There’s good and bad in everything, as they say. On one hand, Wyeth should be upbeat that a low-dose, 50mg version of its Pristiq drug was effective in two late-stage trials for treating depression. On the other hand, the 100mg version, which failed to muster FDA approval earlier this year, wasn’t well tolerated in one of the Phase III studies.

You may recall that Pristiq, which is essentially a version of Effexor, is important to Wyeth’s financial fortunes. With the Effexor patent expiring in 2010, Wyeth needs a new big seller. But the drugmaker has been repeatedly frustrated by the FDA, which refused to approve Pristiq for treating depression or menopausal symptoms, partly due to manufacturing problems. The agency asked Wyeth to conduct the low-dose depression studies, which were submitted last August to the FDA, which the drugmaker now hopes will approve the low-dose Pristiq for depression in next year’s first quarter.

In earlier studies of the 100-milligram dose, a high percentage of patients complained of nausea and discontinued usage, suggesting doc wouldn’t prescribe the med or patients may not want it. So Wyeth hoped the low-dose version would cause less nausea, but still prove effective. In the latest studies, more than twice as many patients taking the 100mg dose dropped out due to side effects, such as nausea, than patients given a placebo.

Here’s the Wyeth statement.