Potentiation of isoniazid-induced liver toxicity by rifampicin in a combinational therapy of antitubercular drugs (rifampicin, isoniazid and pyrazinamide) in Wistar rats: A toxicity profile study.

AIM: Biochemical characterization of long-term toxic manifestations of anti-tubercular (anti-TB) drugs - rifampicin (RIF), isoniazid (INH) and pyrazinamide (PZA) - individually and in two combinations: (i) RIF + INH, and (ii) RIF + INH + PZA in Wistar rats.

METHODS

Animals received anti-TB drugs - alone or in combination - once daily p.o. for up to 90 days (doses, in mg/kg: RIF, 250; INH, 50; PZA, 100). Assays for alanine aminotransferase (ALT), alkaline phosphatase (ALP), bilirubin (serum) and lipid peroxidation (LPO), glutathione (GSH), glutathione peroxidase (GPx), catalase, Na+K+-ATPase and CYP 2E1 (liver) were performed to assess liver toxicity. Clinical biochemistry was done by commercial kits. Determinations were made at 0, 15, 30 and 90 days of treatment schedule.

RESULTS

Anti-TB drugs-treated animals showed abnormal rises or falls (>1.5-2 fold) in the serum/liver parameters. Mild hyperlipidemia, hypercholesterolemia and hyperuricemia were the other pathologies. Of all the treated groups, INHalone or in combination with other drugs produced a progressive enhancement of toxicity over 15-90 days. The in vivo results were further supported by in vitro results (MTT assay, GSH and LPO) in primary cultures of rat hepatocyte. RESULTS indicated that anti-TB drugs in combination: (i) caused membrane damage resulting in leakage of ALT, ALP and bilirubin; (ii) caused imbalance in endogenous enzymatic oxidant-antioxidant defense via increased lipid peroxidation and in glutathione homeostasis; and (iii) enhanced the CYP 2E1-mediated bioactivation mechanism.

CONCLUSION

Toxicity manifestations seemed to be heptocytic injury targeted at hepatocytes, bile ducts or sinusoidal cells related to hepatitis and primary biliary cholestasis.