WASHINGTON - ProHeart 6, a twice-a-year time-released
heartworm medication used to prevent the parasite in millions of dogs, was
recalled Friday at the request of the Food and Drug Administration after
thousands of animals suffered adverse reactions.
ProHeart 6 was the first, and only, product approved by
the FDA to be administered once every six months to treat heartworm
disease in dogs. Its active ingredient, moxidectin, has been administered
without problem to horses and cattle.
The time-released version caused few problems when given
to dogs at higher doses in clinical trials. Health and safety problems
quickly cropped up, however, when ProHeart 6 was used to treat dogs after
receiving FDA approval.
As of Aug. 4, the drug agency received 5,552 reports of
adverse reactions after dogs received heartworm shots. About 500 dogs
died, though the agency said many deaths were not directly attributable to
the product, manufactured by Fort Dodge Animal Health, based in Overland
Park, Kan., a subsidiary of the pharmaceutical company Wyeth.
Some dog deaths were linked convincingly to the heartworm
medication, which prompted the recall, said Stephen F. Sundlof, director
of the FDA's Center for Veterinary Medicine.
Dog owners were urged to consult veterinarians about other
medications to prevent heartworm.
The agency had already asked Fort Dodge to revise the
drug's label and to issue notices to veterinarians and dog owners pointing
out safety questions associated with the product.
"Despite all of the things that have been done, we
continue to see these adverse events at approximately the same rate,"
Sundlof told reporters late Friday.
The problems suffered by dogs include sudden lethargy,
uncontrolled bleeding, vomiting, diarrhea, heart and liver problems and
such nervous system abnormalities as seizures.
"We don't really understand why this product is causing
these problems," Sundlof said. "It affects dogs of all sizes and,
apparently, dogs of all ages."
Fort Dodge Animal Health is cooperating with FDA's request
for a recall but has "concerns about how the agency interpreted these
complex data," the animal health product manufacturer said in a prepared
statement. "Based on a thorough evaluation of FDA's data and consultation
with independent experts in veterinary medicine and
epidemiology, Fort Dodge Animal Health stands behind ProHeart 6."
The FDA will convene an independent scientific advisory
committee to review the matter.
Heartworm disease is caused by a parasite transmitted to
dogs via mosquito bite. Roughly 250,000 dogs develop the potentially fatal
ailment per year. Fort Dodge Animal Health said it has sold 18 million
doses of ProHeart 6 to veterinarians since FDA approval in June 2001.
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