[Thrombopenia due to pefloxacin (Peflacine): dose-dependent toxicity?]

Pefloxacin (Peflacine) can give rise to thrombocytopenia, although the responsibility of the drug can be difficult to demonstrate in infectious patients and those receiving other drugs simultaneously. We have collated 18 cases in which the responsibility of pefloxacin was suspected. In 13 cases, the patients were also taking other drugs which may have been contributory (heparin, Bactrim, Augmentin, ranitidine,...). The remaining five cases were of particular interest as pefloxacin was the only drug administered. The mean age of the patients was 75 years, and the mean bodyweight 56 kg (range, 47-65 kg). The pefloxacin dosage was 800 to 1,600 mg/day i.v. or p.o., i.e. 13-18 mg/kg/day. Thrombocytopenia occurred from five to 19 days after beginning treatment and resolved between 7 and 12 days after drug withdrawal. A number of factors argue in favor of dose dependency: 1 patient had high plasma concentrations (peak and residual); thrombocytopenia occurred in one patient when the previous, well-tolerated dosage of 800 mg/day (for 15 days) was increased to 1,600 mg/day; thrombocytopenia resolved in one patient when the dosage was reduced to 400 mg/day (1 tablet) and continued for a further 10 days. This toxic reaction may be avoided by reducing the drug dosage to 400 mg/day in elderly patients with a low bodyweight. Differential blood counts appear to be warranted for patients at risk.