Federal health regulators are requiring more than a dozen drugmakers to develop plans to reduce the misuse of their painkillers, which cause hundreds of deaths each year.

The Food and Drug Administration said Monday it has issued letters to companies that make 24 opioid drugs, including morphine, oxycodone and methadone. Opioids are drugs that simulate the effects of natural opiates, such as opium poppy.

The products targeted by FDA, which come in both pill and patch forms, generally feature extended-release formulas designed to give long-lasting effects. But regulators warned that potency carries serious risks.

"We're focusing on these products because they generally contain very high doses of the drugs and need to be used very carefully," said Dr. John Jenkins, FDA's chief of new drugs.

The drugs are typically used by people already taking narcotics, such as cancer patients, to treat severe flare-ups of pain. Despite their ability to relieve chronic pain the drugs can be highly addictive and are often abused for their euphoric effects.

The FDA has issued a number of warnings on prescription pain relievers in recent years and some companies already have plans to manage the drugs' risks.

"Despite these efforts, the rates of misuse and abuse, and of accidental overdose of opioids, have risen over the past decade," said Jenkins. According to FDA, about 3.7 million patients were taking the drugs under scrutiny in 2007. A federal survey conducted that year found 5.2 million people in the U.S. reported using prescription pain drugs inappropriately.

"This is an ongoing problem that's getting worse," said Bob Rappaport, head of FDA's anesthesia drugs division.

FDA said it will meet with 16 drugmakers March 3 to discuss risk-management plans for the medications. Such plans can include bolstered warning labeling, restrictions on patients who can receive the drugs and cautionary letters to physicians.

Companies asked to attend include makers of generic pills as well as brand-name products, like Johnson & Johnson's Duragesic patch, King Pharmaceuticals' extended-releases Avinza pills and Purdue Pharma's extended-release OxyContin.

The risk-managing plans are unlikely to appear until later this year, as FDA said it hopes to hold a public meeting to gather opinions on the issue in the late spring or summer. Until then, regulators said physicians should be diligent about prescribing the drugs only where appropriate.

Regulators said continuing deaths from the drugs are due to both abuse by patients and inappropriate prescribing by physicians. The agency has documented many cases of physicians prescribing the potent painkillers for patients with migraine headaches, an unapproved use. The FDA said patients will also sometimes chew extended-release pills that are designed to be swallowed, causing an overdose of the drug.

The FDA only gained the power to require risk-management plans in 2007, after Congress passed a law designed to improve drug safety. Previously the agency negotiated any changes to drug labeling and promotion with manufacturers.

Regulators are reviewing two experimental painkillers designed to discourage abuse.

King Pharmaceuticals has asked the FDA to approve the drug Embeda, which it acquired through the purchase of Alpharma, as a tamperproof version of morphine for patients with chronic pain. The pills are formulated so that the euphoric effects of morphine are blocked when a patient crushes, dissolves or chews them. Drugmaker Pain Therapeutics, based in San Mateo, Calif., is waiting for an agency decision on its own abuse-resistant version of oxycodone. The drug was developed in partnership with King.

FDA said its announcement Monday only applies to companies with drugs already on the market.