMEDDS. Thus, it could be envisaged that development of SMEDDS formulation of NFM could be one of the best alternative to enhance oral bioavailability of NFM.

Food Effect in Humans: Predicting the Risk Through In Vitro Dissolution and In Vivo Pharmacokinetic Models

In vitro and in vivo experimental models are frequently used to assess a new chemical entity's (NCE) biopharmaceutical performance risk for food effect (FE) in humans. Their ability to predict human FE hinges on replicating key features of clinical FE studies and building an in vitro-in vivo relationship (IVIVR). In this study, 22 compounds that span a wide range of physicochemical properties, Biopharmaceutics Classification System (BCS) classes, and food sensitivity were evaluated for biorelevant dissolution in fasted- and fed-state intestinal media and the dog fed/fasted-state pharmacokinetic model. Using the area under the curve (AUC) as a performance measure, the ratio of the fed-to-fasted AUC (FE ratio) was used to correlate each experimental model to FE ratio in humans. A linear correlation was observed for the in vitro dissolution-human IVIVR (R (2) = 0.66, % mean square error 20.7%). Similarly, the dog FE ratio correlated linearly with the FE ratio in humans (R (2) = 0.74, % mean square error 16.25%) for 15 compounds. Data points near the correlation line indicate dissolution-driven mechanism for food effect, while deviations from the correlation line shed light on unique mechanisms that can come into play such as GI physiology or unusual physicochemical properties. In summary, fed/fasted dissolution studies and dog PK studies show a reasonable correlation to human FE, hence are useful tools to flag high-risk NCEs entering clinical development. Combining kinetic dissolution, dog FE model and in silico modeling one can study FE mechanism and formulation strategies to mitigate the FE risk.

Prediction of in-vivo pharmacokinetic profile for immediate and modified release oral dosage forms of furosemide using an in-vitro-in-silico-in-vivo approach

OBJECTIVES

To develop a physiologically based pharmacokinetic (PBPK) model for furosemide immediate release (IR) tablets and modified release (MR) capsules by coupling biorelevant dissolution testing results with pharmacokinetic (PK) and physiologic parameters, and to investigate the key factors influencing furosemide absorption using simulation approaches and the PBPK model.

METHODS

Using solubility, dissolution kinetics, gastrointestinal (GI) parameters and disposition parameters, a PBPK model for furosemide was developed with STELLA software. Solubility and dissolution profiles for both formulations were evaluated in biorelevant and compendial media. The simulated plasma profiles were compared with in-vivo profiles using point estimates of area under plasma concentration-time curve, maximal concentration after the dose and time to maximal concentration after the dose.

KEY FINDINGS

Simulated plasma profiles of both furosemide IR tablets and MR capsules were similar to the observed in-vivo profile in terms of PK parameters. Sensitivity analysis of the IR tablet model indicated that both the gastric emptying and absorption rate have an influence on the plasma profile. For the MR capsules, the sensitivity analysis suggested that the release rate in the small intestine, gastric emptying and the absorption rate all have an influence on the plasma profile.

CONCLUSIONS

A predictive model to describe both IR and MR dosage forms containing furosemide was attained. Because sensitivity analysis of the model is able to identify key factors influencing the plasma profile, this in-vitro-in-silico-in-vivo approach could be a useful tool for facilitating formulation development of drug products.

Parameterization of small intestinal water volume using PBPK modeling

To facilitate accurate predictions of oral drug disposition, mechanistic absorption models require optimal parameterization. Furthermore, parameters should maintain a biological basis to establish confidence in model predictions. This study will serve to calculate an optimal parameter value for small intestinal water volume (SIWV) using a model-based approach. To evaluate physiologic fidelity, derived volume estimates will be compared to experimentally-based SIWV determinations. A compartmental absorption and transit (CAT) model, created in Matlab-Simulink®, was integrated with a whole-body PBPK model, developed in PK-SIM 5.2®, to provide predictions of systemic drug disposition. SIWV within the CAT model was varied between 52.5mL and 420mL. Simulations incorporating specific SIWV values were compared to pharmacokinetic data from compounds exhibiting solubility induced non-proportional changes in absorption using absolute average fold-error. Correspondingly, data pertaining to oral administration of acyclovir and chlorothiazide were utilized to derive estimates of SIWV. At 400mg, a SIWV of 116mL provided the best estimates of acyclovir plasma concentrations. A similar SIWV was found to best depict the urinary excretion pattern of chlorothiazide at a dose of 100mg. In comparison, experimentally-based estimates of SIWV within adults denote a central tendency between 86 and 167mL. The derived SIWV (116mL) represents the optimal parameter value within the context of the developed CAT model. This result demonstrates the biological basis of the widely utilized CAT model as in vivo SIWV determinations correspond with model-based estimates.

