Objective: To describe a potential drug interaction between amiodarone and clonazepam.
Case summary: A 78-year-old man with a history of congestive heart failure and coronary artery disease began taking amiodarone to suppress sustained ventricular tachycardia. Following the development of restless leg syndrome, therapy with clonazepam 0.5 mg qhs was initiated. Subsequently, the patient demonstrated signs and symptoms of benzodiazepine toxicity, which cleared following the discontinuation of clonazepam.
Discussion: Amiodarone is a Class III antiarrhythmic with an adverse-effect profile involving many different organ systems. It also has been shown to inhibit the metabolism of drugs cleared by oxidative microsomal enzymes. Clonazepam undergoes extensive hepatic metabolism, primarily by reduction and acetylation, and is therefore susceptible to altered disposition during concomitant administration of agents that inhibit hepatic microsomal enzymes. Hypothyroidism, occurring in up to 11 percent of patients treated with amiodarone, can also alter drug metabolism and sensitize the central nervous system, thus increasing the potential for toxicity. It is likely that a combination of these factors was responsible for the symptoms described in this patient.
Conclusions: The complex pharmacologic profile of amiodarone and its effects on multiple organ systems necessitates close patient monitoring during concurrent administration of medications such as clonazepam, which are cleared by oxidative metabolism.