Versicor Inc. began a pair of Phase III trials on its leading antibiotic product candidate, dalbavancin, to treat skin and soft-tissue infections.

Dalbavancin is being developed as the first once-a-week, injectable, hospital-based antibiotic for Staphylococcal (Staph) and other serious Gram-positive infections. The Fremont, Calif.-based company said it expects to conclude the trials in the first half of 2004.

Each of the two randomized, double-blind studies will evaluate in about 550 hospitalized patients the safety and efficacy of dalbavancin vs. current standard antibiotics.

In the first trial, patients with complicated skin and soft-tissue infections will receive either a 1-gram intravenous dose of dalbavancin on the first day followed by a 500-mg dose on the eighth day, or approved doses of linezolid for 14 days.

In the second study, patients with uncomplicated skin and soft-tissue infections will receive either a 1-gram intravenous dose of dalbavancin on the first day, with the option of adding a 500-mg dose on the eighth day, or intravenous cefazolin, followed by oral cephalexin. On day eight, the investigator will decide the duration of study medication therapy (seven or 14 days) based on the patient's status.

In addition to studying dalbavancin's once-weekly regimen, the trials also will evaluate the drug's ability to treat methicillin-resistant Staph infections.

"Over the last five to 10 years we've seen an increasing prevalence of methicillin-resistant Staph aureus and methicillin-resistant Staph epidermidis," Versicor Chief Financial Officer Dov Goldstein told BioWorld Today. "So now doctors are forced to treat presumptively when they're worried about Staph as if it was a methicillin-resistant organism. This is where 90 percent of vancomycin is used."

Dalbavancin, a next-generation glycopeptide agent that belongs to the same class as vancomycin, was designed as an improved alternative to vancomycin.

"Our drug is exquisitely potent against both of these organisms, substantially more potent than vancomycin and a number of other agents being used," Goldstein said. "It's reliably bactericidal against both these pathogens and other Gram-positive organisms."

Previously reported Phase II results showed that once-weekly dalbavancin produced higher clinical and microbiological response rates than a variety of standard-care regimens, including vancomycin, and also was well tolerated.

Dalbavancin's potency, tissue penetration and long half-life allow for more flexible dosing regimens than those used for current standards. Long-term treatment courses could take advantage of a more convenient dosing schedule, possibly avoiding at-home intravenous dosage or hospital stays requiring 14 to 21 doses per week of vancomycin. But the once-weekly treatment also could prove to be more than convenient - in reducing a need for IV lines in some patients, dalbavancin's dosing schedule could potentially reduce local and bloodstream infections and result in shorter hospital stays.

"This creates a huge advantage in the marketplace in a couple of settings," Goldstein said.

Another Phase II trial is under way, studying dalbavancin's ability to treat catheter-related bloodstream infections resulting from Gram-positive organisms.

Versicor is developing dalbavancin for U.S. and Canadian commercialization under a licensing agreement with Biosearch Italia SpA, which owns the compound's rights in the rest of the world. But a proposed merger, in which Versicor would pay $260.7 million in stock for Milan, Italy-based Biosearch, would consolidate all rights. The merger is expected to close early next year. (See BioWorld Today, Aug, 1, 2002.)

"This merger gives us a larger amount of territory - we'll sell now directly into Europe as well as the U.S. - and increases the margins on the product," Goldstein said.

Versicor's stock (NASDAQ:VERS) fell 29 cents Tuesday to close at $10.09.