Genetic test info added to epilepsy drugs, U.S. says

WASHINGTON (Reuters) - A genetic test can tell if patients of Asian ancestry are more likely to develop a life-threatening skin reaction to certain drugs that treat epilepsy and other conditions, U.S. health officials said on Wednesday.

Manufacturers of the drugs, which contain the active ingredient carbamazepine, have agreed to add to the prescribing instructions a recommendation that patients of Asian descent get a blood test for a specific genetic variation.

The prescription medicines are Shire PLC's Carbatrol, Validus Pharmaceuticals Inc's Equetro and Novartis AG's Tegretol. The drugs are used to treat epilepsy, bipolar disorder and nerve-related pain.

The move is another step toward "personalized medicine," in which doctors tailor treatments to specific patients.

Patients with an inherited variation of an immune system gene called HLA-B*1502 face an increased risk of rare but potentially fatal skin reactions, the U.S. Food and Drug Administration said.

The reactions include toxic epidermal necrolysis and Stevens-Johnson Syndrome. They can cause multiple skin lesions, blisters, fever, itching and other symptoms.

In countries with mainly white populations, the FDA said, the chances of developing such a reaction is estimated at between 1-to-6 per 10,000 new users of carbamazepine. In some Asian countries, the risk is thought to be about 10 times higher, according to the FDA.

About 5 percent of patients being considered for carbamazepine treatment are of Asian descent, the FDA said. They can have a blood test to check for the genetic variation, which is found almost exclusively in people with Asian ancestry.

Patients who test positive should not be treated with carbamazepine "unless the benefit clearly outweighs the increased risk," the FDA said.

The drugs already carried a warning that all patients who start taking carbamazepine face a risk of rare but serious skin reactions.

The warning will now be moved to a "black box" that appears on the prescribing instructions. The recommendation on genetic testing also will be included in the black box.

Patients who have taken carbamazepine for more than a few months and not had any skin reactions are unlikely to ever experience those problems, regardless of ancestry or genetic test results, the FDA said.

Anyone taking carbamazepine who is concerned about skin reactions should not stop taking the drug without first consulting a doctor, the FDA added.

(Reporting by Lisa Richwine; Editing by Brian Moss)