Novel nelfinavir mesylate loaded d-α-tocopheryl polyethylene glycol 1000 succinate micelles for enhanced pediatric anti HIV therapy: In vitro characterization and in vivo evaluation

Worldwide more than 35 million people are living with Human Immunodeficiency Virus (HIV) where 3.3 million are children. This translates in approximately 700 new daily infections in children only in 2012. Prolonged High Activity Antiretroviral Therapy (HAART) regimes could present low-patient compliance, especially in children, affecting therapeutic success. Nelfinavir mesylate (NFV) is a non-peptidic HIV-1 protease inhibitor (IP) which was the first IP recommended for pediatric use (>2 years-old). It exhibits pH-dependant aqueous solubility which results highly restricted at physiological pH values. The former represents a main clinical limitation due to the reduction on drug absorption along the small intestine after an oral administration, leading to unpredictable drug bioavailability. Moreover a liquid formulation of NFV is not available worldwide, preventing appropriate dose adjustment and more convenient administration. In this framework, the present investigation reports the development of a NFV highly concentrated aqueous formulation for a more appropriate management of pediatric anti-HIV therapy. The aim was to encapsulate NFV within D-α-tocopheryl polyethylene glycol 1000 succinate micelles to improve its aqueous solubility and its oral pharmacokinetic parameters. Results show that NFV aqueous solubility was increased up to 80.3 mg/mL. NFV-loaded micelles exhibited a hydrodynamic diameter of 5.6 nm and a spherical morphology as determined by dynamic light scattering and transmission electronic microscopy, respectively. In vitro NFV release profile demonstrated a cumulative drug release of 56% at 6 h. Finally, in vivo data showed a significant (p<0.01) increase of Area-Under-the-Curve between 0 and 24 h for NFV encapsulated in micelles in comparison with a NFV suspension prepared with glycerin 20% v/v and carboxymethylcellulose sodium 0.5% w/v, representing an increment on drug oral relative bioavailability of 1.71-fold. Thereby, this formulation represents an innovative nanotechnological platform to improve pediatric HIV pharmacotherapy.

Paediatric oral biopharmaceutics: key considerations and current challenges

The complex process of oral drug absorption is influenced by a host of drug and formulation properties as well as their interaction with the gastrointestinal environment in terms of drug solubility, dissolution, permeability and pre-systemic metabolism. For adult dosage forms the use of biopharmaceutical tools to aid in the design and development of medicinal products is well documented. This review considers current literature evidence to guide development of bespoke paediatric biopharmaceutics tools and reviews current understanding surrounding extrapolation of adult methodology into a paediatric population. Clinical testing and the use of in silico models were also reviewed. The results demonstrate that further work is required to adequately characterise the paediatric gastrointestinal tract to ensure that biopharmaceutics tools are appropriate to predict performance within this population. The most vulnerable group was found to be neonates and infants up to 6 months where differences from adults were greatest.

Application of physiologically based absorption modeling to formulation development of a low solubility, low permeability weak base: mechanistic investigation of food effect

Physiologically based pharmacokinetic (PBPK) modeling has been broadly used to facilitate drug development, hereby we developed a PBPK model to systematically investigate the underlying mechanisms of the observed positive food effect of compound X (cpd X) and to strategically explore the feasible approaches to mitigate the food effect. Cpd X is a weak base with pH-dependent solubility; the compound displays significant and dose-dependent food effect in humans, leading to a nonadherence of drug administration. A GastroPlus Opt logD Model was selected for pharmacokinetic simulation under both fasted and fed conditions, where the biopharmaceutic parameters (e.g., solubility and permeability) for cpd X were determined in vitro, and human pharmacokinetic disposition properties were predicted from preclinical data and then optimized with clinical pharmacokinetic data. A parameter sensitivity analysis was performed to evaluate the effect of particle size on the cpd X absorption. A PBPK model was successfully developed for cpd X; its pharmacokinetic parameters (e.g., C max, AUCinf, and t max) predicted at different oral doses were within ±25% of the observed mean values. The in vivo solubility (in duodenum) and mean precipitation time under fed conditions were estimated to be 7.4- and 3.4-fold higher than those under fasted conditions, respectively. The PBPK modeling analysis provided a reasonable explanation for the underlying mechanism for the observed positive food effect of the cpd X in humans. Oral absorption of the cpd X can be increased by reducing the particle size (<100 nm) of an active pharmaceutical ingredient under fasted conditions and therefore, reduce the cpd X food effect correspondingly.