Advancis Pharmaceutical Corp. said last night that its lead product, a new version of the widely used antibiotic amoxicillin, was not successful in the final round of human testing on adults.

The Germantown company was attempting to use its proprietary slow-release technology -- called PULSYS -- to allow once-a-day dosing of an antibiotic that currently must be taken several times a day.

But test results on nearly 200 adults and adolescents with strep throat showed that Advancis's version of amoxicillin was inferior to standard treatment with penicillin.

Advancis chief executive Edward M. Rudnic said last night that the company would closely evaluate the results to see what went wrong.

The firm also expects results next month from similar testing on children.

"If both trials are negative, you'd have to take a good hard look at the company's direction and strategy," Rudnic said. "Maybe this technology is not as robust as we think. But that's only if both trials are negative. I'm not willing to concede that yet."

He added, "Obviously, it's quite disappointing."

Even if the pediatric trials are successful, Advancis would have to conduct another round of testing on adults, delaying possible approval for the adult version of the drug for at least a year.

The announcement last night was another in a string of disappointments for the company.

Last October, the firm said that pharmaceutical giant GlaxoSmithKline PLC was ending a partnership to use the slow-release technology on another antibiotic, Augmentin. Advancis shares plunged 62 percent on the news.

A month later, the company laid off 19 people -- 18 percent of its staff -- and announced that it was delaying clinical trials on several other products using the technology. Advancis has said that it will have enough cash to operate through the first quarter of 2006.

The amoxicillin product is seen by investors as potentially a huge revenue generator. More than 62 million prescriptions were written for amoxicillin in 2003, and annual sales of the antibiotic total $500 million a year.

The company has scheduled a conference call at 8 a.m. today to discuss the test results with investors.

Advancis shares closed yesterday at $4.99, up 20 cents, in Nasdaq Stock Market trading.