The FDA is advising physicians about 2 new warnings in the labeling of mibefradil dihydrochloride (Posicor), a calcium channel blocker. One warning uses information from new reports to strengthen language in the labeling about the association between use of mibefradil and slowing or complete suppression of sinoatrial node activity. The supervening junctional rhythms have often been as slow as 30 to 40 beats per minute. Many of the reports have incorrectly identified the adverse event as complete AV block. The reports most commonly involved elderly patients, mainly in association with the concomitant use of β-blockers. Care should be taken when combining mibefradil with β-blockers. In patients with low heart rates, use of any combination of agents that can slow the sinus node or affect the AV node (eg, β-blockers, digitalis, and the calcium channel blockers mibefradil, diltiazem hydrochloride, and verapamil) should in general be undertaken only after careful consideration, as such combinations can unmask underlying sick sinus syndrome. Use of mibefradil in patients with sick sinus syndrome without a pacemaker is contraindicated.
Nightingale SL. Two New Warnings Added to Labeling for Mibefradil. JAMA. 1998;279(5):346. doi:10.1001/jama.279.5.346