Drug interactions occurring during absorption from the gastrointestinal tract

Eudragit®-based microcapsules of probucol with a gut-bacterial processed secondary bile acid

AIM

Deoxycholic acid (DCA) has improved gliclazide oral absorption, while Eudragit^® (ED) polymers have improved formulation stability of antidiabetic drugs. The aim of the study is to test if DCA and ED encapsulation will optimize the release and stability of the potential antidiabetic drug probucol (PB).

MATERIALS & METHODS

The PB formulations were prepared using ED polymers and DCA, and formulations were analyzed for their rheological and biological properties.

RESULTS

Rheological properties and size distribution were similar among all groups. β-cell survival and biological activities were best with NM30D microcapsules. The inflammatory profile and oxidative stress effects of microcapsules remained similar among all groups.

CONCLUSION

ED NM30D and DCA incorporation can exert positive and stabilizing effects on PB oral microcapsules.

Reduced Food-Effect on Intestinal Absorption of Dronedarone by Self-microemulsifying Drug Delivery System (SMEDDS)

The oral absorption of dronedarone (DRN), a benzofuran derivative with anti-arrhythmic activity, is significantly affected by food intake. The absolute bioavailability of the marketed product (Multaq, Sanofi, U.S.) was about 4% without food, but increased to 15% when administered with a high fat meal. Therefore, to reduce the food-effect on the intestinal absorption of DRN, a novel self-microemulsifying drug delivery system (SMEDDS) was formulated and the comparative in vivo absorption studies with the marketed product were carried out using male beagle dogs either in the fasted or fed state. The SMEDDS consisted of the drug, Labrafil M 1944CS, and Kolliphor EL in a weight ratio of 1 : 1 : 2, rapidly formed a fine oil-in-water emulsion with a droplet size less than 50 nm. An in vivo absorption study revealed that the area-under-curve (AUC0-24 h) and maximal plasma concentration (Cmax) were 10.4-fold (p<0.05) and 8.6-fold (p<0.05) higher, respectively, after the marketed product was orally administered to beagles in the fed state when compared to those in the fasted state. This food-effect were remarkably alleviated by SMEDDS formulation, with AUC0-24 h and Cmax 2.9-fold (p<0.05) and 2.6-fold (p<0.05) higher in the fed state when compared to the fasted state, by facilitating intestinal absorption of DRN in the fasted state. The results of this study suggest that SMEDDS may decrease the differences in oral absorption of DRN between the prandial states, improving therapeutic efficacy as well as patient compliance.

Physiochemical and physiological mechanisms for the effects of food on drug absorption: the role of lipids and pH

Drugs are absorbed after oral administration as a consequence of a complex array of interactions between the drug, its formulation, and the gastrointestinal (GI) tract. The presence of food within the GI tract impacts significantly on transit profiles, pH, and its solubilization capacity. Consequently, food would be expected to affect the absorption of co-administered drugs when their physicochemical properties are sensitive to these changes. The physicochemical basis by which ingested food/lipids induce changes in the GI tract and influence drug absorption are reviewed. The process of lipid digestion is briefly reviewed and considered in the context of the absorption of poorly water-soluble drugs. The effect of food on GI pH is reviewed in terms of location (stomach, upper and lower small intestine) and the temporal relationship between pH and drug absorption. Case studies are presented in which postprandial changes in bioavailability are rationalized in terms of the sensitivity of the physicochemical properties of the administered drug to the altered GI environment.

Estimation of the increase in solubility of drugs as a function of bile salt concentration

PURPOSE

The objective of this study was to develop a model to predict the extent to which bile salts can enhance the solubility of a drug, based on the physicochemical properties of the compound. The ability to predict bile salt solubilization of poorly soluble drugs would be a key component in determining which drugs will exhibit fed vs. fasted differences in drug absorption.

METHODS

A correlation between the logarithm of the octanol/water partition coefficient [log P] of six steroidal compounds and their solubilities in the presence of various concentrations of sodium taurocholate at 37 degrees C, log [SR] = 2.234 + 0.606 log [P] (r2 = 0.987) where SR is the ratio of the stabilization capacity of the bile salt to the solubilization capacity of water for the drug, was used to predict the solubility of the compounds in presence of sodium taurocholate were then measured.

RESULTS

The predicted solubilities were within 10% of the experimentally observed solubilities for griseofulvin, cyclosporin A and pentazocine. The model overpredicted the solubility of phenytoin and diazepam in 15 mM sodium taurocholate solution by a factor of 1.33 and 1.62 respectively.

CONCLUSIONS

The expected increase in solubility as a function of bile salt concentration can be estimated on the basis of the partition coefficient and aqueous solubility of the compound.

Toxicological consequences of multiple chemical interactions: a primer

The capacity to understand and successfully predict the toxicological consequences of multiple chemical interactions is a critical challenge facing the scientific community. This article is designed to provide a broad framework introducing the concept of interaction, use of consistent and meaningful terminology and a descriptive assessment of toxicological foundations within which chemical interactions may be evaluated. The article offers guidance on the need to place a high priority on assessing the mechanistic basis of 'superinteractions', that is, unique interactions far exceeding even those of a multiplicative nature. The final section of the article provides a detailed perspective on how the extensive and successful experience of the pharmaceutical industry in assessing and interpreting any interaction for patients can be useful to the issues and concerns of chemical interactions for the field of environmental toxicology and risk assessment.

Oxprenolol absorption in man after single bolus dosing into two segments of the colon compared with that after oral dosing

The systemic availability of oxprenolol after colonic and oral administration has been compared in a crossover study involving six healthy male volunteers. Drug administration into two regions of the colon (caecum and left flexure) was achieved by means of a colonoscopic technique. There were no obvious differences in plasma concentrations after drug administration to the caecum and left flexure, although in one subject it was necessary to repeat colonic administration because of unexpectedly high plasma drug levels on the first occasion. The possible reasons for this abnormal response are discussed. The mean systemic availability of oxprenolol was 82% after colonic compared with oral dosing, although marked differences were observed in individual plasma levels following drug administration by the two routes. The results of this study support the concept of extending the duration of oxprenolol release from a rate-controlled dosage form to permit once-daily administration with this short elimination half-life drug.