ABSTRACT
The stability of rifampicin in the presence of isoniazid was studied using several in vitro examinations including differential scanning calorimetry, infrared spectroscopy and thin layer chromatography. The results suggested the probability of the interaction between rifampicin and isoniazid. Regarding in vivo studies, the effect of isoniazid 5 mg kg-1 on the pharmacokinetics of rifampicin 10 mg kg-1 was investigated in dogs after single oral administration. Plasma rifampicin concentrations were determined using high performance liquid chromatographic assay for the determination of the drug. The effect of repeated oral administration of rifampicin-isoniazid [R-I] combination, for a period of five days in dogs, on hepatic enzymatic activity and renal function tests was studied. The present study showed a good agreement between both in vitro and in vivo results. In addition, the pharmacokinetic of rifampicin was found to be influenced by the presence of isoniazid