It's a classic tale: A pharmaceutical company looks for the next big drug only to have that drug fail a late-stage trial. Then shares plummet.

That's exactly what happened to specialty pharmaceutical drug company DepoMed Inc (NASDAQ: DEPO). The company announced earlier today that Gabapentin GR, its experimental drug for nerve pain caused by shingles, failed to meet its primary goal of a late-stage trial. The primary endpoint of the Phase 3 trial was to reduce average daily pain scores, which it did, but only during the initial weeks of the treatment. After that, pain scores in patients treated with the drug were "statistically lower" in comparison with a placebo. The company also said pain relief from the medicine over the course of the study was not "statistically significant," but that the medication proved effective in reducing sleep interference.

That's gotta hurt.

Gabapentin, which is an experimental altered form of Pfizer Inc's (NYSE: PFE) Neurontin, was designed to release through gastric retention, where the drug stays in the stomach and is absorbed. Due to positive Phase 2 clinical trial data, DepoMed was counting on the drug to help it compete against Pfizer's Neurontin and its even newer treatment, Lyrica, as well as other generic drug makers who market Neurontin under the chemical name gabapentin.

Don't look for DepoMed to wave the white flag yet -- the company said it didn't expect the disappointing data to interfere with other efforts to develop Gabapentin GR as a treatment for menopausal hot flashes.

On the announcement, DepoMed shares were down a whopping 60%.