Pfizer’s Zyvox and Antidepressants May Be Fatal Combination

Pfizer Inc. (PFE)’s Zyvox antibiotic can cause potentially fatal central nervous system reactions in patients who also take antidepressants that increase levels of the brain chemical serotonin, U.S. regulators said.

Pfizer’s Zoloft and Pristiq, Eli Lilly & Co. (LLY)’s Cymbalta and GlaxoSmithKline Plc (GSK)’s Paxil and Wellbutrin are among 29 psychiatric drugs that patients may need to stop taking temporarily when they require treatment with Zyvox, the Food and Drug Administration said today in a drug safety communication.

Zyvox, used to treat some types of drug-resistant bacteria including MSRA or methicillin-related Staphylococcus aureus, skin infections and nosocomial pneumonia, can interact with the antidepressants to cause a toxic reaction known as serotonin syndrome in which excess amounts of the chemical build up in the brain, according to the FDA.

Some deaths among patients who suffered such a reaction were reported to the FDA’s adverse-event database, the agency said. Pfizer, based in New York, reported $1.18 billion in revenue from Zyvox last year.

Excess Serotonin

Confusion, memory issues, hyperactivity, excessive sweating and muscle twitching are among the symptoms of excess serotonin levels. Patients taking psychiatric drugs shouldn’t stop using them without first consulting a health-care professional, the FDA said.

The current U.S. package insert for Zyvox “already includes prominent information regarding the potential for serotonergic interactions, the risk of serotonin syndrome and the need for careful observation of patients prescribed Zyvox who are on such agents,” Kristen Neese, a Pfizer spokeswoman, said today in an e-mail. The company hasn’t identified any new safety signals related to those drug interactions, she said.

“In an ongoing commitment to ensure patient safety, Pfizer continually monitors all relevant safety information including information pertaining to the concomitant use of Zyvox and serotonergic antidepressant medications,” Neese said.

To contact the reporter on this story: Molly Peterson in Washington at mpeterson9@bloomberg.net

To contact the editor responsible for this story: Adriel Bettelheim at abettelheim@bloomberg.net

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