Forecasting the in vivo performance of four low solubility drugs from their in vitro dissolution data

In vitro controlled release of vinpocetine-cyclodextrin-tartaric acid multicomponent complexes from HPMC swellable tablets

The objective of this study was to investigate the effect of multicomponent complexation (MCC) of vinpocetine (VP), a poorly soluble base-type drug, with beta-cyclodextrin (betaCD), sulfobutylether beta-cyclodextrin (SBEbetaCD), tartaric acid (TA), polyvinylpyrrolidone (PVP) and hydroxypropylmethylcellulose (HPMC), on the design of controlled release hydrophilic HPMC tablets and to evaluate their in vitro release profiles by a pH gradient method. Multicomponent complexation led to enhanced dissolution properties of VP both in simulated gastric and intestinal fluids, and became possible the development of HPMC tablet formulations with more independent pH dissolution profiles. Drug release process was investigated experimentally using USP apparatus 3 and by means of model-independent parameters. Responses studied included similarity of dissolution profiles, time for 60% of the drug to dissolve (T(60%)), percent of VP released after 7 h (PD(7 h)) and the dissolution efficiency parameter at 12 h (DE(12 h)). Influence of multicomponent complexation was proved to increase the release of VP from HPMC tablets and superior PD(7 h) and DE(12 h) values were obtained in formulations containing VP-CD-TA complexes. Results supported the use of HPMC matrices to provide a useful tool in retarding the release of VP and that dissolution characteristics of the drug may be modulated by multicomponent complexation in these delivery systems, suggesting an improvement on VP bioavailability.

Media to simulate the postprandial stomach I. Matching the physicochemical characteristics of standard breakfasts

To better predict food effects on the bioavailability/bioequivalence of drugs and drug products from in-vitro data, a dissolution medium that simulates the initial composition of the postprandial stomach was developed. First, the physical parameters of two homogenized standard breakfasts often administered to assess food effects in pharmacokinetic studies were measured. These included pH, buffer capacity, osmolality, surface tension and viscosity. Subsequently, the match of the physical parameters of several commercially available liquid meals, including long-life milk, Ensure and Ensure Plus to those of the breakfasts was evaluated. Of the three liquid meals studied, Ensure Plus had the closest physicochemical behaviour to that of homogenized standard breakfasts. By increasing the viscosity of Ensure Plus with 0.45% pectin, it was possible to obtain a medium that closely resembles the FDA standard breakfast.

Characterization of an active pharmaceutical ingredient by its dissolution properties: amoxicillin trihydrate as a model drug

To characterize the dissolution of particles, a dissolution rate coefficient alpha, consisting of a geometric factor gamma and material constant mu, was introduced. The impact of the particle geometry on the initial rate of dissolution was assessed for spherical, cubic and tetrahedral particles. Additionally, a description of dissolution of samples containing multiple populations of particles was derived. A two-population model was employed to characterize sieved fractions of amoxicillin trihydrate. The investigation, using factor analysis, of the influence of dose, particle size and agitation intensity on the dissolution rate coefficient alpha indicated the presence of disintegrating agglomerates in larger particles. Based on the dissolution characteristics of particular particle size fractions and on the determined particle size distribution, the dissolution profile of the mixed sample containing nine sieved fractions in size was successfully predicted. Finally, the limitations of the film theory are discussed in light of the multiple-population dissolution theory.

Predicting the precipitation of poorly soluble weak bases upon entry in the small intestine

Solubility and dissolution relationships in the gastrointestinal tract can be critical for the oral bioavailability of poorly soluble drugs. In the case of poorly soluble weak bases, the possibility of drug precipitation upon entry into the small intestine may also affect the amount of drug available for uptake through the intestinal mucosa. To simulate the transfer out of the stomach into the intestine, a transfer model was devised, in which a solution of the drug in simulated gastric fluid is continuously pumped into a simulated intestinal fluid, and drug precipitation in the acceptor medium is examined via concentration-time measurements. The in-vitro precipitation of three poorly soluble weakly basic drugs, dipyridamole, BIBU 104 XX and BIMT 17 BS, was investigated. For all three, extensive supersaturation was achieved in the acceptor medium. Under simulated fasted-state conditions, precipitation occurred for all three compounds whereas under simulated fed-state conditions, the higher concentrations of bile components and the lower pH value in the acceptor medium inhibited precipitation at concentrations corresponding to usual doses in all cases. Comparison with pharmacokinetic data indicated that a combination of transfer model data with solubility and dissolution profiles should lead to better predictions of in-vivo behaviour of poorly soluble weak bases.

