But analysts say Glaxo is unlikely to get much share from Gilead in HIV. A dual regimen looks competitive under ideal circumstances. In the real world, even very sick patients don’t always take their medicine. This means they could become resistant to the drugs.
“We think concerns over potential for resistance emergence with real-world use will limit the adoption of this dual regimen,” RBC analyst Brian Abrahams said in a note to clients. “We do not see much incentive for physicians to prescribe dual HIV cocktails and take any chances.”
Comparing HIV Treatments
Glaxo and ViiV Healthcare tested a combination of their drugs Tivicay and Epivir, respectively, in a group of never-before-treated HIV patients. It compared that regimen to another using a two-drug combo from Gilead called Truvada plus its own Tivicay.
Tivicay plus Epivir was not inferior to the three-drug regimen at 48 weeks. None of the patients who experienced virological failure developed treatment-related resistance, Glaxo said in a news release. Virological failure occurs when the treatment doesn’t sufficiently suppress the virus.
But “key details such as the rates of virological failure, which would be important to understand how competitively this regimen behaves, were not yet disclosed,” Abrahams said. Glaxo said to expect further data at an upcoming medical conference.
From a real-world perspective, it will be important to look at patients who didn’t always take their medicine, Evercore analyst Umer Raffat said in a report.
Abrahams notes it’s in ViiV’s best interest to push a two-drug regimen. The biotech previously tested a three-medicine combination that included abacavir. Abacavir had safety issues including hypersensitivity and the potential for cardiovascular risks.
“Gilead’s triple regimens, such as Biktarvy, do not share these liabilities,” he said. “And with the advent of (Gilead’s tenofovir alafenamide), long-term renal/bone safety issues for Gilead’s regimens have been mitigated.”
Further, there have been questions regarding liver toxicity and birth defects tied to Glaxo’s drug Tivicay. This could also limit the appeal of any new regimens containing Tivicay, he said.