Subcellular changes of rat myocardium after treatment with amiodarone or desethylamiodarone, studied with electron microscopy.

Amiodarone, an antiarrhythmic agent, has proven to be unique in its capability to control arrhythmias unresponsive to conventional drugs. However, its association with many undesirable side effects after chronic usage has become just as clear. Chronic clinical toxicity with amiodarone is associated with intracellular lamellar or myelinoid inclusion bodies (onionoid bodies or corpora cepiformia) in various organs (i.e. skin, cornea, lung, liver, and lymph nodes). Previous study has demonstrated formation of these inclusion bodies in canine myocardium following multiple doses of amiodarone. The present study was designed to develop a more convenient animal model, and to measure the concentration of amiodarone, as well as desethylamiodarone (its major metabolite) in this rodent model. The direct role of desethylamiodarone in formation of lamellar inclusion bodies in rat myocardium was also investigated. Amiodarone (50 mg/kg) or desethylamiodarone (25 mg/kg) was injected intraperitoneally daily for a period of 14 days. Myocardial sections revealed the presence of lamellar inclusion bodies, round or oval in appearance, in the form of laminated or concentrically arranged membranes after either amiodarone or desethylamiodarone treatment. This is the first reference to the induction of these myelinoid inclusion bodies with desethylamiodarone. Myocardial tissue concentrations of amiodarone and desethylamiodarone exceeding plasma concentrations were found in the present study and indicate the capability of these compounds to easily distribute and accumulate in the myocardium.