Gastrointestinal transfer: In vivo evaluation and implementation in in vitro and in silico predictive tools

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.

Effects of gastric pH on oral drug absorption: In vitro assessment using a dissolution/permeation system reflecting the gastric dissolution process

The aim of the present study was to evaluate the effects of gastric pH on the oral absorption of poorly water-soluble drugs using an in vitro system. A dissolution/permeation system (D/P system) equipped with a Caco-2 cell monolayer was used as the in vitro system to evaluate oral drug absorption, while a small vessel filled with simulated gastric fluid (SGF) was used to reflect the gastric dissolution phase. After applying drugs in their solid forms to SGF, SGF solution containing a 1/100 clinical dose of each drug was mixed with the apical solution of the D/P system, which was changed to fasted state-simulated intestinal fluid. Dissolved and permeated amounts on applied amount of drugs were then monitored for 2h. Similar experiments were performed using the same drugs, but without the gastric phase. Oral absorption with or without the gastric phase was predicted in humans based on the amount of the drug that permeated in the D/P system, assuming that the system without the gastric phase reflected human absorption with an elevated gastric pH. The dissolved amounts of basic drugs with poor water solubility, namely albendazole, dipyridamole, and ketoconazole, in the apical solution and their permeation across a Caco-2 cell monolayer were significantly enhanced when the gastric dissolution process was reflected due to the physicochemical properties of basic drugs. These amounts resulted in the prediction of higher oral absorption with normal gastric pH than with high gastric pH. On the other hand, when diclofenac sodium, the salt form of an acidic drug, was applied to the D/P system with the gastric phase, its dissolved and permeated amounts were significantly lower than those without the gastric phase. However, the oral absorption of diclofenac was predicted to be complete (96-98%) irrespective of gastric pH because the permeated amounts of diclofenac under both conditions were sufficiently high to achieve complete absorption. These estimations of the effects of gastric pH on the oral absorption of poorly water-soluble drugs were consistent with observations in humans. In conclusion, the D/P system with the gastric phase may be a useful tool for better predicting the oral absorption of poorly water-soluble basic drugs. In addition, the effects of gastric pH on the oral absorption of poorly water-soluble drugs may be evaluated by the D/P system with and without the gastric phase.

In-vitro evaluation of performance of solid immediate release dosage forms of weak bases in upper gastrointestinal lumen: experience with miconazole and clopidogrel salts

Objectives

Evaluate the impact of salt and counterion identity on performance of solid immediate release dosage forms of miconazole and clopidogrel, respectively, in fasted upper gastrointestinal lumen using in-vitro methodologies.

Methods

Two miconazole chemical forms (free base and nitrate salt) and three clopidogrel chemical forms (bisulfate, besylate and hydrochloride salts) were studied. Solubilities of miconazole forms were measured in simulated gastric fluids. Gastrointestinal transfer of the five chemical forms was evaluated by using a flow-through, three-compartmental set-up. Precipitation in duodenal compartment was evaluated by using solutions in gastric compartment.

Key findings

Solubilities in simulated gastric fluids, concentrations in duodenal compartment and solubilities in duodenal compartment indicated poorer performance of miconazole nitrate vs. miconazole free base in upper gastrointestinal lumen. In line with the low crystallization tendency of free base, duodenal precipitation of miconazole from a free base solution was limited. Concentrations in duodenal compartment indicated that counterion identity does not affect the performance of clopidogrel; precipitation in duodenal compartment was extensive in all cases.

Conclusions

Miconazole data indicate that salts may adversely affect performance of immediate release dosage forms of weak bases. In line with existing in-vivo data, clopidogrel data indicate that counterion identity is unimportant for the performance of clopidogrel salts in upper intestinal lumen.