Array BioPharma skids on side effects of pain drug

NEW YORK (AP) -- Shares of Array BioPharma tumbled Wednesday after investors became concerned about some side effects of an experimental pain drug, though the drug in the most recent clinical trials appears to work.

Array reported results from the mid-stage trial of ARRY-797 after the market closed Tuesday. The company said the drug was better than a placebo at reducing moderate to severe pain caused by osteoarthritis of the knee, and the drug worked about as well as the pain drug oxycodone. However Array said some patients experienced heart side effects that can increase the risk of arrhythmia, a problem with the rate or rhythm of the heartbeat.

One analyst said potential side effects could hurt sales and potentially the company's chances of landing a partnership to market the drug.

Array does not have any products on the market, and ARRY-797 is its most advanced drug candidate. Shares of the Boulder, Colo., company dropped 60 cents, or 11.7 percent, to $4.54 in early trading.

The four-week trial evaluated ARRY-797 in patients for which non-steroidal anti-inflammatory drugs like aspirin and ibuprofen did not work. All patients continued taking those drugs during the study in addition to taking ARRY-797, oxycodone, or a placebo.

Some patients had "mild prolongations of QTc interval," the study found, which is a measurement of the time it takes the heart to recalibrate its electrical signal before pumping. A longer interval is associated with increased risk of arrhythmia.

Array is conducting additional studies of the drug on healthy volunteers to learn more about its effects on the heart rate. Patients in the main study took 400 milligrams of ARRY-797 twice a day, and in the safety study, patients are taking as much as 1000 milligrams twice a day. The company said longer QTc intervals were observed in patients who took the larger doses in the safety trial.

"These QTc observations warrant further evaluation," the company said in a press release. Array said the increased QTc intervals fell short of guidelines are linked to significantly increased risks for arrhythmia.

Jefferies & Co. analyst Eun Yang said the side effect "could potentially pose a challenge to a lucrative partnership opportunity for chronic/broad use."

The most common side effects of treatment with ARRY-797 were diarrhea, and nausea. According to Array BioPharma Inc., most of the side effects were mild. Array is also studying treatments for asthma and cancer. The company's shares have climbed 47 percent since July 13.

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Array BioPharma skids on side effects of pain drug