WASHINGTON — The Food and Drug Administration on Tuesday warned consumers not to take popular heartburn medications Nexium or Prilosec if they use Plavix, a widely prescribed blood thinner that guards against heart attack and stroke.
The two heartburn formulations can reduce the protective blood-thinning effect of Plavix by nearly half, according to a study undertaken at the request of the FDA by the blood thinner's marketers, Sanofi-Aventis and Bristol-Myers Squibb.
Nexium and Prilosec inhibit a liver enzyme that is involved in converting Plavix into active form.
Plavix and Nexium were the second- and third-bestselling pharmaceuticals in the world last year, with sales of $8.6 billion and $7.8 billion, respectively, according to data research firm IMS Health. Over 11 years, 90 million people have received Plavix, according to industry records.
The FDA said it did not have enough information to say whether other drugs in the same class as Nexium and Prilosec -- known as proton pump inhibitors -- also react adversely with Plavix, said Mary Ross Southworth of the agency's center for drug evaluation and research. This includes such drugs as Prevacid and Protonix.
"There are ongoing studies to look at those other drugs," Southworth said.
Patients who need an acid-reducing medication can use traditional antacids such as Mylanta and Maalox, or most of the drugs in a class called H2 blockers that includes Pepcid, Axid and Zantac, the FDA said.
The agency offered a milder caution against using one H2 blocker, Tagamet, which has a similar enzyme-inhibiting effect on Plavix. That warning is less pointed, the agency said, because Tagamet has not specifically been studied for its interaction with the blood thinner.
Heartburn medications are commonly used with Plavix because it can cause an upset stomach.
The FDA's warning bolsters an advisory issued in January. At that time, the FDA recommended that healthcare providers "reevaluate the need for starting or continuing" use of Prilosec and other heartburn drugs but did not specifically advise against using them with Plavix.
With Tuesday's caution from the FDA, Plavix's marketers announced that they "have updated the warnings section of the Plavix label to advise that concomitant use of Plavix and drugs that inhibit [the enzyme] . . . should be avoided," a Sanofi-Aventis statement said.
A leading medical industry watchdog welcomed the FDA's action, but said it came late and was not forceful enough.
The FDA should have required a more prominent "black box" warning, said Dr. Sidney Wolfe, director of Public Citizen's Health Research Group.
"You're getting a less effective dose of a potentially life-saving drug," said Wolfe, who also is a member of the FDA's drug safety and risk management committee. "This is a serious issue."
Nexium was developed by AstraZeneca as its closely related predecessor, Prilosec, neared the expiration of its patent in 2001.
Prilosec now is marketed as an over-the-counter drug by Procter & Gamble and also is sold generically as omeprazole.