Qualification of In Vitro Dissolution Absorption System 2 (IDAS2) with Caco-2 and MDCK Cell Monolayers: Dose Sensitivity Study Using BCS Class I and III Drugs.

This study aimed to validate the In vitro Dissolution Absorption System 2 (IDAS2) containing a biological barrier of Caco-2 or Madin-Darby canine kidney (MDCK) cell monolayer through dose sensitivity studies. Metoprolol and propranolol were selected as Biopharmaceutics Classification System (BCS) Class I model drugs, and atenolol as a Class III model drug. The IDAS2 is comprised of a dissolution vessel (500 mL) and two permeation chambers (2 × 8.0 mL) mounted with Caco-2 or MDCK cell monolayer. One or two immediate-release tablet(s) of the model drug were added to the dissolution vessel, and the time profiles of dissolution and permeation were observed. Greater than 85% of metoprolol and propranolol (tested at two dosing concentrations) were dissolved by 15 min, and all drugs were fully dissolved by 30 min. All three drugs were more permeable across Caco-2 cells than MDCK cells with a linear increase in permeation across both cells at both dose concentrations. Thus, the dose sensitivity of the IDAS2 was demonstrated using both cell barriers. These results indicate a successful qualification of IDAS2 for the development/optimization of oral formulations and that MDCK cells can be utilized as a surrogate for Caco-2 cells.

Effects of Ingested Water Volume on Oral Absorption of Fenofibrate, a BCS Class II Drug, from Micronized and Amorphous Solid Dispersion Formulations in Rats.

In this study, we investigated the effects of ingested water volume on the oral absorption of fenofibrate (FEN) with several formulations to confirm the applicability of rats for oral formulation screening. Oral absorption of suspended crystalline FEN was significantly improved by increasing ingested water volume (from 0.5 to 2 mL). FEN absorption improvement by particle size reduction and the linearity in oral absorption by dose escalation suggested that the rate-limiting step of FEN absorption in rats was the dissolution rate, consistent with that in humans. When FEN, as an amorphous solid dispersion (ASD) formulation, was suspended in water followed by immediate administration, oral FEN absorption was significantly higher than when administered in crystalline form and was not influenced by the differences in ingested water volume. Oral absorption of FEN from encapsulated ASD formulation in 1 or 2 mL of water was comparable with that of the suspension form. However, 0.5 mL of water significantly reduced the oral absorption of the solid ASD FEN formulation. These results indicate that to improve the oral absorption of poorly water-soluble drugs when performing a preclinical study with rats, 1 mL of water is the minimum preferable ingested volume to evaluate in vivo formulation performance.

Maximizing the Oral Bioavailability of Poorly Water-Soluble Drugs Using Novel Oil-Like Materials in Lipid-Based Formulations.

Lipid-based formulations, such as self-microemulsifying drug-delivery systems (SMEDDSs), are promising tools for the oral delivery of poorly water-soluble drugs. However, failure to maintain adequate aqueous solubility after coming into contact with gastrointestinal fluids is a major drawback. In this study, we examined the use of a novel cinnamic acid-derived oil-like material (CAOM) that binds drugs with a high affinity through π-π stacking and hydrophobic interactions, as an oil core in a SMEDDS for the oral delivery of fenofibrate in rats. The use of the CAOM in the SMEDDS resulted in an unprecedented enhancement in fenofibrate bioavailability, which exceeded the bioavailability values obtained using SMEDDSs based on corn oil, a conventional triglyceride oil, or Labrasol, an enhancer of intestinal permeation. Further characterization revealed that the CAOM SMEDDS does not alter the intestinal permeability and has no inhibitory activity on P-glycoprotein-mediated drug efflux. The results reported herein demonstrate the strong potential of CAOM formulations as new solubilizers for the efficient and safe oral delivery of drugs that have limited water solubility.

Impact of Dietary Intake of Medium-Chain Triacylglycerides on the Intestinal Absorption of Poorly Permeable Compounds.

The present study sought to demonstrate the effect of dietary intake of medium-chain triacylglycerides (MCTs) on the intestinal absorption of a poorly permeable compound of intermediate molecular weight (FITC-dextran 4000 [FD-4]). As a model of MCTs, C8-C12 fatty acid triacylglyceride (COCONAD ML) was mainly used, and the dose strength of each triglyceride was set with consideration of the dietary ingestion dose (12.5 mg/rat). When FD-4 with MCTs dispersed in fasted state simulated intestinal fluid containing surfactants was administered into the rat jejunum, the intestinal absorption of FD-4 was significantly higher than when administered with a similar solution with or without corn oil (long-chain triglycerides). The effects of pretreatment by MCT lipolysis, inhibition of endogenous lipases, and different dose timings of MCTs and FD-4 on the intestinal absorption of FD-4 indicated that medium-chain fatty acids, such as caprylic acid and capric acid, released from MCTs by lipolysis in the small intestine significantly enhanced the intestinal absorption of FD-4, but the effect was transient. In addition, a similar effect was observed when MCTs were dispersed in soymilk, although large interindividual variation was detected. These findings suggested that dietary intake of MCTs might affect the intestinal absorption of poorly permeable compounds.

