The Food and Drug Administration has concluded that it can force drugmakers to switch some of their prescription drugs to over-the-counter medications as a way to make them cheaper and more easily available to consumers, senior FDA officials said yesterday.

The prospect of forced switches is strongly opposed by drugmakers, who say that the policy could result in the unsafe use of some drugs. But the momentum toward requiring drug companies to make certain products available over the counter appears to be growing, and two popular prescription allergy medications -- Allegra and Zyrtec -- will likely be the test cases if the FDA decides to go forward.

FDA Commissioner Mark B. McClellan confirmed that the issue of forced switches is being "actively considered," and that the agency has concluded it has the legal and regulatory authority to require them.

"Our first mandate is to make sure that drugs on the market are safe and effective," he said in an interview yesterday. "But we also need to be conscious of the fact that health care cost and accessibility are a primary concern to Americans, and that actions to address those issues support our health care mission."

Over-the-counter drugs are usually much cheaper than prescription drugs. But the initial benefits of moving drugs to over-the-counter status typically go to employers and insurance companies rather than consumers, because insurance usually covers only prescription drugs.

McClellan, who is both a doctor and an economist, has emphasized the need to hold down drug costs in a manner unusual for an FDA commissioner, and he has looked to the over-the-counter market as one way to make medications cheaper. The FDA's proposed budget for 2004 includes a request for the first increase in funding for its over-the-counter activities in almost 30 years, and language that asserts that more drugs that require a prescription can be sold safely on drugstore shelves.

The issue of switching drugs to over-the-counter status came up dramatically last year with the allergy drug Claritin, one of the most widely prescribed medications on the market and a very costly one for health insurers. Responding to a citizen's petition from a California health insurer to make the drug available without prescriptions, the FDA encouraged the drug's manufacturer, Schering-Plough, to make the switch. The company initially resisted, but later agreed to the change and so did not force the legal issue of whether the FDA has the authority to require a switch.

The manufacturers of the two drugs under FDA consideration for forced switches -- Pfizer Corp.'s Zyrtec and Aventis's Allegra -- say they oppose the FDA efforts, as does the organization that represents the makers of over-the-counter drugs. They also question whether the FDA has the legal authority it claims -- and the issue may be litigated if McClellan goes ahead with efforts to force over-the-counter sales.

The makers of Allegra and Zyrtec are less likely to follow the example of Schering-Plough and Claritin because their products still have many years of lucrative protection against generic copies through their patents. Most of the drugs that are sold directly to consumers overthe counter are former prescription medications for which the patents expired, and the makers of Claritin agreed to sell over the counter only because the patent was set to expire last year.

FDA officials said they have studied the issue of forcing companies to give drugs over-the-counter status since the citizen's petition in 1998, and concluded recently that the agency has the legal right to do so. They rested their conclusion, in part, on the FDA's legal authority to regulate the safety of all drugs, including whether or not they require a doctor's prescription to ensure the protection of patients.

"We believe we have the authority to determine whether or not a product is Rx or OTC," said John K. Jenkins, director for new drugs at the FDA's Center for Drugs and Evaluation. "The agency is being very careful to consider the policy implications. This is setting agency policy."

Drug company representatives said they are closely following the FDA's claims but did not indicate whether they would pursue legal action.

As part of its look at policy implications, an FDA official said the agency is putting together possible "guidance" for the drug industry to follow regarding over-the-counter switches in case it decides to go that direction.

Claritin, Allegra and Zyrtec are sold without a doctor's prescription in many other countries, and in some cases have been sold that way for many years. An FDA advisory panel of specialists concluded in 2001 that the class of drugs could be safely sold directly to consumers here and recommended that the FDA work toward that end.

The FDA had one prior experience with a forced switch to over-the-counter sales, and it was quickly rescinded. The makers of the antihistamine metaproterenol, or Alupen, were tentatively required to sell their drug without a prescription in 1982. But after opposition from doctors and some negative reactions from patients, the company pulled the drug from the shelves and the FDA rescinded its order.

The Consumer Healthcare Products Association (CHPA), which represents the makers of over-the-counter drugs, referred to that experience in a letter last month to the FDA and Health and Human Services Secretary Tommy G. Thompson that opposed forced switches. "We understand that the FDA is considering a switch of a second generation antihistamine, from prescription to OTC status, over the objections of the company," wrote CHPA President Linda A. Suydam.

"Attempting to force a switch would be a misallocation of FDA's very limited and finite resources available for OTC activities," she wrote. "By diverting OTC resources to try to force a switch where the sponsor is opposed, FDA loses the opportunity to make important gains in OTC" regulation. She also wrote that the FDA has a "significant backlog of switch applications" from sponsors who want to move their products to over-the-counter status.

According to McClellan, the price of Claritin has dropped from $3 a pill as a prescription drug to less than $1 a pill since going to over-the-counter sales early this year.

The chief beneficiaries so far have been insurance and drug benefit companies, which no longer have to cover Claritin costs and often have dropped Allegra and Zyrtec coverage as well. A monthly supply of over-the-counter Claritin now costs more than the co-pay that many insured patients were charged when it was a prescription drug. But McClellan said the elderly and some uninsured are already paying less for Claritin and everyone will in time as more generic versions of the drug come on the market.

The FDA's action is something of a response to the steep decline in the number of drugs switching to over-the-counter status in recent years. According to the newsletter Switch, compiled by the over-the-counter consulting firm Francesco International, there were 21 significant and advertisable drugs switched to over-the-counter status in the major drug-manufacturing nations in 1995, but only three in 2002.