FDA clears emergency use of drug to fight screwworm infections in pets

The U.S. Food and Drug Administration granted emergency use authorization for nitenpyram, a medication to treat New World screwworm infestations in dogs and cats. It is the first generic animal drug approved for use against the flesh-eating parasite. 

Nitenpyram tablets can be used in dogs and cats that weigh at least two pounds and are at least four weeks old, the FDA said in a statement on Thursday. Nitenpyram was previously approved by the FDA in 2000, under the brand name Capstar, for treating fleas.

The FDA relies on emergency use authorizations to speed access to treatments in urgent situations.

The New World screwworm’s larvae eat live flesh and fluids instead of dead material, with females laying their eggs in open wounds and mucous membranes after mating only once in their monthslong lives. The larvae can infest any warm-blooded animal, including wildlife, pets and occasionally even humans.

Studies in Brazil on cats and dogs with screwworm infestations found that most of the maggots were expelled after treatment with nitenpyram, while the remaining larvae died, according to an FDA fact sheet. The agency on Thursday said that after receiving nitenpyram tablets, an animal may need to have remaining live or dead larvae removed by a veterinarian. 

New World screwworm, once an annual warm-weather scourge of cattle ranchers from the 1930s through the 1960s, had been thought to be eradicated in the U.S. Several new cases have been found in cattle in Texas in recent weeks, as well as in a dog in New Mexico, according to government officials.

“Nitenpyram works quickly, killing most [screwworm] larvae within hours of the first dose,” the FDA said on Thursday. “Pet owners should administer a second dose six hours after the first.”

However, because the drug’s effects are short-acting, it does not provide ongoing protection against new infestations, the agency added.