The ethanol extract (95%) of the root of the plant Cryptolepis buchanani (EECB) was investigated for immunomodulatory activity in mice and rats. The oral administration of EECB caused significant stimulation of the delayed type hypersensitivity (DTH) reaction and humoral antibody production. The oral LD50 was found to be more than 3 g/kg in both rats and mice.

Piperine, an alkaloid present in a number of Piper species, selectively enhances the bioavailability of structurally and therapeutically different drugs, either by increasing the absorption or by delaying the metabolism of the drug or by a combination of both processes. Dapsone, a widely used anti-leprosy drug, is known to produce methaemoglo-binaemia as a serious side effect. Based on the reported interaction of piperine with drug-metabolizing enzymes, the present investigation was undertaken to study changes in bioavailability of dapsone and possible reduction in methaemoglobinaemia in the presence of piperine in rats. A Cmax value of 2.4±0.12 μg mL−1 was obtained with dapsone alone (10 mg kg−1), compared with 3.90 ± 0.16 μg mL−1 obtained with a combination of dapsone (10 mg kg−1) and piperine (10 mg kg−1). This represents an increase of 62% in peak plasma levels caused by the presence of piperine. Reduction in total clearance from 4.80 ± 0.31 to 3.81 ± 0.20 mL h−1, and a volume of distribution from 4.61 ± 0.19 to 3.08 ± 0.12 L resulted in a net increase of 35% in AUC (34.55 ± 1.83 to 46.70 ± 3.14) in the presence of piperine. We conclude that piperine significantly (P < 0.001) enhances the bioavailability of dapsone.