Interaction with Mixed Micelles in the Intestine Attenuates the Permeation Enhancing Potential of Alkyl-Maltosides.

The purpose of the present study was to investigate the interaction of intestinal permeation enhancers with lipid and surfactant components present in the milieu of the small intestine. Maltosides of different chain lengths (decyl-, dodecyl-, and tetradecyl-maltoside; DM, DDM, TDM, respectively) were used as examples of nonionic, surfactant-like permeation enhancers, and their effect on the permeation of FD4 across Caco-2 monolayers was monitored. To mimic the environment of the small intestine, modified versions of fasted and fed state simulated intestinal fluid (FaSSIFmod, FeSSIFmod6.5, respectively) were used in addition to standard transport media (TM). Compared to the buffer control, 0.5 mM DDM led to a 200-fold permeation enhancement of FD4 in TM. However, this was dramatically decreased in FaSSIFmod, where a concentration of 5 mM DDM was necessary in order to elicit a moderate, 4-fold, permeation enhancement. Its capacity to promote permeation was diminished further when FeSSIFmod6.5 was employed. Even when cells were exposed to a concentration of 5 mM, no significant permeation enhancement of FD4 was observed. Analogous effects were observed in the case of DM and TDM, with slight deviations on account of differences in their critical micelle concentration (CMC). This observation was corroborated by calculating the amount of maltoside monomer versus micellar bound maltoside in FaSSIFmod and FeSSIFmod6.5, which demonstrated a reduced amount of free monomer in these fluids. To evaluate the in vivo significance of our findings, DDM solutions in TM, FaSSIFmod, and FeSSIFmod6.5 were used for closed intestinal loop studies in rats. Consistent with the results found in in vitro permeation studies, these investigations illustrated the overwhelming impact of sodium taurocholate/lecithin micelles on the permeation enhancing effect of DDM. While DDM led to a 20-fold increase in FD4 bioavailability when it was applied in TM, no significant permeation enhancement was seen in FaSSIFmod/FeSSIFmod6.5. Collectively, these investigations highlight the importance of using biorelevant media when evaluating the potency of permeation enhancers. In doing so, this ensures improved correlations between in vitro and in vivo studies and thus enables an early and more accurate assessment of promising permeation enhancers.

In vitro-in vivo correlation of the effect of supersaturation on the intestinal absorption of BCS Class 2 drugs.

The aim of this study was to establish an in vitro method for evaluating the effect of supersaturation on oral absorption of poorly water-soluble drugs in vivo. Albendazole, dipyridamole, gefitinib, and ketoconazole were used as model drugs. Supersaturation of each drug was induced by diluting its stock solution by fasted state simulated intestinal fluid (FaSSIF) (solvent-shift method), then dissolution and precipitation profile of the drug was observed in vitro. The crystalline form of the precipitate was checked by differential scanning calorimetry (DSC). For comparison, control suspension was prepared by suspending a drug powder directly into FaSSIF (powder-suspending method). In vivo intestinal absorption of the drug was observed in rats by determined the plasma concentration after intraduodenal administration of drug suspensions. For all drugs, suspensions prepared by solvent-shift method showed significantly higher dissolved concentration in vitro than that prepared by powder-suspending method, clearly indicated the induction of supersaturation. DSC analysis revealed that crystalline form of the precipitate profoundly affects the extent and the duration of supersaturation. A rat in vivo study confirmed that the supersaturation of these drugs increased the fraction absorbed from the intestine, which corresponded well to the in vitro dissolution and precipitation profile of drugs except for ketoconazole. For ketoconazole, an in vivo absorption study was performed in rats pretreated with 1-aminobenzotriazole, a potent inhibitor of CYP mediated metabolism. CYP inhibition study suggested that the high luminal concentration of ketoconazole caused by supersaturation saturated the metabolic enzymes and further increased the systemic exposure of the absorbed drug. The additional effects of supersaturation on the absorption of ketoconazole are consistent with previous studies in humans under differing gastric pH conditions. In conclusion, effects of supersaturation on the intestinal absorption of poorly water-soluble drugs could be predicted from in vitro dissolution and a precipitation study. However if supersaturation affects the pharmacokinetic profiles of drugs, such as a first-pass metabolism, a combination with in vivo study should be required to evaluate its impact on oral bioavailability.

Near-infrared imaging of in vivo performance of orally administered solid forms to rats: Feasibility study with indocyanine green.

