Endo Pharmaceuticals dropped out as SkyePharma plc's North American development partner for Propofol IDD-D, leaving the future of the anesthetic in limbo as the London-based company decides the next steps.

While no clear reason was given as to why Chadds Ford, Pa.-based Endo and SkyePharma agreed to terminate the program, development of Propofol IDD-D appeared to be at a standstill for at least the last two years.

In April 2004, it had completed a Phase II trial that provided evidence of efficacy and safety in 79 female patients undergoing laparascopic gynecological surgery. The product was expected to enter Phase III trials later that year but never did.

A spokesman from Endo referred all questions to the company's quarterly news release, which came out Thursday and stated "recent data have indicated that the product has a low likelihood of being able to achieve the agreed-upon targeted product profile."

SkyePharma's London headquarters referred all questions to the San Diego office, which handles the development of Propofol IDD-D, but officials there could not be reached Friday. The company's press release said it is "evaluating its options worldwide," and that the product "remains under strategic review."

SkyePharma and Endo entered their agreement for Propofol IDD-D in December 2002.

The collaboration required SkyePharma to cover the costs of Phase III development, which was estimated to be up to $30 million, but the company also expected to receive up to $45 million in additional milestone payments if Propofol IDD-D was approved by the FDA with a label meeting certain predetermined criteria. The deal included a share of between 30 percent and 60 percent of Endo's sales, money that SkyePharma would have used to pay for manufacturing costs.

The agreement also gave Endo North American rights to DepoDur, formerly called DepoMorphine, which received FDA approval in May 2004 to treat pain following major surgery. That partnership is not affected by the terminated joint development of Propofol IDD-D. A single-dose, sustained-release, injectable formulation of morphine, DepoDur was launched in early 2005 and Endo reported sales of $900,000 in the first quarter of this year.

Endo has invested a significant amount of money in its partnership with SkyePharma. In addition to a $25 million up-front payment when the original agreement was signed in 2002, SkyePharma received a $5 million milestone payment in April 2004 for completing the Phase II trial of Propofol IDD-D, and another $5 million from Endo the following October related to DepoDur, which was launched a few months later.

Propofol is supplied as a 1 percent injectable emulsion and is used for induction of short-term anesthesia of between 30 minutes and 60 minutes, or as an infusion for sedation.

Propofol IDD-D is a 2 percent intravenous formulation of propofol that employs SkyePharma's Insoluble Drug Delivery technology and is designed to avoid the need for a preservative to prevent microbial contamination.