Secondary thrombocytopenia following phenobarbital treatments in a rhesus monkey (Macaca mulatta)

A rare adverse reaction due to phenobarbital (10 mg/kg/day for 11 days) developed in a rhesus monkey (Macaca mulatta). Clinical signs and measured hematological parameters correlated closely with descriptions of thrombocytopenia. Following cessation of phenobarbital, the monkey recovered within 11 days. Five months after initial thrombocytopenia, the monkey was challenged again with phenobarbital (10 mg/kg/day for 11 days). Appearance and progression of clinical signs were identical to the initial crisis.