Tizanidine + Rifampicin - Drug Interactions

Rifampicin moderately decreases plasma concentrations oftizanidine

Clinical evidence,mechanism, importance and management

In a placebo-controlled, crossover study in 10 healthy subjects, pre-treatment with rifampicin 600mg daily for 5 days moderately reduced AUC and peak level of a single 4mg dose of tizanidine given on day 6 by about 50%, without altering half-life (See reference number 1).

Rifampicin appears to be only a weak inducer of cytochrome P450 isoenzyme CYP1A2, by which tizanidine is metabolised (See reference number 1).

Rifampicin moderately reduces levels and effects of tizanidine. Because tizanidine dose is titrated to effect,this is probably not that clinically important. A small increase in dose might be required.

1. Backman JT,Granfors MT, Neuvonen PJ. Rifampicin is only a weak inducer of CYP1A2-mediated presystemic and systemic metabolism: studies with tizanidine and caffeine. Eur J Clin Pharmacol (2006) 62, 451–61.