Drug interaction between carbapenems and extended-release divalproex sodium in a patient with schizoaffective disorder

Abstract

BackgroundClinicians prescribing divalproex sodium (DVX) are well aware of its potential to cause a drug-drug interaction. One specific interaction occurs between the carbapenem antibiotics and DVX resulting in decreased valproic acid (VPA) levels immediately following the initiation of this antibiotic class. Objective/MethodWe describe a case of a 46 year-old Caucasian male who had an undetectable VPA level following treatment with carbapenems. ResultsOn admission the patient's VPA level was 115 μg/ml; however, a routine VPA level on day 19 of his hospitalization returned a value of 16 μg/ml. At this point, he had received a total of 15 days of carbapenem antibiotics for treatment of lower leg cellulitis. His DVX dose was increased to a maximum of 6g daily, twice his home dose, but it did not produce a therapeutic VPA concentration. The patient was lost to follow-up before an outpatient VPA level was drawn. ConclusionOur case report is the first to document this drug-drug interaction in a patient diagnosed with schizoaffective disorder, bipolar type.