The Tufts study, published in the Jan. 1 edition of the British Medical Journal, added that "insured patients faced with high co-payments on their prescriptions may also benefit financially from over-the-counter availability."

Switching drugs from Rx to OTC status "is an evolution," Joshua P. Cohen, senior research fellow for the Tufts Center for the Study of Drug Development, said in an interview. "It's based on a combination of clinical factors, consumer responsibility and the changing role of the FDA."

Cohen expects another flurry of Rx-to-OTC switches in the next few years amid an environment of rising drug costs, insurance company pressure and patent expirations on big-selling drugs. "It is, for the most part, cost-driven," he said.

Since the mid-1970s, changing physician, regulator and patient attitudes have affected the marketing of antihistamines, pain relievers, heartburn remedies, hair-loss treatments and smoking-cessation drugs. Some of the most famous prescription names of yesteryear -- Claritin, Rogaine, Pepcid, Zantac, Nicorette, Prilosec -- are all now sold without a prescription.

Is Mevacor next? Four years ago, Merck asked the FDA to make it a nonprescription drug, but FDA advisory committees said Merck failed to prove the drug could be used safely by consumers without a prescription. The FDA also rejected an attempt by Bristol-Myers Squibb ( BMY) to get the cholesterol drug Pravachol approved for OTC use. Bristol-Myers Squibb recently submitted another request for OTC Pravachol, but only Mevacor is scheduled for an FDA advisory committees' review on Jan. 13 and 14.

Saving Money

When companies switch drugs, consumer savings often depend on whether the out-of-pocket cost for an OTC drug is lower than the co-payment someone makes to his insurer for an Rx drug.

"There is a lot more to consider than just the cost of prescription co-payments, which vary greatly," says the Consumer Products Healthcare Association. "Other circumstances must be factored in, such as the fee for the doctor's visit, travel costs and time off from work."

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