Abstracts

Rationale: Here we present a case of a previously unreported toxic interaction between pregabalin and phenobarbital. An 18-year-old girl with a 16-year history of focal seizures was being treated with levetiracetam 1000 mg bid, zonisamide 300 mg bid, phenobarbital 60 mg bid, and a vagal nerve stimulator. Her development was normal with good progression through school and involvement in numerous extracurricular activities. Despite her extensive treatment regimen, she continued to have focal seizure activity, which consisted mainly of left facial twitching and left arm jerking occurring 3 to 4 times per week lasting up to thirty minutes at a time. In an effort to provide better seizure control, she was given a trial of pregabalin 100 mg three times daily as an adjunct to her antiepileptic drug regimen.Methods: History, physical exam, laboratory evaluation, and medical record review were performed following the addition of pregabalin to this patient’s drug regimen.Results: The week following the addition of pregabalin, this very pleasant girl became progressively more irritable and moody. This culminated in the patient having “rage attacks” during which she was very combative and would not follow commands. She also had increased frequency of seizure activity consisting mainly of left sided facial twitching. On laboratory examination her phenobarbital level was 103 mcg/ml without a change in the levels of her other anticonvulsants. She required inpatient care and sedation with benzodiazepines. The phenobarbital and pregabalin were discontinued on hospital admission and the patient was maintained on her other anticonvulsant medications. Over the course of her three day hospital stay, her phenobarbital level decreased to 54 mcg/ml, and the clinical manifestations of agitation subsided. Two weeks after cessation of the pregabalin and phenobarbital, the patient was restarted on phenobarbital with drug levels within the therapeutic range. She experienced no further symptoms of phenobarbital toxicity and remained at her baseline level of functioning.Conclusions: Although pregabalin has been reported to have minimal drug interactions, this case demonstrates marked phenobarbital toxicity following addition of pregabalin to an antiepileptic drug regimen in refractory epilepsy.