This study demonstrates the applicability of near-infrared (NIR) imaging to evaluating in vivo oral formulation performance. As a NIR probe and model drug, indocyanine green (ICG) and acetaminophen (ACE) were selected, respectively. The fluorescence intensity of ICG greatly increased upon dissolution, with the dissolved ICG passing through the gastrointestinal tract over time. Both compounds (0.05 mg of ICG and 0.5 mg of ACE) were encapsulated in gelatin and hydroxypropyl methylcellulose (HPMC) capsules in the solid form. In vitro, the HPMC capsules showed a disintegration lag time, a feature that was not observed for the gelatin capsules. After oral administration of each capsule to rats, blood samples were collected, followed by fluorescent imaging of the abdominal region. At 0.25 h after HPMC capsule administration, the fluorescence area and intensity were significantly small and relatively weak compared to that of the gelatin capsule. These tendencies resulted from the difference in capsule disintegration times, leading to a change in gastric emptying, which corresponded well with the initial time profile of the plasma concentration of ACE. These results indicate that possibility of NIR imaging with ICG to evaluate in vivo performance of orally administered formulations.

Measurement of drug concentration in the stomach after intragastric administration of drug solution to healthy volunteers: analysis of intragastric fluid dynamics and drug absorption.

PURPOSE: To evaluate the time-profile of intragastric fluid volume in humans after intragastric administration of drug solution. METHODS: Eight healthy volunteers were intragastrically administered 150 mL of drug solution containing atenolol (non-absorbable marker) and salicylic acid, then, aliquots of gastric fluid (ca. 2 mL) were sampled for 2 h through the catheter. Rate constants for secretion and emptying of the fluid were obtained by fitting the time-course of atenolol concentration to the simple gastric fluid transit model. Absorption of salicylic acid from the stomach was estimated by comparing its gastric concentration with that of atenolol. RESULTS: Kinetic analysis of atenolol concentration in the stomach indicated a rapid emptying of the fluid with an average half-life of 4.2 min. Steady-state intragastric fluid volume in 8 volunteers was estimated as 4-133 mL with an average of 42 mL. Intragastric concentration (normalized by dose) of salicylic acid was always lower than that of atenolol, showing approximately 40% of salicylic acid was absorbed from the stomach before emptying to the intestine. CONCLUSIONS: This study provided valuable information on intragastric fluid dynamics and gastric drug absorption in humans to establish a better in vitro-in vivo correlation in oral drug absorption.

The effects of degree and duration of supersaturation on in vivo absorption profiles for highly permeable drugs, dipyridamole and ketoconazole.

The prediction of oral absorption from a supersaturating drug delivery system (SDDS) remains a significant challenge. Here we evaluated the effects of the degree and duration of supersaturation on in vivoabsorption for dipyridamole and ketoconazole. Various dose concentrations of supersaturated suspensions were prepared by a pH shift method, and in vitro dissolution and in vivo absorption profiles were determined. For dipyridamole, the duration of supersaturation decreased with the increase of the dose concentration owing to rapid precipitation. For ketoconazole, the initially constant dissolved concentrations due probably to the liquid-liquid phase separation (LLPS) as a reservoir were observed at high dose concentrations. However, the LLPS did not delay the peak plasma concentration of ketoconazole in rats, indicating that drug molecules were immediately released from the oil phase to the bulk aqueous phase. For both model drugs, the degree of supersaturation, but not the duration of supersaturation, correlated with systemic exposure, indicating quick drug absorption before precipitation. Therefore, the degree of supersaturation is an important parameter compared with the duration of supersaturation for enhancing the in vivo absorption of highly permeable drugs. These findings would help develop a promising SDDS.

The impact of surface area per volume (SA/V) ratio on drug transport from supersaturated solutions of ketoconazole.

The purpose of this study aimed to evaluate the impact of the surface area per volume (SA/V) ratio on drug transport from two supersaturated solutions (SSs) of ketoconazole with and without hydroxypropyl methylcellulose (HPMC), used as a precipitation inhibitor. In vitro dissolution, membrane permeation with two SA/V ratios, and in vivo absorption profiles for both SSs were determined. For the SS without HPMC, a two-step precipitation process due to the liquid-liquid phase separation was observed; the constant concentration with approximately 80 % of the dissolved amount was maintained for the first 5 min and subsequently decreased between 5 and 30 min. For the SS with HPMC, a parachute effect was observed; the constant concentration with approximately 80 % dissolved amount was maintained for more than 30 min and decreased very slowly thereafter. Assessment of the SA/V ratio using in vitro and in vivo models demonstrated that when the SA/V ratio was small, the SS with HPMC resulted in a significantly higher permeated amount than the SS without HPMC. In contrast, when the SA/V ratio was large, the HPMC-mediated parachute effect on drug transport from SSs was attenuated, both in vitro and in vivo. The parachute effect by HPMC decreased as the SA/V ratio increased, and the performance of supersaturating formulations would be overestimated by in vitro studies with small SA/V ratios.