Nearly five months after its new extended-release form of amoxicillin failed in advanced human testing, sending its stock tumbling, Advancis Pharmaceutical Corp. said yesterday that it was giving the prospective drug another try.

The Germantown biotech firm's announcement came a day after its executives briefed Food and Drug Administration officials on the new strategy. Instead of giving patients the antibiotic once a day for seven days, Advancis will extend the dose to 10 days.

Testing in adults and adolescents could begin later this month, company officials said.

Advancis chief executive Edward M. Rudnic, an expert on drug dosing, said he thinks the extra three days will make the drug more effective at curing strep throat. In previous testing over seven days, the drug performed worse than standard, four-times-a-day treatment with penicillin.

"We can't be sure, but we believe that going to 10 days will provide us with that extra margin we need to have a very efficacious treatment," Rudnic said.

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

But standard amoxicillin dosing usually requires patients to take the drug precisely every six hours. The Advancis version is designed to erase that inconvenience. The firm has reconfigured amoxicillin with its proprietary Pulsys technology, which makes the drug attack bacteria in time-release, staccato bursts.

Should the new dosing work in adults, Rudnic said, the firm would likely test the new strategy in children. The seven-day dosing had also failed in children.

The question for Advancis is whether it can acquire enough momentum to regain investor confidence. Several senior executives have either left the firm or been laid off. The firm's stock, which had traded above $5 before the failures, closed yesterday at $1.41, down 3 cents.

Advancis executives said that the firm will end 2005 with about $35 million in cash and that it would have enough money to fund operations into 2007. If the test results are positive, the firm would be able to raise more money from the capital markets, said Gregory R. Wade, an analyst with Pacific Growth Equities.

"We are uncertain about the company's future if they don't achieve positive results," Wade said.

CEO Edward M. Rudnic said the extra days might make the drug more effective at curing strep throat.