NEW YORK (AP) -- Impax Laboratories said Tuesday that it will develop and market Durect's Eladur patch, which is designed to treat pain associated with the viral infection shingles.

Impax said it will pay Durect $2 million upfront, and the company will could make $61 million in additional payments based on development and sales targets. Durect will also receive royalty payments if Eladur is approved.

Impax Laboratories Inc. said it will control and fund development of Eladur.

Durect Corp. has long been developing Eladur as a treatment for pain associated with post-herpetic neuralgia, or pain that follows shingles. The drug succeeded in some early studies but missed its primary goal in a midstage clinical trial in 2011. At the time Durect was developing the product through a partnership with King Pharmaceuticals, which is now a unit of Pfizer Inc.

Shares of Impax slipped 18 cents to $25.04 in morning trading. Durect shares added 8 cents, or 4.2 percent, to $1.86 and reached a two-year high of $1.88.