Efforts by Indevus Pharmaceuticals ( IDEV) to land U.S. approval for a long-acting testosterone have been delayed by two years, news that sent the stock falling to a new 52-week low Wednesday morning.

The Lexington, Mass.-based specialty pharmaceutical firm revealed that the U.S. Food and Drug Administration has asked for additional safety data on Nebido, a long-acting injectable testosterone.

Indevus will be required to conduct a new clinical trial to collect the safety data, which the biotech company estimates will take 18 months to complete. The FDA was expected to issue its approval decision on Nebido later this month, so the delay pushes the timeline for the product's approval out two years.

Indevus shares slumped $2.72, or 66%, to $1.38 in recent trading Wednesday morning. Before today, the stock had traded only as low as $3.91in the last 52 weeks and as high as $8.22 in the same time.

Nebido is an every-three-month injectable testosterone for the treatment of male hypogonadism, the failure to produce adequate amounts of the male reproductive hormone.

Current testosterone treatments are administered via creams, gels or more frequent injections.

According to Indevus, the FDA's safety concerns centers around an adverse reaction to the Nebido injection that can cause patients to cough or suffer shortness of breath. This short-term reaction was seen in only one patient out of 500 patients enrolled in the Indevus clinical trials.

"We are very surprised and disappointed by the position the FDA is taking regarding the safety profile of Nebido given the large European experience," said Indevus CEO Glenn Cooper, in a statement. "Rare coughing reactions have been well described in the European product labeling of Nebido. We believe the information available on these cases indicates these reactions resolved without consequences and that our proposed labeling for Nebido in the U.S. adequately addressed this issue."

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