On Monday, FDA officials released a draft compliance policy guide (CPG), a document that is not legally enforceable but reflects current thinking on the topic of therapeutic diets. It directs FDA staff and industry on how the agency intends to use its enforcement discretion — leeway that allows therapeutic diets to be regulated as food even though FDA officials believe they should be considered drugs because of their intended effects.

According to the Sept. 10 Federal Register, the public has until Nov. 9 to review the draft CPG and submit comments to the FDA for consideration. Written comments on the draft CPG can be mailed to the Division of Dockets Management (HFA-305), Food and Drug Administration, 5630 Fishers Lane, Room 1061, Rockville, MD 20852.

CPG background materials report that during the past 24 years, the FDA's Center for Veterinary Medicine (CVM) has observed an uptick in numbers of pet foods carrying therapeutic claims, sold with or without the direction of a licensed veterinarian. The shift in marketing directly to pet owners "is of concern because many of these products affect physiological processes to extents that may not be tolerated by all animals and/or may not achieve effective treatment," the agency said.

So far, manufacturers have remained quiet about the CPG. Phone calls late Friday to the Pet Food Institute, billed as "the voice of pet food manufacturers," were not immediately returned.

The FDA did not list brands targeted but noted that officials are paying special attention to pet foods with labels that explicitly or implicitly indicate diseases for which the product is to be used. By the agency's definition, therapeutic diets are those that promise to "diagnose, cure, mitigate, treat or prevent diseases." Such pet foods are subject to regulatory oversight and have been around for half a century.

Often, a fine line exists between the therapeutic brands on store shelves and those sold in veterinary practices. For example, Hill’s — a pet food maker that’s trademarked the term “prescription diet" — sells two brands designed to control the weight of dogs and cats.

Hill’s Prescription Diet r/d is so low in calories, it’s not recommended for long-term feeding and is sold through veterinary practices. By contrast, Hill’s Science Diet Light is sold in stores because the company deems its ingredients to be more balanced and suitable for extended use without a veterinary directive.

Apparently, the FDA doesn't want to leave such designations to manufacturers. In the CPG, the agency said it's going to pay special attention to therapeutic diets sold in retail sectors without the guidance of veterinarians.

Dr. Jennifer Larsen, assistant professor of clinical nutrition at the University of California, Davis School of Veterinary Medicine, describes the issue of therapeutic diets as "complex."

"Certainly, the FDA CVM is on record saying therapeutic diets are essentially unapproved drugs, but with the Internet, these diets are increasingly sold directly to the general public," she said. "At the same time, labels are becoming more descriptive about their intended purposes. All this marketing is muddying the issue and the main question: Should these diets require a prescription?"

Larsen frequently uses therapeutic diets in practice but first requires approval from the patient's primary veterinarian before dispensing such foods. "We've had instances where animals had gotten into big trouble and almost died because they were given the wrong diet by accident," she said. "There is a potential for harm, and I think most veterinarians recognize that."

Officials within the FDA CVM worry that consumers might falsely believe that foods designed to control blood glucose, for example, can act as the sole treatment required for diabetic pets that might need insulin therapy or other treatments.

Those concerns dissipate when therapeutic dog and cat food diets are marketed through and used under the direction of a licensed veterinarian. "The agency presumes the veterinarian will provide direction to the pet owner for how to use the product including periodic assessment of the product's effectiveness in both treatment outcome and provision of adequate nutrition of the animal," the FDA states in its draft CPG.

The FDA proposes to continue allowing therapeutic diets to be sold without going through the agency's costly and cumbersome regulatory approval process if the following factors are in place:

The parameters seem "reasonable" to Dr. Joe Bartges, a professor of medicine and nutrition at the University of Tennessee's veterinary college.

"My interpretation is that if a diet is 'therapeutic' in nature, then it should be used with oversight by a veterinarian," Bartges said by email. "It seems to me that part of this CPG is providing safety for pets when using modified diets for conditions, and another part is making sure there is some regulation and oversight."

A statement by Dr. Bernadette Dunham, head of the FDA CVM, bolsters Bartges's assessment. In December 2010, Dunham said publicly that the FDA considered therapeutic diets to be equivalent to prescription drugs, thereby coming under the agency’s purview. She noted that diets labeled therapeutic or prescription needed to come from a veterinarian’s office and should require a prescription.

Her statements, however, confused veterinarians and later were partially redacted.

Many veterinarians do not treat therapeutic diets as seriously as prescription drugs because the terms “prescription” or “therapeutic” is viewed by some as lingo used to falsely brand pet foods as medicinal. In response to Dunham's 2010 announcement, Dr. Wesley Borgman, a practitioner near Orlando, told the VIN News Service that it’s not uncommon for practitioners in his area to sell therapeutic diets to vacationing owners without prescriptions or examinations.

"The FDA doesn't regulate nutraceuticals. These diets are just one big nutraceutical," he reasoned.

Lawmakers tend to agree with the notion that therapeutic pet diets are not prescription medications, especially in states where drugs are exempt from sales taxes. In Florida, for example, veterinarians and their clients can avoid sales taxes only on products that carry the label, “Caution: Federal law restricts this drug to sale by or on the order of a licensed veterinarian."

If the FDA has its way, bags of pet food could one day bear that statement.

Dunham’s comments in 2010 mirror the view of Dr. William J. Burkholder, head of the FDA-CVM’s Division of Animal Feeds. In 2003, Burkholder authored an article published in the Journal of the American Veterinary Medical Association in which he characterized therapeutic diets as “illegal” products because they have not been proven safe and effective for their intended uses.

The CPG takes Burkholder's view on therapeutic diets a step further: "FDA is concerned that listing a disease or symptom on the label of a product does not provide a pet owner with sufficient information on the effectiveness, possible side effects and contraindications for use of the product and that, in the absence of a valid veterinarian-client-patient relationship, pet owners may misuse such a product, resulting in harm to their pets."