Wyeth (NYSE:WYE) was on a roll with the FDA, getting three approvals in the first four months of the year, but its latest letter from the FDA didn't quite have the same happy vibe.

The drugmaker received an approvable letter for its antibiotic Tygacil as a treatment for patients with community-acquired pneumonia (CAP). Tygacil is already approved to kill the microbes causing complicated intra-abdominal infections (cIAI) and complicated skin and skin structure infections (cSSSI) in patients.

Using typical pharmaspeak, Wyeth said the FDA had a problem with the safety and efficacy of the data, but didn't really say what additional information the FDA needs, nor how long it would take to submit a response to the approvable letter.

In addition to the undisclosed issues, Wyeth said that the FDA is also worried about the liver toxicity that Tygacil may cause, and it wants more information about whether the benefits of the antibiotic outweigh the risks. Wyeth turned in what it believes is an answer to the agency's issues, but the FDA has yet to review it.

The FDA has been particularly hard on anti-infective drugs recently. Theravance (NASDAQ:THRX) had its FDA advisory committee meeting cancelled after the FDA decided it needed more time to review issues at different sites that performed its phase 3 clinical trial used to support the marketing application for its antibiotic Telavancin. Johnson & Johnson (NYSE:JNJ) also got an approvable letter for its antibiotic Ceftobiprole recently.

Johnson & Johnson has an upcoming advisory committee meeting to expand the use of Doribax into patients with hospital-acquired pneumonia. The way the FDA has been going lately, the company should probably be happy that it got Doribax approved to treat intra-abdominal infections and complicated urinary tract infections before the FDA seemingly tightened up the standards for approving antibiotics.

Given the state of the FDA, I wouldn't hold my breath while Wyeth gets things cleared up and a response resubmitted to the FDA -- it could be a while.