Opexa Therapeutics Inc said on Tuesday further analysis of clinical data shows that more than 83 percent of patients taking its experimental multiple sclerosis drug remained relapse-free after a year, more than doubling the value of the company's shares.

The biotechnology company said the favorable data were seen in a mid-stage study of 150 patients with relapsing remitting multiple sclerosis. Patients with this type of MS -- typically the initial stage of the progressive neurological disease -- have unpredictable relapses followed by months to years of no new signs of disease activity.

The company said the annualized relapse rate among patients who took its Tovaxin drug fell to 20 percent, a 42 percent reduction compared to placebo.

Shares of Opexa, which is based in The Woodlands, Texas, were up $1.67 to $3.20 in heavy morning trading on the Nasdaq. (Reporting by Ransdell Pierson, editing by Dave Zimmerman)