A patient chronically takes tizanidine for back pain. He presents to the Emergency Department with sedation, bradycardia and hypotension after taking a first dose of a new antibiotic? What drug was he started on?
Granfors MT et al. demonstrated that, in healthy volunteers given ciprofloxacin and tizanidine, ciprofloxacin significantly elevated the peak plasma concentration of tizanidine by 7-fold. This drug-drug interaction is due to ciprofloxacin's ability to inhibit CYP 1A-2. (Granfors MT et al. Ciprofloxacin greatly increases concentrations and hypotensive effect of tizanidine by inhibiting its cytochrome P450 1A2- mediated presystemic metabolism. CPT 2004; 76(6):598-606.)