Heck, if your drug doesn't work, then blame Eastern Europe. That's what biotech firm

Cubist Pharmaceuticals


did Wednesday after it warned of failing results from a late-stage test of its experimental antibiotic Cidecin.

Cubist is testing Cidecin as a treatment for serious pneumonia, but in a late-stage test that compared it with an existing treatment, the drug failed to show superior efficacy, the company said.

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But Cubist believes that geography is at least partly to blame for the bad test result. The biotech said Cidecin proved effective in North American and Western European patients, but ineffective in Eastern European and South African patients. Cubist's statement did not explain precisely why it thought location mattered to the test.

Unfortunately for Cubist, it's the global results that count, so the Cidecin trial was a bust.

Shares of Cubist plunged more than 50% to $16.09 per share in Wednesday after-hours trading. The stock closed the regular session down 34 cents to $31.75 per share.

Cubist said it is suspending patient enrollment in a second, late-stage Cidecin pneumonia trial until it can further review the results from the first test. The company said one option it is exploring is to restrict patient testing to North America and Western Europe.

Cidecin has proven to be an effective antibiotic for the treatment of complicated skin and soft-tissue infection, based on results from two late-stage clinical trials. Cubist's original plan was to seek Cidecin approval from the Food and Drug Administration for both diseases in the third quarter. But given problems with the pneumonia trials, the company may now just file for approval for skin infections.