What happened

Shares of SAGE Therapeutics Inc. (NASDAQ:SAGE) are rocketing higher today in response to positive clinical trial data for a postpartum depression candidate. Investors are pushing up Marinus Pharmaceuticals Inc. (NASDAQ:MRNS) stock in hope that a similar candidate will succeed in an ongoing study as well. As of 10:50 a.m. EST, Sage and Marinus have risen 50.2% and 16.8%, respectively.

So what 

In September, after brexanolone failed to show a significant benefit for patients who suffer persistent seizures, enthusiasm for the drug sank. That loss gave the stock extra room to run following today's announcement that brexanolone hit its main goals in a phase 3 trial designed to support applications for the treatment of moderate and severe postpartum depression (PPD).

Excited person with arms raised in front of an upward sloping chart.

Image Source: Getty Images.

Marinus Pharmaceuticals Inc.'s lead candidate, ganaxolone, acts on the same target in the brain as brexanolone. Although Marinus has designated severe forms of epilepsy as ganaxolone's lead indication, it's also running a phase 2 PPD trial with its candidate.

Now what

Marinus intends to begin a phase 3 trial for ganaxolone as a treatment for a rare form of epilepsy sometime next year. A phase 2 study with the candidate as a treatment for severe PPD is currently enrolling patients, and an ongoing study with moderately affected mothers should throw off some data in 2018.

As for Sage Therapeutics and its candidate, investors will want to keep an eye open for several possible signs of trouble with brexanolone. Investigators like to see a drug's efficacy increase along with the dosage, but severely affected patients in the lower dosage group showed a stronger improvement than those receiving a higher dosage.

While PPD represents an enormous unmet need, predicting brexanolone's potential in this indication is trickier than predicting how many times a newborn baby's going to wake you up each night. The condition often goes undiagnosed, and Sage's candidate isn't an easy-to-swallow pill patients can take on their own. Instead, it's an intravenous infusion that takes 60 hours to complete.

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