New antibiotics are urgently needed, as bacteria evolve to resist treatment by today's drugs.

Tygacil is the first in a new class of antibiotics, derived from the older tetracycline family, said Dr. Edward Cox of the Food and Drug Administration. It is made by a unit of the drugmaker Wyeth, based in Madison, N.J.

First-Line Therapy

It is a broad-spectrum antibiotic, meaning it can fight a range of bacteria, including the worrisome germ called methicillin-resistant staph aureus, or MRSA. Once spread mostly in hospitals, this hard-to-treat bacterium now is increasingly spread in the community as well, such as between athletes.

"Certainly having additional therapeutic options available is beneficial," Cox said.

Maker Wyeth Pharmaceuticals said Tygacil can be used as first-line therapy, and in studies proved comparable to some two-drug combination therapies now in use.

Warnings Similar to Tetracyclines

The most common side effects are nausea and vomiting. But Cox said Tygacil comes with additional warnings similar to tetracyclines: It's not for use in pregnant women, and may discolor the teeth if given to young children. Wyeth said it should be administered with caution in patients allergic to tetracyclines.

Wyeth shares rose 31 cents to close at $43.50 on the New York Stock Exchange. Its shares have traded in a 52-week range of $33.50 to $45.67.