NEW YORK (AP) _ More than a half-million emergency injection kits for treating severe allergic reactions and asthma attacks are being recalled in the United States and Canada because the drug may not work.

The kits are routinely carried by people who are prone to acute asthma attacks or have deadly allergies to certain foods or bee stings, for example. Users inject themselves with epinephrine, also known as adrenaline, to counter the reaction.

The maker of the epinephrine, American Home Products' Wyeth-Ayerst Laboratories, said Tuesday that routine quality-control tests found that the drug was not as potent as it was supposed to be. No one has been harmed by the kits, a spokesman said.

The recall involves three kits: the Insect-Sting Treatment Kit packaged and distributed by Derm/Buro Inc., and the Hollister Stier-Ana-Kit and the Ana-Guard, both packaged and distributed by Bayer Corp.

All of the kits are sold by prescription and cost around $40.

The kits should be returned to the hospital, clinic or pharmacy where they were obtained, American Home said.

Philip de Vane, North American medical director for Wyeth-Ayerst, said people should take no chances and should contact their pharmacists or health care providers to determine whether their kit is being recalled.

Consumers can call Wyeth-Ayerst at 1-800-999-9384.

About 450,000 Ana-Kits and 55,000 Ana-Guards are being recalled, said Kathleen Bauernschmidt, spokeswoman for Hollister-Stier Laboratories of Spokane, Wash. Bayer sold its allergy kit manufacturing business to Hollister-Stier in June. It was unclear how many kits were being recalled by Derm/Buro.

People who are prone to allergic reactions can suffer what is known as anaphylactic shock, in which swelling of the airways can cut off breathing and the heart can stop. Epinephrine, a naturally occurring hormone, is used to increase blood flow and restore breathing.

The number of kits being recalled represents about 25 percent of all allergic reaction kits on the market, Ms. Bauernschmidt said.

The recall is just the latest setback for American Home, which faces legal problems over its diet drugs and Norplant contraceptive device.

Overall, shares of American Home have fallen more than 40 percent this year because of the rash of problems. On Tuesday, the stock dropped 56 1/4 cents to $41.43 3/4 on the New York Stock Exchange.

Last week, American Home agreed to pay a reported $50 million-plus to settle claims from 36,000 women who said Norplant caused headaches, irregular menstrual bleeding, nausea and depression.

In August, a jury awarded $23 million to a Texas woman who claimed the company failed to warn her about the dangers of American Home's diet drugs Redux and Pondimin, which is part of the drug combination fen-phen. Hundreds of lawsuits are now pending nationwide against the company over the drugs' potential to cause heart-valve problems.

The company this summer suspended shipments of a childhood diarrhea vaccine after it was linked to bowel obstruction in 32 infants. And last year, American Home recalled the painkiller Duract after it caused fatal liver problems.

The allergy kit recall affects: Derm/Buro Insect-Sting Treatment Kits with the lot numbers 0397, 0497, 0597, 8141, 8139, 11464, 13239. The products were distributed between June 1997 and February 1999.

Also affected: Ana-Kits with lot numbers AK344 through AK363 and lot AK366, and Ana-Guard with lot numbers G00196 through G00220, and lots G00222 and G00223. They were distributed by Bayer between April 1997 and April 1998.