A blood-thinning drug not approved for the U.S. market because of questions about liver damage appears to be as effective as other common therapies for preventing strokes and recurring blood clots, according to studies published on Tuesday.

The drug, ximelagatran, is of interest because it is taken orally and is simpler to administer than current anti-coagulation therapies that in part require injections. It has been approved for short-term use in parts of Europe.

Tuesday’s studies, both published in the Journal of the American Medical Association, were paid for by AstraZeneca, which is developing the drug under the brand name Exanta.

One study, from Hopital Europeen Georges Pompidou, Paris, found the drug as effective for treating recurrent blood clots in the veins of the legs, pelvis or arms as standard therapy using the anticoagulants enoxaparin and warfarin.

The drug did not require adjustment of doses or monitoring patients for coagulation, but some of the patients showed higher levels of an enzyme that can indicate liver damage.

In the second study, researchers at Mount Sinai Medical Center, New York, found ximelagatran as effective as warfarin for prevention of stroke in patients with atrial fibrillation - a heart condition linked to abut 15 percent of all strokes.

The researchers said warfarin cuts stroke risk by 62 percent but the risk of bleeding limits its use, particularly among the elderly. The second study also detected possible liver damage with ximelagatran.

Commenting on the studies in an editorial in the same issue, Dr. Victor Gurewich, of Beth Israel Deaconess Hospital Medical Center, Boston, said more clinical trials are unlikely to resolve the question of the drug’s adverse effects.

“Diligent postmarketing surveillance is essential to monitor use and to determine the risks associated with this agent, and this may be the best, if not the only, way to deal with this question,” he added.

He said the U.S. Food and Drug Administration, “perhaps feeling the effects of recently having to withdraw drugs from the market,” has denied approval of ximelagatran because of possible liver problems.

“However, this precaution…must be balanced against the serious risk of discouraging, if not foreclosing indefinitely, any improvement in oral anticoagulant therapy, which remains an important and growing therapeutic need.”