UPDATE 1-Achillion reports more positive data from HIV study

* Says drug was well-tolerated

* Shares up 5 percent premarket

Feb 17 (Reuters) - Achillion Pharmaceuticals Inc (ACHN.O) reported additional positive safety and efficacy data from a mid-stage trial of its experimental HIV drug, sending its shares up 5 percent.

The company's drug elvucitabine, an L-cytosine nucleoside analog reverse transcriptase inhibitor (NRTI), had earlier shown potent in vitro antiviral activity against HIV, including strains resistant to other NRTIs.

NRTI is a class of drugs for use in HIV combination therapy.

After 96 weeks of treatment, patients taking elvucitabine once daily showed a substantial anti-viral effect similar to already approved NRTI 3TC.

The drug was well-tolerated and showed a safety profile comparable to 3TC for both incidence and severity of adverse events, the company said.

Shares of the company were up 11 cents at $2.50 in premarket trade. They closed at $2.39 Tuesday on Nasdaq. (Reporting by Anand Basu in Bangalore; Editing by Aradhana Aravindna)