A trial of a new antidepressant developed by Wyeth has found that it caused nausea, dampening expectations that it could emerge as a replacement for the company’s Effexor XR drug, which is facing the onset of generic competition later this year.

The data from the study, presented at the American Psychiatric Association meeting in Toronto, undermines Abbott’s attempt to position DVS-233 as a first-line treatment for depression, according to analysts.

DVS-233 (desvenlafaxine succinate) is a metabolite of venlafaxine, the active ingredient in both Effexor XR and its immediate-release parent Effexor. Like venlafaxine it acts as a dual serotonin/noradrenaline reuptake inhibitor, and Wyeth has said in the past that it believes desvenlafaxine has a different balance of action on these neurotransmitters which should improve efficacy and tolerability.

Effexor also has nausea as a side effect, but Wyeth will have to show that DVS-233 is significantly better than its predecessor if it is to win market share for the new product and prevent it from being labeled a ‘me-too’ drug. Added to that, DVS-233, which was submitted for approval in December 2005, will launch into an increasingly competitive market that will see nine of the 10 products leading the sector in 2004 going off patent in the 2006-2010 period.

In the Phase III trial reported at the APA meeting, around half the patients taking DVS-233 experienced nausea.

Wyeth’s Effexor franchise brought in $945 million in the first quarter of 2006, a 9% rise year-on-year, but will see its first generic competition when Teva Pharmaceutical Industries launches an authorized generic version of the drug on June 15. Wyeth will receive a percentage of the gross profit on Teva’s product, in accordance with a settlement worked out by the companies in January.

Shares in Wyeth closed down nearly 3% yesterday at $47.40.

Meanwhile, there was better news for Wyeth after it reported new clinical trial data showing that Effexor XR helped patients prevent new episodes of depression for up to two years. The results of the PREVENT study, demonstrated that patients taking Wyeth’s were significantly more likely to remain recurrence-free than patients taking placebo.