Dec 19 (Reuters) - Merck's ( MRK ) experimental two-drug

combination met the main goal of significantly suppressing

replication of the HIV-1 virus in adults receiving another form

of therapy in two late-stage studies, the company said on

Thursday.

The U.S. drugmaker is seeking new growth drivers to offset a

potential hit from its blockbuster cancer immunotherapy Keytruda

losing patent protection toward the end of the decade.

Merck ( MRK ) was testing a combination of doravirine and islatravir

across the trials involving more than 1,000 patients.

In one of the studies, Merck's ( MRK ) combination was shown to be

safe and "non-inferior" to Gilead Sciences' ( GILD ) top-selling

HIV drug Biktarvy.

However, the treatment was not superior to Biktarvy in

suppressing the replication of HIV-1, the most common strain of

the virus, in the same study, which enrolled patients who were

already receiving Gilead's drug.

These patients were randomly chosen to either switch to

Merck's ( MRK ) treatment or continue on Biktarvy.

In both the studies, Merck ( MRK ) was testing its combination in

patients who were already on antiretroviral therapy, which stops

the virus from reproducing in the body.

Doravirine, branded as Pifeltro, is approved in combination

with other antiretrovirals to treat adults with HIV-1 infection

with no history of treatment failure or resistance to the drug.

It is also approved under the brand name Delstrigo as a

single, complete regimen for the treatment of these patients.

The label for doravirine carries a boxed warning, the health

regulator's strictest, to flag the risk of worsening hepatitis B

infection.

Merck's ( MRK ) combination also helped suppress viral replication

in adults compared to other antiretroviral therapy in a separate

open-label late-stage study.

The company plans to file the data with regulatory

authorities and present detailed findings at a medical meeting.