(Reuters) - GlaxoSmithKline's prospective two-monthly two-drug injection to treat HIV was as effective as a monthly dose of the same regimen in maintaining viral suppression at 48 weeks in a late-stage study, the British drugmaker said on Thursday. The long-acting needle-based combination of its drug cabotegravir and Janssen's treatment rilpivirine met its main goal in the study, which was testing the regimen in adults with HIV-1 whose virus was suppressed.The patients were also not resistant..