The Food and Drug Administration (FDA) on Jan. 5th announced the approval of Pfizer's Slentrol (dirlotapide) as the first prescription diet drug for obese dogs.

Slentrol -- which the FDA emphasizes is NOT for use in humans -- reduces the appetite of dogs and their fat absorption to produce weight loss. The label of Slentrol cites adverse reactions in humans that include abdominal distention, abdominal pain, diarrhea, flatulence, headache, nausea and vomiting.

"This is a welcome addition to animal therapies, because dog obesity appears to be increasing," said Stephen Sundlof, D.V.M., Ph.D., director of FDA's Center for Veterinary Medicine.

Slentrol is a new chemical entity called a selective microsomal triglyceride transfer protein inhibitor, which blocks the assembly and release of lipoproteins into the bloodstream.

The FDA said the mechanism by which this produces weight loss in dogs is not completely understood, but seems to result from reduced fat absorption and a satiety signal from lipid-filled cells lining the intestine.

Adverse reactions associated with treatment of dogs with Slentrol include vomiting, loose stools, diarrhea, lethargy and loss of appetite.

Veterinarians generally define a dog that weighs 20 percent more than its ideal weight as obese. Surveys have found that approximately 5 percent of dogs in the United States are obese, and another 20-30 percent are overweight.

"Veterinarians are well aware that overweight pets are at a higher risk of developing various health problems, from cardiovascular conditions to diabetes to joint problems," Sundlof said.

The drug is given to the dog in varying amounts over the course of the treatment. The dog is given an initial dose for the first 14 days. After that, the veterinarian will assess the dog's progress at monthly intervals, adjusting the dose depending on the dog's weight loss.