Rhabdomyolysis complicating doxylamine overdose

A 16-year-old male presenting with anticholinergic symptoms was found to have hematuria and oliguria. Evaluation of the patient revealed a serum creatinine of 2.2 mg/dl, myoglobinuria, and a creatine phosphokinase (CPK) level of 78, 750 IU/l with 99 percent fraction 3 isoenzyme. A toxic screen showed the presence of doxylamine, an antihistamine of the ethanolamine class, at a level of 75 times therapeutic. The patient did not have a history of trauma or seizures. The extremely high CPK level with the doxylamine overdose suggests that doxylamine may be associated with nontraumatic rhabdomyolysis. This is the first case report of rhabdomyolysis being associated with an antihistamine overdose.