Sudden-Onset Dystonia in a Patient Taking Asenapine: Interaction Between Ciprofloxacin and Asenapine Metabolism

This report highlights a potential drug-drug interaction between asenapine and ciprofloxacin that has not been previously reported. Ciprofloxacin is a potent inhibitor of CYP1A2 but not of UGT1A4 (1); interactions between it and second-generation antipsychotics that are metabolized through the CYP1A2 pathway have been reported. According to a published case report, coadministration of ciprofloxacin and olanzapine increases olanzapine serum levels (3). Ciprofloxacin pharmacokinetics (a half-life of 4 hours and steady state after 3 days [1]) demonstrate that it was the identifiable precipitant of this patient’s dystonia. Other possible contributing factors include the effect of inflammation and infection, including urinary tract infections, on down-regulation of CYP1A2 (4) as well as potential inhibition of asenapine glucuronidation by valproate (5). These factors may have exacerbated the patient’s symptoms, although the dystonia was not noted until after initiation of ciprofloxacin. Utilization of a rating scale to assess the likelihood of drug-drug interaction indicated that this inference is “probable” (6).

This case may serve as a reminder that we must be mindful of drug-drug interactions when prescribing second-generation antipsychotics.