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What's a Rare Disease for Dogs? FDA Proposes Maintaining Current Levels for Major Species

Posted 19 May 2014 | By Alexander Gaffney, RAC

What's a Rare Disease for Dogs? FDA Proposes Maintaining Current Levels for Major Species

Drug regulation is in many ways as much about incentives as it is about requirements. Especially for drugs intended for smaller populations, an incentive—a free review voucher or a speedy review time, for example—may be the difference between a drug existing as a concept or as one available to consumers.


In the US, patients have long benefited from the Orphan Drug Act, which defines a rare disease as one affecting fewer than 200,000 patients in a given year and offers regulatory incentives to companies whose drugs meet the requirements of the law. But crucially, the Orphan Drug Act applies to just one species: humans.

For animals, the definition of "rare" takes on an entirely different meaning. That's because rather than dealing with one species—humans—animal drugs must account for thousands of different species. How, then, can the regulatory framework account for rare diseases which affect a small number of animals and might not otherwise attract investment from companies?

The answer lies in the Minor Use and Minor Species Animal Health Act (MUMS Act), a 2004 law which treats animal health conditions as rare if they meet one of the following two requirements:

  • It affects a "major" animal species—cattle, horses, swine, chickens, turkeys, dogs, and cats—but in a quantity or distribution insufficient to spur investment, meaning it would only receive "minor use.”
  • It affects a "minor" species (i.e. not a "major" species) in any capacity.

Drugs which meet the law's terms are eligible for three years of market exclusivity, during which time the same drug may not be marketed for the same use.

Defining Rarity

Unlike the Orphan Drug Act, the MUMS Act doesn't actually define the quantity of what "infrequently" means for the purposes of disease incidence.

Instead, the US Food and Drug Administration (FDA) is charged with periodically updating a definition of "small number of animals" for the purposes of the act's "major species" provisions.

On 19 May 2014, FDA announced that it is reassessing its definitions under the MUMS Act and is seeking public input on its list, which was last updated in August 2009.

As FDA explained, the "small number of animals" definition is far more complex than first meets the eye.

"Such a reevaluation should take into account the potential for increases in the development cost of new animal drugs, but note that it also should take into account potential increases in the cost that animal owners are willing to pay to treat affected animals as well as other factors involved in establishing 'small numbers,' such as changes in the total population of major animal species," FDA wrote.

Different considerations also exist for food-producing animals and companion animals, FDA noted.

In other words, it's all about incentivizing development, taking into account all of the factors which drive that development.

New Factors, Old Definitions

However, even as factors have changed over the last five years, FDA said it has determined that its current definitions have held up since the last update, and it has proposed to maintain those definitions at their current levels:

Current MUMS Act Definitions of "Small Number of Animals"

Comments to FDA about the MUMS definitions are due at any time.

Federal Register Notice

CVM Announcement


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