The U.S. Food and Drug Administration made history Friday as it approved the first drug made with materials from genetically engineered animals, clearing the way for a new class of medical therapies.

GTC Biotherapeutics said regulators cleared its drug ATryn, which is made using milk from goats that have been scientifically altered to produce extra antithrombin, a protein that acts as a natural blood thinner.

The drug's approval may be the first step toward new kinds of medications made not from chemicals, but from living organisms altered by scientists.

Similar drugs could be available in the next few years for a range of human ailments, including hemophilia.

The FDA cleared the drug to treat patients with a rare hereditary disorder that causes a deficiency of the protein, putting them at higher risk of deadly blood clots. The injectable treatment will be sold in the U.S. by Deerfield, Ill.-based Ovation Pharmaceuticals.

About one in 5,000 people don't produce enough antithrombin protein, according to Framingham, Mass.-based based GTC. As a result, their blood is more likely to stick together, occasionally causing clots that can travel to the lungs or brain, causing death.

Clots threaten placenta

Pregnant women with the disorder are at higher risk of miscarriage or stillbirth, because of blood clots in the placenta.

Patients with hereditary antithrombin deficiency are currently prescribed conventional blood thinners, like Plavix from Bristol-Myers Squibb and Sanofi-Aventis. That will not change with the new approval.

ATryn is only approved for use when patients are getting surgery or having a baby, times when the risk of dangerous clots is particularly high. Those patients would receive the drug by intravenous infusion for a limited time before and after their procedures.

To make the drug, scientists at GTC put DNA for the human antithrombin protein into single-cell embryos of goats.

Goat embryos with the gene were then inserted into the wombs of surrogate mothers, who gave birth to baby goats that produce the protein-charged milk.

Genetically engineered animals are not clones but rather animals that have had their DNA changed to produce a desirable characteristic.

Amid growing questions about the technology, the FDA last month issued guidelines for how it will regulate products made from genetically altered animals.

FDA said it will not allow any such products to be sold without first submitting them to scrutiny by independent advisers at a public meeting. The agency's panel of blood product experts recently concluded ATryn was safe and effective.

But consumer groups said the FDA's long-awaited policy will not require all genetically engineered foods to be labelled as such. And they said the government has not done enough to examine the potential impact of genetically engineered animals on the environment — particularly if some escape and begin to mate with animals in nature.

The drug received European approval in 2006.

Shares of GTC Therapeutics rose five cents, or 5.5 per cent, to 87 cents in midday trading.