Pfizer said its marketed antidepressant drug candidate Pristiq® (desvenlafaxine succinate sustained-release formulation) failed a Phase III clinical trial assessing the drug’s effectiveness and safety for a new indication, major depressive disorder in children ages 7 to 17.

The pharma giant yesterday disclosed topline results that indicated Pristiq did not meet the study’s primary endpoint of demonstrating superior efficacy to placebo. Instead, Pristiq and a positive control, fluoxetine, produced results that were not statistically significant from those of placebo, Pfizer said.

In the study, a total 340 subjects were randomized into any of three treatment arms: Pristiq (weight-based dosing to achieve pediatric exposures approximating exposures in adults receiving 35 mg/day), fluoxetine (20 mg/day), and placebo. The patient population was comprised of 38.3% children ages 7–11, and 61.7% adolescents ages 12–17.

Adverse events occurring after the start of treatment in the Pristiq arm were generally consistent with those observed in both the Phase IIa pediatric MDD safety studies and the studies of Pristiq-treated adults with major depressive disorder.

The study identified no new safety signals, Pfizer said.

Pfizer said full results from the study “will be submitted for publication,” but did not detail when. The failed trial is the first of four planned clinical studies completed by Pfizer as part of an FDA post-marketing commitment under the Pediatric Research Equity Act (PREA).

Pristiq is a selective serotonin and norepinephrine reuptake inhibitor discovered and developed by Prizer predecessor Wyeth, and approved by the FDA in 2008 to treat major depressive disorder in adults.

In clinical studies, according to Pfizer, doses of 50–400 mg/day have been shown to be effective, although no additional benefit was demonstrated at doses greater than 50 mg/day and adverse events and discontinuations were more frequent at higher doses. The recommended dose for Pristiq is 50 mg once daily, with or without food.