Economic realities depleting arsenal of antiparasitic drugs

October 29, 2000

While resistance may be reducing the effectiveness of our medicine chest, we have another force to fear: economics. Many drugs still effective against parasitic diseases are either no longer available, no longer manufactured or in danger of being pulled from the market simply because they are not economically viable, say researchers from the Baylor College of Medicine and Centers for Disease Control and Prevention (CDC) at a presentation during the annual meeting of the American Society of Tropical Medicine and Hygiene.

"Parasites are a very common causes of disease in the world but because there is no market for antiparasitic drugs, drug companies are discontinuing production," says Clinton White of the Baylor College of Medicine in Houston.

By the phrase "no market" Dr. White does not mean that parasites do not cause signficant disease, but that these diseases are most commonly found in developing countries that do not have the money to effectively support production of these drugs. In addition, many drugs that are available overseas are used to treat infections that are only found occasionally in the United States making them prohibitively expensive to continue domestic production despite their necessity for a small population of Americans. Dr. White and his colleague Anne Moore from CDC first began looking into this phenomenon last summer when a number of clinicians noticed that they were having a hard time acquiring the drug praziquantel which is used to treat schistosomiasis, a parasitic disease that can cause chronic liver damage and affects an estimated 200 million people worldwide. The drug's manufacturer had simply stopped making it in the United States because it was losing money.

"Here we had a perfectly treatable infection and no access to a drug to treat it in this country," says White. The maker of praziquantel has since agreed to resume production, but White and Moore have found numerous similar instances where effective drugs are no longer being made available in the United States, and sometimes worldwide, because they are not economically viable.

In one case they found a drug still being used that hasn't been in production for over 20 years. Bithionol is used to treat infection with Fasciola, a parasite also known as the liver fluke that can cause severe liver damage. The company that made bithionol, though, discontinued production in 1979. The CDC now has the only U.S. supply of this drug and distributes it on an as-needed basis. The Food and Drug Administration has tried to take steps toward remedying the situation in general, says White, but more needs to be done.

"We have to recognize that parasitic diseases are a real public health problem, but that the market for financially sustainable drugs just isn't there," says White. "We need to offer federal support for development of these drugs, including tax advantages for research into human indications for veterinary drugs."

Parasitic infections are commonly found in pets and the pharmaceutical industry has found this to be a financially lucrative area that may offer support for some human drugs. For example, one drug that is commonly used to treat heart worms in dogs is also effective against a number of parasitic diseases including river blindness. The manufacturer of that drug for veterinary purposes has found it to be so profitable that they have been able to give the drug away free in developing countries.

Another way to address the situation is through the CDC, says White. The CDC has a parasitic diseases drug service, through which it currently distributes bithionol and other drugs. The government should give the drug service a clear mandate to ensure the availability of these drugs in the future and the funds necessary to achieve that goal.

"More and more the population is traveling to areas where parasitic diseases are endemic. If you have an infection you got overseas, you're going to need these drugs to treat it here in the United States," says White.
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The American Society of Tropical Medicine and Hygiene (ASTMH) is the principal organization in the United States representing scientists, clinicians, and others with interests in the prevention and control of tropical diseases through research and education. Additional information on the meeting can be found at http://www.astmh.org/presskit.html.

American Society for Microbiology

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