The Food and Drug Administration approved a new treatment yesterday for hospital patients with serious bacterial infections, including those resistant to most other antibiotics.

The new drug, called Tygacil, is from the first new class of antibiotics to be marketed in several years. The manufacturer, Wyeth Pharmaceuticals, said the intravenous drug will be used as a first-line treatment for stomach and skin infections and is effective against enough different bacteria to be used before doctors know which ones are causing the infection.

"Community and hospital-acquired infections have the real potential to become a major public health crisis," said Evan Loh, a Wyeth vice president. "The need for more antibiotics is acute."

The announcement was welcomed by doctors, especially those who are regularly confronted with bacterial infections that are resistant to existing antibiotics.

"It's very difficult to know how to treat and manage badly infected patients today," said Scott R. Schell, a professor of surgery at the Cancer Institute of New Jersey. "For the worst infections and sickest patients there are few options, so any new treatment is very appreciated."

The Centers for Disease Control and Prevention estimates that every year 2 million Americans acquire infections while in hospitals, and 90,000 die. About 70 percent of the hospital infections are resistant to at least one class of antibiotics.

The new drug is from a class of medicines called glycylcyclines, which is related to the tetracycline class. The two are different enough, however, that Tygacil can be used to treat infections that are resistant to tetracycline, said Janice Soreth, director of the FDA's division of anti-infective drugs.

Soreth also said the approval marked an important advance because "it's another option, another choice out there, and there are a limited number of options."

Developing new antibiotics is time-consuming and expensive, and drug companies have been slow to come up with new types in recent years. Wyeth officials said yesterday that the molecule that became Tygacil was first synthesized in 1992, and clinical development began in 1997.

"Few broad-spectrum antibiotic agents are currently in development," the company said in a statement. "Antibiotic development has slowed to the point that FDA has had few opportunities to approve new agents. In fact, development and approvals of new antibacterial agents have decreased by 56 percent over the past 20 years."

Although new antibiotics have been few and far between, the use of existing drugs has grown markedly in both human medicine and to treat and promote the growth of farm animals. Because bacteria will eventually grow resistant to any antibiotic they encounter frequently, the pool of resistant bacteria is expanding fast.

Schell, who spoke on a Wyeth teleconference but said he had no relationship to the company, said Tygacil is especially welcome because it can defeat a number of broadly resistant bacteria such as methicillin-resistant Staphylococcus aureus, and because it is effective against a wide range of bugs, including E. coli.

"It's important to get the right antibiotic because if you don't choose right the first time, the patient does poorly," he said. It can take one to two days of laboratory work to determine exactly what bacteria is causing an infection.

The company said it is exploring other uses for the drug, including fighting pneumonia and some pediatric infections.