Psychotic episode induced by potential drug interaction of sibutramine and finasteride

Abstract

A case of drug interaction is here described in a 30-year patient undergoing a successful anti-obesity treatment with sibutramine. Sibutramine is a drug that inhibits serotonine and noradrenaline reuptake. Soon after the introduction of finasteride to treat his alopecia, a paranoid-psychotic behavior developed. Finasteride is a powerful 5-alpha-reductase type 2 inhibitor. Drug interaction is shown through a careful clinical follow-up and the application of Naranjo algorithm. The patient's general condition and clinical progression are also described. In addition, the most likely mechanisms of drug interaction are discussed. It seems that finasteride inhibited the hepatic metabolism of sibutramine that, by its turn, displaced finasteride from its plasma protein binding. This phenomenon resulted in higher plasma levels of finasteride and lower metabolism of sibutramine, which probably increased the levels of serotonine, noradrenaline and dopamine in the synaptic gap, triggering the psychotic manifestation.