CYCLOSPORINE-AMIODARONE INTERACTION

OBJECTIVE: To report a possible interaction between cyclosporine (CsA) and amiodarone in a kidney transplant recipient. CASE SUMMARY: A 66-y ear-old kidney transplant recipient with a history significant for hyp ertension, moderate mitral valve insufficiency, and decreased left ven tricular function developed ventricular tachycardia ventricular and wa s eventually treated with amiodarone. Maintenance immunosuppression in cluded prednisone, azathioprine, and CsA. CsA concentrations before am iodarone initiation were stable (range 100-150 ng/mL). After amiodaron e initiation, the CsA concentration increased more than twofold. Follo wing CsA dosage reduction, concentrations returned to the desired rang e. The patient did not experience any toxicity with the increased conc entration of CsA. DISCUSSION: The possible mechanisms of an interactio n between CsA and amiodarone are reviewed. Reports of this interaction in heart transplant recipients are also reviewed. Changes in protein binding, changes in metabolism, or both may explain the interaction. B oth CsA and amiodarone are protein bound and metabolized by the cytoch rome P-450 enzyme system. CONCLUSIONS: It is likely that there is an i nteraction between CsA and amiodarone. The exact mechanism of this int eraction has not been fully determined. When CsA is administered concu rrently with amiodarone, CsA concentrations should be monitored closel y and the CsA dosage should be adjusted as necessary.