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Tizanidine contraindicated for use with Luvox, Cipro.

The antispasticity drug tizanidine should not be used with fluvoxamine, ciprofloxacin, or other CYP1A2 inhibitors because of potentially dangerous interactions, according to a letter issued by the drug's manufacturer.

Concomitant use of tizanidine with the antidepressant fluvoxamine or the antibiotic ciprofloxacin is now contraindicated. (Fluvoxamine is available in generic formulations and as a trade formulation as Luvox. Ciprofloxacin, a fluoroquinolone marketed as Cipro, is also available in generic formulations.) Tizanidine, marketed as Zanaflex by Acorda Therapeutics, is a centrally acting [[alpha].sub.2]-adrenergic agonist, a short-acting drug that is indicated for management of spasticity.

The bases of these contraindications are the results of pharmacokinetic studies in which tizanidine was coadministered with either fluvoxamine or ciprofloxacin, both potent inhibitors of CYP1A2. In the studies, serum tizanidine concentration significantly increased, and the drug's hypotensive and sedative effects were potentiated.

There are no clinical studies evaluating the effects of other CYP1A2 inhibitors on tizanidine, but other CYP1A2 inhibitors "may lead to substantial increases in tizanidine blood concentrations," the company said in a "Dear health care professional" letter. "Therefore, concomitant use of tizanidine with other CYPA12 inhibitors, such as zileuton, other fluoroquinolones, antiarrhythmics (amiodarone, mexiletine, propafenone, and verapamil), cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine should be ordinarily avoided," the letter said. "If their use is clinically necessary, they should be used with caution," the letter adds.

These changes, which were added to the contraindications and warnings section of the tizanidine label, were approved by the Food and Drug Administration in July 2006, at which time, the agency asked the company to issue the letter to communicate the information to health care professionals.

Tizanidine, which was approved by the FDA in 1996, is also available in generic formulations. The company's letter also pointed out that Zanaflex capsules and tablets are not bioequivalent taken after eating. That information was already included in the drug's label, which states that prescribers should be "thoroughly familiar with the complex effects of food on tizanidine pharmacokinetics."

A link to the FDA alert and the company's letter is available at www.fda.gov/medwatch/safety/2007/safety07.htm#Zanaflex. Serious adverse reactions can be reported to Acorda at 800-367-5109 or by e-mail at Acorda@medcomsol.com, or to the FDA's MedWatch program at 800-332-1088 or www.fda.gov/medwatch.

BY ELIZABETH MECHCATIE

Senior Writer
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Title Annotation:Neurology
Author:Mechcatie, Elizabeth
Publication:Internal Medicine News
Geographic Code:1USA
Date:Aug 1, 2007
Words:385
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