It wasn't the answer Theravance (NASDAQ:THRX) hoped for, but at least it came on time. The last time the company got a complete response letter from the Food and Drug Administration, it had to wait seven months after its PDUFA date for the rejection.

Friday's newest complete response letter applies to Theravance's antibiotic Vibativ, which it's trying to get approved for treating patients with nosocomial pneumonia -- a fancy name for pneumonia acquired while in a hospital.

The clinical trials measured how well the antibiotic was able to get rid of the pneumonia as a primary endpoint, with survival as a secondary endpoint. According to Theravance, the former is what the current draft FDA guidelines for antibacterial clinical trials in nosocomial pneumonia ask for.  

But the FDA appears to be moving the goalposts. It now wants more data and analysis on the survival aspect, to bump it up to a primary endpoint. Fortunately, Theravance saw the change coming and has already collected and analyzed the data.

It seems to be getting harder and harder to get antibiotics on the market these days. Wyeth's Tygacil, now owned by Pfizer (NYSE:PFE), two antibiotics from Johnson & Johnson (NYSE:JNJ) -- Doribax and ceftobiprole -- and even Vibativ on its original approval, have all been turned down for FDA approvals in recent years. The only companies that look like they'll have an easier time getting antibiotics on the market are generic-drug makers. The FDA is likely to follow an advisory committee recommendation to approve generic versions of Viropharma's (NASDAQ:VPHM) Vancocin.

Vibativ is already approved to treat complicated skin and skin-structure infections -- delightful! -- and was launched with help from its marketing partner Astellas earlier this month. The lack of a new approval won't affect that indication, but will keep Theravance and Astellas from marketing it for use in pneumonia patients.

Theravance plans to submit the updated data in the next month or two. Hopefully, investors won't get bedsores waiting for another decision from the FDA.