Competitors have stepped up efforts to market generic versions of some of Wyeth's biggest drugs, threatening to sap hundreds of millions of dollars in sales.

Teva launched a generic version of Wyeth's erosive GERD treatment Protonix  (pantoprazole) DR tablets, then ceased shipment days later after reaching a 30-day standstill agreement with Wyeth, for the purpose of negotiating a settlement. Protonix, whose compound patent doesn't expire until July 2010, had US sales of about $2.5 billion for the 12 months ended September 30, according to IMS Health.

Wyeth said it will pursue a patent infringement claim for lost profits and other damages resulting from the launch.

While Teva has not divulged the magnitude of the shipments, Robert Uhl, an analyst with Friedman, Billings, Ramsey, estimated that, between Friday and Monday when he believes the copycat versions were halted, Teva shipped $150 million worth of generic pantoprazole, whose patent was exclusively licensed to Wyeth by Altana, the firm recently acquired by Nycomed.

The FDA had approved the generic in August. In September a district court denied Wyeth's motion for a preliminary injunction that would have stopped the generic. Wyeth did not have a strong patent case, the court stated.

In another patent threat, Sun Pharmaceuticals is seeking to market an alternative formulation of Wyeth's best-selling drug, the antidepressant Effexor XR. The Indian company wants to sell a tablet version, as opposed to the currently marketed capsule form, in an effort to skirt Wyeth's patent rights. Exclusivity for the active ingredient in Effexor, venlafaxine, is set to expire in June 2008, while patent protection for the extended-release capsule formulation expires later.

Wyeth already has told Sun it won't sue for patent infringement. Total Effexor sales are on pace to exceed $3.7 billion this year, according to the Associated Press.

Meanwhile, Wyeth's efforts to bring new products to market hit another snag, as the FDA issued an approvable letter for Viviant (bazedoxifene), the second one issued this year for the pipeline drug, which Wyeth has filed for treating postmenopausal osteoporosis.

The FDA said several questions identified in its initial review of the drug were not fully resolved by Wyeth in its response to the first approvable letter, issued in April. The agency did not request any new studies, however.

Wyeth had sought to combine Viviant with estrogen in a pill for treating hot flashes, Aprela. The Viviant setback followed multiple FDA decisions to delay approval for two different versions of Effexor, for treating menopausal hot flashes and depression.