(The Associated Press) --The government on Monday approved sale of the first treatment for a miserable infection spread through contaminated drinking water and dirty swimming pools -- a drug called Alinia intended especially for children sickened by the bug.

It's highly unusual for the Food and Drug Administration to clear a new drug for children before it has been okayed for adults to use. But the agency said manufacturer Romark Laboratories proved the liquid kids' version of its drug worked before it provided similar proof for adult-strength Alinia tablets.

The drug treats diarrhea caused by cryptosporidium, a parasite spread by human and animal waste most common in developing countries but that the Centers for Disease Control and Prevention estimates causes up to 4,000 infections a year here, too. The biggest outbreak, in 1993, killed 100 people and sickened 400,000 when cryptosporidium contaminated Milwaukee's water supply.

The chlorine that kills most germs in water doesn't kill cryptosporidium -- it must be filtered out. In addition to drinking water, the bug also can contaminate swimming pools, mostly because of children's diaper leaks.

Most healthy people will be well on their way to recovery before a doctor's visit and lab tests diagnose cryptosporidium so they could take Alinia, said Dr. Dennis Juranek, a CDC senior scientist.

But in some people, particularly those with weak immune systems, the infection can be life-threatening -- and having a drug available in the midst of a large outbreak could be very important, he said.

Here's the rub: The FDA cautioned that study of children with the AIDS virus found no benefit from three days of Alinia. HIV patients may need longer treatment or higher doses, but it will take more study to determine that, said FDA's Dr. Renata Albrecht.

Despite that caveat, Alinia's approval is exciting, Juranek said.

"There have literally been hundreds of drugs tried and none seemed to work at all, so to find one that works even in certain circumstances is important," he said.

Alinia, known chemically as nitazoxanide, also treats a similar waterborne parasite, called giardia. There is an adult treatment for giardia infections, but Alinia becomes the first U.S. therapy specifically for children.

The drug apparently works by blocking enzyme reactions essential for these parasites to thrive inside people.

Alinia was studied in 95 children infected with cryptosporidium in Zambia and Egypt. The drug proved 56 percent and 88 percent effective, respectively, in alleviating the diarrhea. The drug was less effective in the Zambian study because those children were malnourished, FDA said.

In a study of 110 children infected with giardia in Peru, Alinia proved 85 percent effective.

Alinia seems to have no serious side effects, but the FDA cautioned that it has been studied only in several hundred children so far.

The prescription-only drug will reach pharmacies in February. Tampa, Fla.-based Romark wouldn't reveal the price.

Company president Marc Ayers said Romark hopes to sell Alinia tablets for adults next year as well, after completing an additional study that the FDA ordered to be sure they work.

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