In vitro-in vivo correlation in the effect of cyclodextrin on oral absorption of poorly soluble drugs.

In this study the concentration effect of 2-Hydroxypropyl-beta-cyclodextrin (HP-ßCyD) on oral drug absorption of the BCS class II drugs Danazol (DNZ) and Albendazole (ABZ) was evaluated. In vitro permeation of solutions and suspension systems was compared with their in vivo intestinal absorption in rats and their in vitro-in vivo correlation assessed. In solutions excess amounts of HP-ßCyD decreased both in vitro permeation and in vivo absorption due to the decrease in free drug concentration, as expected. However, in suspension systems the contribution of HP-ßCyD by drug complexation was found to be altered by further rate limiting steps for membrane permeation and intestinal absorption of each drug. In vitro permeation of DNZ was rate-limited by the diffusion into the unstirred water layer (UWL), while that of ABZ was rate-limited by the permeation across the lipid membrane. For the in vivo intestinal absorption, both drugs were rate-limited by the dissolution rate from undissolved drug. These differences in the rate-limiting process were considered to cause discrepancies in the result of in vitro and in vivo assays. In conclusion, it is quite important to understand the rate limiting process of oral absorption of the target drug for designing oral liquid formulations containing cyclodextrins.

Importance of free water in controlling granule and tablet properties in a novel granulation method, green fluidized bed granulation (GFBG).

In the pharmaceutical field, green fluidized bed granulation (GFBG) is a novel and eco-friendly manufacturing technology used to produce desired granules via simple blending and spraying steps at ambient temperature using a standard fluidized bed granulator. However, the relations between water content and granule and tablet qualities have not yet been elucidated for GFBG. The purpose of this study was to elucidate the influence of different water quantities used in the GFBG process on granule and tablet qualities. In addition, results from the GFBG process were compared with those from the moisture-activated dry granulation (MADG) process. In terms of tablet tensile strength and disintegration time, GFBG had a wider acceptable range for added water quantity (2.0-5.0%) than did MADG. For all added water quantities, the GFBG granules were within the upper limit of water activity (a surrogate of free water amount), which was 0.61 for tensile strength and 0.55 for disintegration time. The air flow in the GFBG process may have reduced the excess free water on the granules during the absorption process. It was concluded that as compared with MADG, GFBG may be a more robust process for manufacturing granules and tablets with superior properties.

Application of an In Vitro Dissolution/Permeation System to Early Screening of Oral Formulations of Poorly Soluble, Weakly Basic Drugs Containing an Acidic pH-Modifier.

This study aimed to evaluate the usefulness of the dissolution/permeation system (D/P system) as an in vitro tool for early screening of oral formulations of weakly basic drugs containing an acidic pH-modifier. Dipyridamole, having a prominent pH-dependent solubility, was used as a model drug, and various granules containing different amounts of fumaric acid were prepared. Prepared granules were administered orally to hypochlorhydria model rats. It was confirmed that fumaric acid improved the absorption of dipyridamole depending on its amount in the granules. Separately, dissolution and permeation of dipyridamole were observed in vitro in the D/P system. When using a medium with a low buffer capacity which mimicked the human intestinal fluid, rank order of the permeated amount of dipyridamole from various granules in the D/P system did not correlate with its absorption in hypochlorhydric rats. In contrast, when applying a medium with high buffer capacity, the permeated amount in the D/P system well reflected the effects of fumaric acid on the in vivo absorption of dipyridamole. In conclusion, by setting appropriate experimental protocols according to the properties of test compounds and formulations, D/P system can be a potent in vitro tool to predict in vivo performance of oral formulations.

Development of pH-Independent Drug Release Formulation Using Lipocalin-Type Prostaglandin D Synthase.

The purpose of this study was to develop a pH-independent drug release formulation using lipocalin-type prostaglandin D synthase, a member of the lipocalin superfamily, with the function of forming complexes together with various small lipophilic molecules. Dipyridamole, a poorly water-soluble drug, showing a pH-dependent solubility profile, was used as the model drug. The solubilization of dipyridamole was achieved by a simple complex formulation method with lipocalin-type prostaglandin D synthase. The complex formulation was produced successfully by spray drying, and the obtained powder formulation showed complete dissolution in fasted-state simulated gastric fluid (pH, 1.6) and phosphate-buffered solution (pH, 6.8). In addition, the potential stability of the complex formulation was assessed, and the dissolution profile of the produced powder at pH 6.8 was maintained after 4-week storage under several storage conditions. Furthermore, a pharmacokinetic study using hypochlorhydria model rats was performed to verify the improvement of the intestinal absorption behavior, and eventually the complex formulation overcame the problematic absorption profile of dipyridamole in the elevated gastric pH conditions. These results, taken together, demonstrate that the use of this well-designed drug-delivery carrier is feasible for the development of pH-independent drug release formulations.

Novel oral formulation approach for poorly water-soluble drug using lipocalin-type prostaglandin D synthase.

Lipocalin-type prostaglandin D synthase (L-PGDS), a member of the lipocalin superfamily, possesses the function of forming complexes together with various small lipophilic molecules. In this study, we chose telmisartan as a model drug due to its pH dependent poor water solubility, and developed and characterized a novel solubilized formulation of telmisartan using a complex formulation with L-PGDS. The solid state of the complex formulation was prepared using a spray-drying process. The spray-dried formulation of telmisartan/L-PGDS powder showed a typical spray-dried particle without any change in the secondary and tertiary structures of L-PGDS. Furthermore, the complex formulation showed a high rate and level of drug release in pH 1.2, 5.0, and 6.8 solutions in comparison with the active pharmaceutical ingredient (API) and commercial product. To validate the potential for oral administration of the telmisartan/L-PGDS complex in vivo, the pharmacokinetic and pharmacodynamic profiles were assessed in spontaneous hypertensive rats. An animal study revealed that the complex formulation led to a significant improvement of AUC and Cmax as compared with API, and the prolonged pharmacologic effect on blood pressure reduction was comparable with the commercial product. These results, taken together, demonstrate that this novel approach is feasible for the solubilized solid oral formulation and it can be applied to poorly water-soluble drugs to enhance oral bioavailability.

Reconstitution of archaeal ribonuclease P from RNA and four protein components.

Ribonuclease P (RNase P) is an endonuclease responsible for generating the 5(') end of matured tRNA molecules. A homology search of the hyperthermophilic archaeon Pyrococcus horikoshii OT3 genome database revealed that the four genes, PH1481, PH1601, PH1771, and PH1877, have a significant homology to those encoding RNase P protein subunits, hpop5, Rpp21, Rpp29, and Rpp30, of human, respectively. These genes were expressed in Escherichia coli cells, and the resulting proteins Ph1481p, Ph1601p, Ph1771p, and Ph1877p were purified to apparent homogeneity in a set of column chromatographies. The four proteins were characterized in terms of their capability to bind the cognate RNase P RNA from P. horikoshii. All four proteins exhibited the binding activity to the RNase P RNA. In vitro reconstitution of four putative RNase P proteins with the in vitro transcripted P. horikoshii RNase P RNA revealed that three proteins Ph1481p, Ph1601p, and Ph1771p, and RNase P RNA are minimal components for the RNase P activity. However, addition of the fourth protein Ph1877p strongly stimulated enzymatic activity, indicating that all four proteins and RNase P RNA are essential for optimal RNase P activity. The present data will pave the way for the elucidation of the reaction mechanism for archaeal as well as eukaryotic RNase P.