LONDON, Aug 15 (Reuters) - A long-acting injection developed by GlaxoSmithKline and given once a month has proved as effective as standard daily pills for controlling the AIDS virus, lifting prospects for the British drugmaker's key HIV business.

GSK's majority-owned ViiV Healthcare unit said on Wednesday the experimental two-drug injection of cabotegravir and rilpivirine maintained similar rates of viral suppression compared with a standard three-drug oral regimen, after 48 weeks of a clinical trial.

The result is a boost for GSK's goal of developing two-drug HIV treatments that are easier to tolerate than conventional triple-drug therapies. If follows recent positive data from combining two oral drugs.

GSK hopes its new approach will allow it to compete more effectively against Gilead Sciences, the U.S. drugmaker that currently dominates the HIV market. (Reporting by Ben Hirschler; editing by David Evans)