The US Food and Drug Administration (FDA) issued a Complete Response Letter to Somaxon Pharmaceuticals, San Diego, for the company’s New Drug Application (NDA) for its insomnia drug Silenor®  (doxepin). After review the FDA determined that the NDA “cannot be approved in its present form.” The FDA raised a number of issues relating to the interpretation of the efficacy data contained in the Silenor NDA.

Although the FDA noted that there were no adverse events observed in the clinical studies included in the NDA that would preclude approval, the FDA asked Somaxon to address the possibility that doxepin may prolong the cardiac QT interval.

The company intends to respond by submitting the results of its completed clinical trial of doxepin that evaluated the potential for electrocardiographic effects to the FDA. The results of this clinical trial demonstrated that doxepin had no effect on QT interval prolongation when administered at 6 mg or 50 mg.

“We continue to believe that the data in the NDA we have submitted, together with the QT data we will submit, is sufficient to support a determination by the FDA that Silenor can be approved for the treatment of insomnia,” said Richard W. Pascoe, president and chief executive officer of Somaxon.

The FDA indicated that it was open to a discussion of the concerns and did not specifically request the company to conduct additional clinical trials of Silenor. Somaxon plans to schedule a discussion with the FDA to gain a complete understanding of the implications of the issues raised in the Complete Response Letter.

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