By Lisa Wade McCormick

June 8, 2008
A reformulated heartworm prevention drug for dogs is making a limited return to the U.S. market.

The U.S. Food and Drug Administration allowed ProHeart 6 Sustained Release Injectable for Dogs, NADA 141-189, manufactured by Fort Dodge Animal Health, back onto the market.

The medication had been withdrawn because of serious, life-threatening adverse reactions, including loss of appetite, lethargy; vomiting, seizures, difficulty walking, jaundice (a yellowish appearance); and bleeding disorders, allergies, convulsions, followed in some cases by death.

FDA is allowing the medication to be prescribed by veterinarians under a risk minimization and restricted distribution program designed to "manage the re-introduction of ProHeart 6 to provide for safe, appropriate use of the product while minimizing risk to dogs."

"This is the first veterinary drug to be marketed under a risk minimization and restricted distribution program. Numerous drugs for use in people have been successfully marketed under similar programs," said Bernadette Dunham, D.V.M., Ph.D., director, FDA's Center for Veterinary Medicine. "While we concur with the limited return of ProHeart 6 to the U.S. market, we strongly encourage veterinarians and pet owners to report any possible adverse reactions."

Heartworm disease is a serious and potentially fatal condition for dogs. The parasite that causes heartworm disease is transmitted through the bite of a mosquito.

The risk minimization and restricted distribution program is intended to educate veterinarians and pet owners regarding the possible risks associated with the use of ProHeart 6. Fort Dodge Animal Health is requiring veterinarians who wish to purchase ProHeart 6 to register with the company and participate in a Web-based training program prior to obtaining the product.

The return of ProHeart 6 to the market is based on results of additional toxicological and pharmacologic studies by Fort Dodge Animal Health coupled with the low adverse reaction frequency in international markets, the FDA said.

Recalled in 2004

In 2004, Fort Dodge Animal Health agreed to recall the product voluntarily based upon FDA's concerns regarding reports of serious adverse reactions in dogs following the use of ProHeart 6.

In response to FDA's concerns, the manufacturer conducted additional testing of its product, which indicated that residues of the solvents used in the manufacture of ProHeart 6 might cause allergic reactions.

The FDA said the manufacturer has improved the manufacturing specifications for ProHeart 6 to decrease the presence of those residues and has marketed the product in international markets. Few adverse events have been reported with this reformulated product.

The ProHeart 6 label and Client Information Sheet have been revised to include updated safety information. The new label includes warnings not to administer the drug within one month of vaccinations, and to use the product with caution in dogs with pre-existing allergic diseases including food allergies, allergic hypersensitivity, and flea allergy dermatitis.

The label also warns against administering the drug to dogs who are sick, debilitated, underweight, or who have a history of weight loss. In addition, the label's Post-Approval Experience section has been updated to include information about adverse reactions based on voluntary post-approval drug experience reporting.

Dog owners who suspect their dog is experiencing an adverse reaction to ProHeart 6 should immediately contact their veterinarian to initiate appropriate veterinary care. Veterinarians should contact Fort Dodge Animal Health to report any adverse events at (800) 533-8536

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