May 22, 2008— -- Hundreds of patients taking Pfizer Inc's anti-smoking drug Chantix have reported serious accidents, vision problems and heart trouble, researchers said on Wednesday, sending shares of the world's largest drugmaker to their lowest level since 1997.
U.S. aviation regulators responded quickly to the research,saying they would prohibit use of Chantix by private andcommercial pilots, while consumer advocates called for strongerwarnings on the drug's label.
Chantix, also known as varenicline, has already been linkedto depression and suicide, among other problems.
Researchers at the nonprofit Institute for Safe MedicationPractices, and Wake Forest University, said they found hundredsof reported problems since the drug's 2006 approval thatincluded blurred vision, dizziness, confusion and loss ofconsciousness.
"These data provide a strong signal that the risks ofvarenicline treatment have been underestimated and show that awide spectrum of serious injuries are being reported in largenumbers," the researchers said.
The data does not definitively prove that Chantix is atfault but does show a strong signal, the researchers cautioned,adding that the U.S. Food and Drug Administration and Pfizershould take further steps, including conducting more studies.
Pfizer officials defended Chantix, one of the strugglingdrugmaker's newest medicines, saying the side effects arealready mentioned on the drug's label.
"When you've got the nicotine withdrawal along withChantix, it's just very difficult to tell what is causing it,"said Gretchen Dieck, Pfizer's senior vice president for safetyand risk management.
Chantix works by targeting brain receptors affected bynicotine, tobacco's addictive ingredient. The drug blocks someof the effects of nicotine while also providing a nicotine-likebuzz to help curb withdrawal.
Shares of the drugmaker fell 1.2 percent to $19.76 inafter-hours trading Wednesday following release of the study,having closed on the New York Stock Exchange down 4 cents at$20.01.
Pfizer has touted Chantix as one of its biggest hopes forfuture earnings growth, but its sales have been hurt in recentmonths by safety concerns.
In February, the FDA warned about the risk of mood andbehavior changes with Chantix and called for new warnings onthe drug's label. It also said the drug could impair patients'ability to drive or use heavy equipment.
The drug brought in $277 million in U.S. sales during thefirst quarter of 2008, but has since seen its prescriptionsfall 5 percent, according to Bear Stearns analyst John Boris.On Monday he revised his estimate for 2008 sales to $640million, down from $915 million.
But Morningstar analyst Damien Conover said the new datawas not surprising, given that many smokers have multiplehealth problems.
Conover said many smokers might accept the risks for abetter chance to quit smoking, which can cause lung cancer andother health problems. He said Chantix should still bring inglobal sales this year of $1 billion.
FDA spokeswoman Susan Cruzan said the FDA was stillinvestigating the drug's psychiatric effects. Wider reviews ofnew drugs like Chantix were desirable but "FDA currently doesnot have adequate staffing to conduct such reviews."
The same brain receptors targeted by Chantix also controlmuscle movement, according to the researchers, who combed FDAdata on reported side effects.
They found 173 reports of accidents and injuries in peopletaking Chantix. They also found 397 cases of psychotic behaviorand another 227 involving suicidal behavior.
Hundreds of cases of severe skin swelling, heart problemsand diabetes were also reported.
The Federal Aviation Administration said 150 pilots and 30air traffic controllers used Chantix, but it was unclear howmany of the pilots worked for airlines.
While the FAA was not aware if any accidents linked to useof the drug, "it's prudent to deem the drug no longeracceptable for use," agency spokesman Les Dorr said.
The new study prompted the Health Research Group ofconsumer advocacy group Public Citizen to call for stronger"black box" warnings on the drug's packaging.
(Additional reporting by Ransdell Pierson in New York and JohnCrawley in Washington; Editing by Tim Dobbyn)