Vivus will have to wait a bit longer before getting US approval for its obesity drug Qnexa.

The US Food and Drug Administration has extended the action date by three months for the New Drug Application for Qnexa (phentermine/topiramate) and the Prescription Drug User Fee Act (PDUFA) goal date has now been moved back from April 17 to July 17. Vivus noted that the move represents a standard extension period, but investors were a little worried and the company's stock fell 8.5% in after-hours trading to $20.98.

The review has been extended as the FDA says it needs more time to review Vivus' risk evaluation and mitigation strategy for Qnexa, which was submitted last week. The REMS is considered "a major amendment to the NDA", hence the delay.

In February, the FDA's Endocrinologic and Metabolic Drugs Advisory Committee voted 20-2 that the benefits of Qnexa outweigh the risks, a vote which suggests the Vivus drug is set to be the first prescription diet drug to reach the US market since 1999. The decision to recommend approval, after a rejection in October 2010, came with the suggestion that Vivus should conduct a post-marketing study with regards to the potential cardiovascular side effects of Qnexa.

Vivus chief executive Leland Wilson noted that the Qnexa REMS submission "is comprehensive, with materials based on ongoing feedback from the FDA since our advisory committee meeting in February". He added that "we look forward to finalising our REMS with the FDA while we move forward with our commercialisation plans".