Monthly chewable tablet for screwworm in dogs receives conditional approval

The Food and Drug Administration (FDA) continues to build up veterinarians' arsenal against New World screwworm (NWS), should it cross the U.S.-Mexico border.

On December 17, the FDA conditionally approved Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, and pyrantel) monthly chewable tablets for the treatment of infestations of NWS (Cochliomyia hominivorax) larvae in dogs and puppies at least 8 weeks of age and weighing at least 3.3 pounds.

This comes after recent emergency use authorizations for two animal drugs for NWS: Credelio and Credelio Cat for dogs and cats, respectively, and another conditional approval for Exzolt Cattle-CA1 (fluralaner) topical solution in cattle.

Screwworm's northward migration from Central America has prompted a massive response from animal health officials, who have called for heightened vigilance from small and large animal veterinarians to ensure the parasite, declared as eradicated in 1966, does not regain a foothold in the U.S.

Credelio Quattro CA-1, available only by prescription from a licensed veterinarian, comes in five strengths of flavored chewable tablets with active ingredients by weight.

The minimum dosage is 9 mg per lb (20 mg/kg) lotilaner, 0.009 mg per lb (0.02 mg/kg) moxidectin, 2.28 mg per lb (5 mg/kg) praziquantel, and 2.28 mg per lb (5 mg/kg) pyrantel (as pamoate salt). Dogs over 100 lb should be given the appropriate combination of chewable tablets, according to the FDA.

Credelio Quattro-CA1 must be orally administered with food. The FDA says care should be taken to ensure that the dog consumes the complete dose and that if vomiting occurs within an hour after administration, readminister a new dose.

Credelio Quattro and Credelio Quattro-CA1 contain the same active ingredients at identical doses: lotilaner, moxidectin, praziquantel, and pyrantel.

Credelio Quattro, sponsored by Elanco Animal Health, is already approved for various flea-, tick-, and worm-related indications in dogs and puppies.

The conditional approval was based on a study evaluating the efficacy of lotilaner against New World screwworm, according to the company, which said a peer-reviewed study showed oral administration of the antiparasitic drug at the minimum recommended dosage demonstrated 100% efficacy against NWS larvae within 24 hours of treatment in naturally infested dogs.

A single dose of Credelio Quattro-CA1 is "reasonably expected" to treat NWS larvae present at the time of treatment, though reinfestation may occur sooner than one month, according to Elanco's application for conditional approval. "Treatment should be used in conjunction with the mechanical removal of larvae (live and dead) remaining in the wound after treatment."

While livestock are most commonly affected, NWS can infest all warm-blooded animals, including wildlife, pets, and even humans. Still, most dogs in the U.S. remain at low risk of contracting NWS due to their geographic location, though animals near the U.S.-Mexico border and those that travel to countries with active cases are at higher risk of exposure.

"As a veterinarian, I'd encourage pet owners to monitor for any wounds on their dogs as even a minor scratch could serve as an entry point for New World screwworm," said Dr. Casey Locklear, parasitology lead at Elanco, in the company announcement. "I also recommend pet owners keep their dogs on year-round parasite protection like Credelio Quattro to help minimize self-inflicted scratching that could create vulnerable sites."