The compound phenylephrine, marketed by Pfizer Inc. as Sudafed PE, isn't sufficiently absorbed into the bloodstream to make it an effective oral medication, according to Leslie Hendeles and Randy C. Hatton, pharmacists at the University of Florida.
The researchers recently raised the issue in a pharmaceutical journal because they are concerned that people will buy a medication that doesn't work -- not realizing that a better drug is available a few feet away -- if they ask for it.
A Pfizer spokesman said the new drug is effective and that consumers can ask for the original Sudafed if they want it.
The problem arose this year after the Food and Drug Administration acted on complaints that criminals were buying bulk quantities of Sudafed tablets and generic look-alikes for their key ingredient, a compound known as pseudoephedrine.
Police say that criminals are turning pseudoephedrine into highly potent (and illegal) methamphetamine.
Although pseudoephedrine -- a long-used, effective decongestant -- is still available without prescription, the FDA has ordered pharmacies to pull Sudafed and similar tablets from open shelves by Sept. 30 and keep them behind the counter. The government also wants pharmacies to ask for identification from customers buying Sudafed, maintain a log of buyers and limit daily purchases.
For open shelf display, Pfizer replaced Sudafed with the similarly named Sudafed PE, whose active ingredient is a different chemical -- phenylephrine.
Hendeles said that phenylephrine is considered effective when doctors give it intravenously to regulate blood pressure in surgical patients, and when consumers use it in nasal sprays to fight cold symptoms. (Nasal sprays aren't recommended for allergies because if they are used for more than a few days, they can have a "rebound effect" and make congestion worse, experts say.) But the researchers noted that the FDA approved phenylephrine in relatively low, 10-milligram oral doses in 1976, averting the need for clinical trials.
They said studies conducted since then consistently have shown that when phenylephrine is taken orally, enzymes in the gut or liver prevent it from being absorbed in the bloodstream. As a result, in 10-milligram doses, only 38 percent of the drug is absorbed into the bloodstream, compared with a 90 percent absorption rate for the active ingredient in Sudafed, the researchers say.
Phenylephrine might be effective in higher oral doses, Hendeles said - but drug companies should conduct clinical trials to see whether those doses are safe and effective.
Hendeles and Hatton expressed their concerns in a letter to the editor of the Journal of Allergy and Clinical Immunology.
Other critics say that Sudafed PE and other oral phenylephrine decongestants have been put on the market because drug companies are worried about losing profits if their products disappear from store shelves.
"They're trying to protect their market share," said Dr. Miles Weinberger, director of pediatric allergy and pulmonary care at the University of Iowa College of Medicine in Iowa City.
Pfizer disputed the researchers' conclusions about phenylephrine. "People are telling us they're getting relief from it," said Erica Johnson, a Pfizer spokeswoman.
Sudafed PE has been on the market since February 2005 and sales figures and consumer tests show that it's working, she said.
She declined to release sales figures. But she pointed out that Sudafed remains an option for customers concerned about the effectiveness of Sudafed PE.
"All they have to do is ask for it," she said.
Distributed by the Los Angeles Times-Washington Post News Service