["Is this the demise of \"lite\" petfoods? - David Dzanis", "The fat molecules get into the intestinal cell but can't get out as easily."]

During the 2007 Forum of the American College of Veterinary Internal Medicine in Seattle, Washington, USA, I attended some interesting presentations regarding a new drug for weight control in dogs (Kirk et al., 2007). Slentrol (dirlotapide), a microsomal triglyceride transfer protein inhibitor, was approved in the US for management of canine obesity in February 2007. A similar drug (Yarvitan) has been approved in Europe.

While Slentrol is a welcome addition to the arsenal to fight canine obesity, it is not a panacea, and traditional methods of calorie control via dietary modification still will be required.

How does it work?

Briefly, dirlotapide partially blocks the proteins in the cells lining the intestine that are responsible for transfer of fat molecules into the body, thus keeping those proteins from working efficiently. In other words, the fat molecules get into the intestinal cell but can't get out as easily. This buildup of fat in the cells then triggers a hormone that tells the brain, "I'm full." The result is the dog is not as hungry as usual and simply eats less.

Appetite suppression accounts for approximately 90% of the drug's function. The rest is due to the normal sloughing and replacement of the intestinal lining cells. The sloughed fat-laden cells are then excreted in the feces, resulting in a loss of some of the fat that would normally have been absorbed into the body. However, this is not as extreme an effect as that from drugs that simply block absorption of fats from the intestinal lumen or from foods made with nondigestible fats (e.g., olestra), where oily feces reportedly could become a problem.

How is it used?

A veterinarian must examine the dog to determine health and suitability for treatment. Slentrol is not recommended for dogs with liver disease or on long-term corticosteroid treatment and has not been studied in dogs under 1 year of age or those that are breeding, pregnant or lactating. While reported side effects are mild and often resolve over time, there may be cases where continued use may not be advised. It is strongly cautioned not to use this drug in cats or people, as potentially very serious side effects could occur.

An initial dose is determined, which is adjusted periodically to achieve an effective but safe rate of weight loss. During this treatment phase, the dog's regular food does not need to be changed to a "lite" or lower calorie food. In fact, the presenter considered it ill-advised to switch diets; the ideal is to allow the drug to do its work without other alterations in the dog's routine.

After the dog has reached the desired weight, though, the weight management phase is critical. This is because once the drug is discontinued, the dog's appetite will return with a vengeance. Thus, rebound weight gain can be a considerable problem if the dog is not adjusted to a more fitting calorie intake pattern before the drug is withdrawn.

Impact on the industry

It's during the management phase (recommended three months minimum) of use of dirlotapide that dietary choices, food quantities and exercise regimens appropriate to maintain proper weight must be determined. Lesser amounts of the same food as fed previously may suffice, but in many cases a lower calorie dog food may be a better choice for long-term benefit and pet satisfaction.

This does not have to necessarily be a lite or even "less calorie" food, though. There are many foods intended for maintenance of adult dogs that may be suitable alternatives. The market is replete with products bearing claims for weight management or control, but since they circumvent the current Association of American Feed Control Officials (AAFCO) regulations requiring calorie content statements for lite and less calorie foods, that information most often does not appear on the label. I believe this greatly diminishes the choices dog owners have to select and use an appropriate food.

Fullest potential benefit

As previously discussed in this column, the American College of Veterinary Nutrition (with me as its representative in front of AAFCO) has proposed changes to the Model Pet Food Regulations to require calorie content statements on all dog and cat food labels. The fate of this proposal has not been determined as of this time (seep. 8), but it is my opinion that if passed by AAFCO, it would help pet owners and veterinarians tremendously in choosing the most appropriate food for the management phase and eventually post-treatment. More importantly, it would help in using the chosen product to its fullest potential benefit.

Successful weight maintenance benefits not only the dog and its owner but ultimately the petfood industry as a whole. Consumers will be happier with the performance of products, translating to repeat sales.

In any event, limited calorie petfoods will continue to have a purpose on the market. Some dogs (and all cats) will not be able to take the drugs presently approved, and it's doubtful that will change in the near future. Even for dogs that do achieve weight loss through dirlotapide or similar agents, the need for calorie controlled diets will remain if long-term success is to be anticipated.