Dissolution media simulating the intralumenal composition of the small intestine: physiological issues and practical aspects

The objective of this study was to test various aspects of dissolution media simulating the intralumenal composition of the small intestine, including the suitability of the osmolality-adjusting agents and of the buffers, the substitution of crude sodium taurocholate (from ox bile) for pure sodium taurocholate and the substitution of partially hydrolysed soybean phosphatidylcholine for egg phosphatidylcholine. It was concluded that biorelevant media should contain sodium as the major cation species to better reflect the physiology. However, the use of non-physiologically relevant buffers is inevitable, especially for simulation of the fed state in the small intestine. The buffers used may affect the solubility product of weakly basic compounds with pK(a)(s) higher than about 5, the solubility of extremely highly lipophilic compounds due to salting in/out properties of the anion of the buffer and the stability of the dissolving compound. It is prudent in relevant situations to run an additional dissolution test in a modified fed state simulated intestinal fluid (FeSSIF) (or fasted state simulated intestinal fluid (FaSSIF), where applicable) containing alternative buffer species. Although a mixture of bile salts is physiologically more relevant than pure sodium taurocholate, this issue seems to be of practical importance in only a few cases. Adequate simulations in these cases will probably require the use of a number of pure substances and could substantially increase the cost of the test. Finally, unless the drug is extremely lipophilic (ca. logP> 5), egg phosphatidylcholine can be substituted by partially hydrolysed soybean phosphatidylcholine.

Development and evaluation of bio-dissolution systems capable of detecting the food effect on a polysaccharide-based matrix system

Methods are proposed and tested for mimicking the in vitro food effect on controlled release dosage forms, using USP dissolution apparatus 3. Using in vivo data a pH and time profile was constructed, and the methods utilized either presoaking in peanut oil or continuous oil contact to mimic the presence of a high fat meal. A water soluble drug (propranolol hydrochloride, class 1 by BCS) was used as a model material. Both methods were able to confirm that a labile multiparticulate system (Inderal LA) was susceptible to such in vitro effects. A hydrocolloid matrix tablet showed low susceptibility to either technique. There was a good correlation between methods, which may indicate that the oil presoaking method, which is less time consuming to carry out and leads to more simple subsequent analysis, may be sufficient to identify dosage forms susceptible to physical food effects.

Comparison of simulated cumulative drug versus time data sets with indices

The objectives of this study were twofold. First, to clarify the applicability of the similarity factor, f(2), the difference factor, f(1), and the Rescigno index, xi(i), in the comparison of cumulative drug vs. time data sets. Second, to assess the possibility for these indices to be used on a confidence interval basis. Theoretical profiles as well as errorless and errant cumulative % data sets were simulated using the Weibull function. At various variability levels, 12-fold and 3-fold replicated reference and test data sets were generated from the errant data sets. The 90% confidence intervals were constructed for the median of the index (non-parametric confidence intervals, NPCIs) and for the evaluated index based on the 5th and 95th percentiles of 1000 index values estimated from bootstrapped samples (bootstrapped confidence intervals, BSCIs). It was observed that at low variability levels, i.e. when mean data sets can be used, all indices could be used for the comparison of cumulative data sets. At high variability levels, only the BSCIs of f(2) included the actual index value for the 12-fold replicated data sets. However, deviations of the low limits of NPCIs of f(2) from the actual index values were similar to corresponding deviations of BSCIs. When 3-fold replicated data sets were used, both NPCIs and BSCIs of all indices were generally reliable but much larger than that of 12 replications. In conclusion, the time period for the evaluation of the indices cannot be theoretically justified because indices change continuously with time. Cutoff points for their evaluation must be decided on a case-by-case basis. If theoretically possible, evaluation of the indices should be done by using areas. With highly variable data, BSCIs are preferred because compared to NPCIs they are less dependent on the number of replications. When n=12, BSCIs of f(2) are comparatively more reliable. When n=3, BSCIs of the indices tested in this study have similar performances.

Can the USP paddle method be used to represent in-vivo hydrodynamics?

Experiments in-vitro and in dogs were conducted to find in-vitro hydrodynamic conditions that can be used to represent gastrointestinal motility patterns. Specifically, the dissolution performance of micronised and coarse-grade felodipine (a poorly soluble, neutral, lipophilic drug) was studied in a biorelevant medium in the USP paddle apparatus at various paddle speeds. Ratios of percentage dissolved (slower:faster rev min(-1)) were calculated pairwise. These ratios were then compared with AUC ratios obtained in a corresponding pharmacokinetic study in Labradors, in which the absorption of both the micronised and coarse-grade felodipine had been compared under two gastrointestinal hydrodynamic conditions. Using a paddle speed combination of 75 and 125 rev min(-1) to represent the motility patterns in response to administration of normal saline and 5% glucose, respectively, the in-vitro ratios (75:125 rev min(-1) dissolution ratio was 91% for the micronised and 46% for the coarse-grade powder) showed good agreement with the pharmacokinetic data (saline-to-glucose absorption ratio was 98% for the micronised and 46% for the coarse-grade powder). It was concluded that, provided an appropriate composition is chosen for the dissolution test, the USP paddle apparatus can be used to reflect variations in hydrodynamic conditions in the upper gastrointestinal tract.

