Advisers to the Food and Drug Administration said Friday a blood-clotting drug from GlaxoSmithKline and Ligand Pharmaceuticals is effective for short-term use, despite reservations by FDA scientists.

A panel of outside advisers voted unanimously in favor of Promacta at a meeting held in Chicago, according to FDA spokeswoman Karen Riley. The drug is designed to treat an immune system disorder that causes the body to destroy its own platelets, which can cause excessive bleeding.

The decision sent shares of San Diego-based Ligand soaring more than $1.25, or 53 percent, to $3.58. Shares of GlaxoSmithKline PLC rose 57 cents, or 1.30 percent, to $44.55.

Panel members noted that the companies have not provided long-term data on the drug, but said results from two, six-week studies appeared to show significant benefit. Long-term studies should be available by the end of the year, according to the companies.

British drugmaker Glaxo and partner Ligand want Promacta approved to treat patients’ with chronic idiopathic thrombocytopenic purpura, which causes excessive bruising and bleeding. About 60,000 people in the U.S. have the disease, according to Glaxo.

FDA has until June 19 to make a final decision on the drug. It is not required to follow the advice of its outside panel though it often does.

The panel’s opinion came as a surprise to Wall Street, since FDA had released its own negative review of the drug earlier in the week. That news on Wednesday walloped Ligand’s shares, sending them to $2.16, their lowest point in at least 10 years, to recover by end of day down 36 percent to $2.30. The company has been a Glaxo partner since 1997.

Agency reviewers said that the drug did not significantly lower bleeding compared with a placebo in two studies submitted by the companies.

FDA scientists also raised concerns about liver toxicity and the drug’s safety in long-term use.