The US Food and Drug Administration has told Wyeth that it must sort out quality control at one of its manufacturing plants if it is to receive approval for its new antidepressant Pristiq.

The agency has issued an approvable letter for Pristiq (desvenlafaxine), saying that a satisfactory inspection of the company's Guayama, Puerto Rico facility, which is where the drug will be manufactured, is needed before the green light can be given.

Wyeth will also have to take on “several post-marketing commitments,” including submission of long-term relapse prevention, low dose and pediatric studies, and must provide “additional clarity” around its product education plan for physicians and patients. The good news for the firm is that the FDA does not require that any additional clinical studies be submitted prior to the approval of Pristiq, which is the follow-up to Wyeth’s antidepressant blockbuster Effexor (venlafaxine).

"The approvable letter is in line with Wyeth's expectations and we remain on track with our plans for Pristiq," said senior excutive Joseph Mahady, who added that “we are working toward resolution of all outstanding issues at our manufacturing site in Guayama." The launch of Pristiq also depends on the progress of an FDA review of Wyeth's separate New Drug Application for vasomotor symptoms associated with menopause. Wyeth is also trying out a low-dose 50 mg version of Pristiq in the hope that it will be better tolerated than doses of up to 400mg used in earlier studies, thus reducing the drug's tendency to cause nausea.

Pristiq is expected to have annual sales of more than $1 billion, which will compensate for the loss of earnings once the extended-release version of Effexor faces generic competition in 2010.

Third Prempro trial begins

Meantime, a trial has started in Arkansas where a woman, Helene Rush, is alleging that Wyeth’s hormone-replacement therapy Prempro (conjugated estrogens/medroxyprogesterone acetate) caused her breast cancer, the third time a case involving the drug has gone to trial. 5,000 similar lawsuits have been filed across the USA.

In the first trial, a jury last year rejected claims made against Wyeth by another Arkansas woman, while in the second case, a married couple won a $1.5 million award against Wyeth, but the judge declared a mistrial for undisclosed reasons. The company denies any negligence and has previously said that it has informed patients of the risks, as well as the benefits, of taking Prempro.