On the assessment of effects of food on the pharmacokinetics of drugs in early development

The impact of food on the pharmacokinetics of a drug has important implications in drug development. This commentary is aimed at addressing two key challenges, developability of drugs whose pharmacokinetics are severely influenced by food, and the need for addressing the effects of fruit juice ingredients which modulate metabolic/efflux properties of a compound. Perspectives on the value in predicting food-drug interactions during preclinical development, timing of clinical food-drug interaction studies, and implications of food effects are presented herein.

In vitro assessment of oral lipid based formulations

In recent years there has been an increase in interest in the utility of lipid based delivery systems, at least in part as a result of the effective development of lipid based products such as Sandimmun Neoral (cyclosporin), Norvir (ritonavir) and Fortovase (saquinavir). The development pathway for lipid based formulations, however, is still largely empirical, and in vitro models that are predictive of oral bioavailability enhancement are lacking. The use of modified dissolution media, reflecting the bile salt and phospholipid levels in the intestine, has met with some success in terms of the ability to predict the bioavailability of poorly water soluble drugs and the potential bioavailability enhancing effects of food. These approaches, however, do not have the flexibility or complexity to deal with the interactions inherent in the digestion, dispersion and solubilisation of a lipid based formulation and the coincident dissolution profile of a co-administered drug. In this review, the utility of modified dissolution media to predict the impact of food on the absorption of poorly water soluble, lipophilic drugs, is explored. These dissolution based systems are subsequently contrasted with the use of lipid digestion models which have found increasing application in assessment of the interaction of digestible dose forms with the gastrointestinal milieu.

Biorelevant dissolution testing to predict the plasma profile of lipophilic drugs after oral administration

PURPOSE

To quantitatively compare in vitro dissolution data in biorelevant and compendial media, to investigate whether in vitro differences are reflected in the simulated plasma profile and to specify under which circumstances prediction of the plasma profile of orally administered lipophilic drugs can be achieved.

METHODS

Previously published dissolution data from seven products of four lipophilic drugs were compared using the first order model, the RRSBW distribution, and a model based on the Noyes-Whitney theory. Simulated plasma profiles were then obtained using a model-dependent approach. Simulated and observed plasma profiles were compared with the difference factor, f1.

RESULTS

No model consistently provided the best fit to the in vitro data, which varied significantly with medium composition. Prediction of the plasma profile was possible (9.6 < or = f1 < or = 34.2) in seven out of eleven cases.

CONCLUSIONS

Although prediction of the plasma profile of lipophilic drugs solely on the basis of in vitro data remains an ambitious target, this study shows that the plasma profile of a lipophilic drug can be predicted with appropriate in vitro dissolution data, provided that the absolute bioavailability of the drug is known and the drug has dissolution limited absorption.

Wetting behavior of bile salt-lipid dispersions and dissolution media patterned after intestinal fluids

The wetting properties of bile salt-lipid solutions and dispersions patterned after the contents of the upper intestine in the fed and fasted states were evaluated using poly(methyl methacrylate) (PMMA) as a model substrate. The surface tension of the solutions and their contact angles on PMMA were measured. Media compositions for the intestinal fed and fasted states were estimated on the basis of physiologic data. The effect of various individual lipids and media composition was also evaluated relative to the adhesional, immersional, and spreading stages of wetting. In micellar systems, both the type and concentration of lipid present in the bile salt solution had an influence on wetting. The wetting of media patterned after gastrointestinal contents showed marked differences with respect to the fed or fasted state compositions. For the fed state compositions, alteration of the solution pH from 7.5 to 5.0 resulted in a significant change in wetting. The surface tension of the medium representative of the fasted state was 15 mN/m higher than that of the fed state. The wetting properties of the physiologically representative media formulated in this study were markedly different compared with other media proposed in the literature. Analysis of the wetting behavior of individual lipids as a function of concentration in bile salt solutions showed that they adsorb in a manner that progressively reduces the expected wetting of the surface. The results have implications for the design and formulation of both biorelevant and surfactant-based dissolution media.

In vitro-in vivo correlations for lipophilic, poorly water-soluble drugs

Although several routes of administration can be considered for new drug entities, the most popular remains the oral route. To predict the in vivo performance of a drug after oral administration from in vivo data, it is essential that the limiting factor to absorption can be modelled in vitro. In the case of BCS class II drugs dissolution is rate-limiting to absorption, so the use of biorelevant dissolution tests can be used to predict differences in bioavailability among different formulations and dosing conditions. To achieve an a priori correlation, the composition, volume and hydrodynamics of the contents in the gastrointestinal lumen following administration of the dosage form must be accurately simulated. Four media have been chosen/developed to model composition of the gastric and intestinal contents before and after meal intake. These are SGF, milk, FASSIF and FeSSIF, which model fasted and fed state conditions in the stomach and small intestine respectively. Using these media, excellent correlations have been obtained with the following poorly soluble drugs: danazol, ketoconazole, atovaquone and troglitazone. In all cases, fed vs. fasted state effects can be predicted from dissolution data and, where several formulations were available for testing, dissolution tests could also be used to determine which would have the best in vivo performance.