Vivus Identifies Birth Defect Risk Tied to Weight-Loss Drug Qnexa

Updated with analyst comments, new stock price.

MOUNTAIN VIEW, Calif. (TheStreet) -- The infants of women exposed during pregnancy to a component of Vivus' (VVUS) weight-loss drug Qnexa had a higher rate of oral birth defects compared to infants not exposed to the drug during pregnancy, according to interim study results released Wednesday night.

Vivus shares are down $2, or 19%, to $8.33 in Thursday's pre-market session. The drop in Vivus' share price reflects investor concerns that the higher rate of birth defects observed with the Qnexa component may jeopardize the company's efforts at getting the weight-loss drug approved next year.

Peter Tam, Vivus' president, said in a statement that the prevalance of birth defects detected from Wednesday's study were in line with previously reported studies and that the company was sharing the new data with the U.S. Food and Drug Administration.

Vivus, in its Wednesday night announcement, was careful not to draw any conclusions from the birth defect study and didn't say whether the results made Qnexa's approval any more or less likely. The company isn't holding an investor conference call.

Women in the first trimester of pregnancy who took the epilepsy drug topirimate, one of two active ingredients that make up Vivus' Qnexa, were at a two-fold risk of giving birth to a child with a cleft lip or palate compared to women who also took topirimate previously but not during pregnancy.

The actual rate of oral birth defect in women who took topirimate during pregnancy was 0.29% compared to 0.16% in women with prior exposure to the drug.

In another analysis, pregnant women who took topirimate during the first trimester were five times more likely to give birth to a child with an oral birth defect compared to a control group of pregnant women not exposed to topirimate. Here, the actual rate of cleft lips and palate was 0.36% versus 0.07%, although Vivus said the rate of birth defects in the control group of women may be artificially low due to random error.

U.S. regulators have previously issued safety warnings about the risk of cleft lips and palates in children born to women who took topirimate during pregnancy.

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