Durect Corp. said that data from a preclinical animal test with its Chronogesic Pain Therapy Product indicate that a "small number" of units using the system experienced a stoppage in delivery of the drug.

Although that small number was said to be less than 2 percent, and the company said it is "exploring additional mechanisms" to prevent any premature shutdown, it said it expected the data to delay the restart of a Phase III program with the product that was anticipated to begin in the second half of this year.

The company's stock (NASDAQ:DRRX) fell $1.37 Friday, or 36.6 percent, to close at $2.37.

The product is an osmotic implant that delivers sufentanil, an opioid medication, continuously for three months for treating chronic pain. The drug is based on the Duros implant technology that Durect exclusively licensed from ALZA Corp., a subsidiary of Johnson & Johnson, of New Brunswick, N.J.

In August 2002, the FDA requested a delay in enrolling new patients in the Phase III trial until the clinical trial protocol was revised and approved by the FDA. The trial remains on hold, although it had anticipated restarting the trial in 2003's second half.

The company said it has not observed such an occurrence in any previous studies and remains "committed to bringing [Chronogesic] to the patients."

It has three other drug delivery technologies: the Saber Delivery System, a depot injectable used for protein delivery; Microdur Biodegradable Microparticulates, a microspheres injectable system; and the Durin Biodegradable Implant, a drug-loaded implant system.