FDA withdraws channel blocker
Taper, wait 1-2 weeks before starting new meds
On June 8, the Food and Drug Administration (FDA) pulled Roche's calcium channel blocker Posicor (mibefradil) on grounds that it is dangerous, possibly lethal, in combination with other drugs. On the market less than a year, the hypertension and angina drug was known to interact with certain other medications, but when the list grew to 26 - including antihistamines, antibiotics, cholesterol-lowering meds, and tamoxifen - it was withdrawn.
Ten days later, a new warning was issued regarding Posicor. Four patients who stopped taking the drug and began taking others went into shock within 12 hours, and one died. Roche now cautions doctors to wait seven days after stopping Posicor before substituting certain dihydropyridine calcium channel blockers and two weeks before starting timolol, a beta blocker, or felodipine, a dihydropyridine calcium channel blocker. Patients need to be tapered off the drug because it remains in the bloodstream for several days.
The problems occur when Posicor is blocking some T and L channels, and a second drug is added that blocks even more L channels. When this happens in a person who is also taking beta blockers, blood pressure and heart rate can plummet to life-threatening levels.
Some critics see this incident as evidence that the FDA is relaxing its standards. Posicor passed the agency's approval panel by a slim margin, five to three, in July 1997. Since the drug's release, the agency has received dozens of reports of adverse side effects including low heart rate and irregular heartbeat in patients taking it in combination with other drugs. Patients should not stop taking the drug, but rather should consult with their physicians immediately to find an alternative. A 24-hour hotline is in place for questions: (800) 205-4611.
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