LONDON (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.

FILE PHOTO: The GlaxoSmithKline (GSK) logo. March 21, 2018. REUTERS/Loriene Perera/File Photo

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 from the big Phase III study is a boost for GSK’s goal of developing dual therapies that are easier to tolerate than conventional triple ones, and shares in GSK rose 1.5 percent. It 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 dominates the $26 billion-a-year HIV market.

Shares in Gilead, which also announced late on Tuesday that its Chief Medical Officer Andrew Cheng was leaving the company, fell 3 percent.

Gilead currently has a market share of around 52 percent against GSK’s 22 percent, but Deborah Waterhouse, who heads the British drugmaker’s HIV unit, says she hopes to overtake her U.S. rival by the mid-2020s.

That is a bold ambition, since many analysts have been expecting GSK to lose market share to Gilead’s new triple drug Biktarvy, rather than see it gain ground.

“SLOW BURN”

Liberum analyst Roger Franklin, who rates GSK a ‘buy’, believes the company’s dual-drug strategy has been under-appreciated by the market.

“Whilst duals will likely be a slow burn as resistance data is collected and the regimen gains credence among physicians, the prospects are much improved now versus a year ago,” he said.

GSK is betting that a shift to using two drugs rather than three will boost its sales by offering patients a therapy with greater convenience and fewer toxic side effects. In certain cases, depending on the drugs used, two-drug regimens will also be significantly cheaper.

Still, some doctors worry that using just two drugs to keep the AIDS virus at bay might risk drug resistance because HIV will only have to evade two drugs rather than three. That is certainly the view at Gilead, which is sticking with three.

In the case of the cabotegravir and rilpivirine monthly injection, GSK said drug resistance results in the latest study were consistent with data from earlier smaller trials. It did not go into further details but said full results would be presented at an upcoming scientific meeting.

ViiV Chief Scientific and Medical Officer John Pottage argued the novel injection offered an alternative long-term treatment for patients.

“If approved, this regimen would give people living with HIV one month between each dose of antiretroviral therapy, changing HIV treatment from 365 dosing days per year, to just 12,” he said.

Results from a second trial of cabotegravir and rilpivirine are expected later this year. Rilpivirine was developed by Johnson & Johnson and GSK is working with the U.S. drugmaker on the new injection regimen.