Wyeth says federal regulators have approved its new antidepressant drug.

Pristiq is the drug maker’s planned successor to its top-selling Effexor XR, Wyeth said Friday. That extended-release depression drug last year pulled in $3.8 billion.

Cheaper competition is expected to start eroding those sales as early as this summer, so a new, patent-protected replacement is crucial.

Pristiq becomes the ninth drug in two similar, widely used classes of newer antidepressants called SSRIs and SNRIs.

Madison, N.J.-based Wyeth plans to launch Pristiq by June.

Wyeth says it has several advantages over existing drugs, but analysts don’t expect it to come close to Effexor’s sales.