Impact of traditional medicinal plant extracts on antiretroviral drug absorption

Ethopharmacological relevance: Traditional herbal medicines are often used for the treatment of different diseases in developing countries, especially in the rural areas where a lack of an efficient primary health care system is usually experienced. Many patients infected with the human immunodeficiency virus are taking traditional herbal medicines in conjunction with their modern antiretroviral medication and drug-herb interactions can occur in these cases. Aim of the study: To investigate the effect of water extracts of two traditional medicinal plants, Hypoxis hemerocallidea and Sutherlandia frutescens as well as L-canavanine (a constituent of Sutherlandia frutescens) on the transport of nevirapine across human intestinal epithelial cells. Materials and methods: Nevirapine transport in the apical to basolateral and basolateral to apical directions across Caco-2 cell monolayers was determined alone (normal control) and in the presence of verapamil (positive control), water extracts of Hypoxis hemerocallidea and Sutherlandia frutescens and an aqueous solution of L-Canavanine. The cumulative transport and apparent permeability coefficient (P-app) values were calculated and compared. Results: Nevirapine alone was substantially effluxed in the basolateral to apical direction across the intestinal epithelial cell monolayers, which was statistically significantly (p <= 0.05) decreased by addition of verapamil, Hypoxis hemerocallidea extract and the L-canavinine solution. The effect of Sutherlandia frutescens on nevirapine transport was not statistically significantly different from the control. Conclusions: Hypoxis hemerocallidea and L-canavanine interact with the efflux of nevirapine across intestinal epithelial cells and therefore can potentially increase the bioavailability of this antiretroviral drug when taken concomitantly. (C) 2008 Elsevier Ireland Ltd. All rights reserved.