• ViiV Healthcare, an HIV drugmaker majority owned by GlaxoSmithKline, released clinical data Wednesday showing its two-drug therapy was able to keep the disease in check about as well as three-drug regimens that have similar compositions to a key competitor.
• The Phase 3 TANGO study found HIV-1 patients had similar, non-inferior rates of viral suppression after switching to ViiV’s Dovato from three-drug regimens that had an active ingredient called tenofovir alafenamide, or TAF. ViiV’s biggest rival, Gilead, notched double-digit growth in its HIV business over the past two years because of therapies that have TAF in them.
• ViiV, and GSK by extension, have been trying to wrestle away market share from Gilead by showing regimens with two drugs are as effective as those with more, but without as many side effects. Wall Street already sees Dovato as potential competition to Gilead’s biggest growth driver, Biktarvy, setting up a showdown likely to be a focal point on both companies’ second quarter earnings reports.

HIV medications have provided stability to GSK and Gilead as each works through plummeting sales of once flagship products. Yet only one company, Gilead, has been able to carve out a dominant market position. Citing data from Iqvia, Credit Suisse’s Vamil Divan last week detailed how Gilead commands 73% of the HIV drug market whereas ViiV holds 16%.

However, much of Gilead’s recent gains stemmed from a single product, Biktarvy, a mixture of TAF and two other drugs. In a note to clients, Divan wrote that while prescriptions for Gilead’s HIV drugs were up 9% year over year in the second quarter, that appears mostly due to patients switching off the big biotech’s other products and onto Biktarvy.

ViiV prescriptions, meanwhile, were down 6% for the quarter, according to Credit Suisse.

GSK and ViiV are hoping their focus on two-drug regimens will help close the gap. Though the companies got regulatory clearance for another doublet named Juluca (dolutegravir/rilpivirine) in late 2017, they expect the more recently approved Dovato (dolutegravir/lamivudine) to have greater market traction.

Dovato gained U.S. approval in April as a once-daily pill for adults with HIV-1 who hadn’t before received antiretroviral treatment and who don’t have resistances to either of the drug’s two active ingredients. Supporting that decision were two pivotal trials which pitted Dovato against a three-drug regimen of dolutegravir, emtricitabine​ and tenofovir disoproxil fumarate, or TDF.

TDF is a main component in Gilead’s older slate of HIV drugs, such as Truvada and Atripla. Now, with the positive readout from TANGO, GSK has in hand data showing that patients can successfully move off TAF-based triplets and onto Dovato.

ViiV said it will present fuller data from the trial at a medical conference later this month.