April 21 (Reuters) - The U.S. Food and Drug Administration has approved Merck's once-daily, oral, combination regimen for ⁠HIV infections, the drugmaker said on Tuesday, giving patients another treatment option to manage the condition.

The two-drug combination of doravirine and ⁠islatravir, branded as Idvynso, was approved to replace the current antiretroviral regimen for treating Human Immunodeficiency Virus-1 ⁠infection in some adults.

While islatravir is ‌an experimental treatment, Merck's doravirine is approved and sold in the U.S. under the brand name Pifeltro for HIV-1 treatment in combination with other antiretrovirals, and as a single-tablet regimen, Delstrigo.

HIV-1 is the most common strain of the retrovirus that causes acquired immunodeficiency syndrome, commonly known as ‌AIDS.

About 40.8 million people are living with HIV globally, and about 1.3 million ​new infections ‌occur annually, according to National Institutes of ‌Health data.

"Idvynso expands therapeutic diversity beyond the currently available oral treatment options," said Dr. Eliav Barr, senior vice president ⁠and chief medical officer, Merck Research Laboratories.

In two late-stage ‌studies with more than 1,000 ⁠patients, the treatment combination met the ​main goal of significantly suppressing replication of ‌HIV-1 in adults receiving another form of therapy.

Last year, Merck's oral drug combination was found to be non-inferior to Gilead's top-selling drug, Biktarvy, achieving similar HIV-1 suppression to the current ​standard of care.

While this is a meaningful developmental milestone for ‌Merck, ‌RBC Capital Markets analyst Trung Huynh expects initial commercial impact to be limited, with the inflection ‌point being a potential ​approval in patients who have not received any treatment.

Merck's HIV story is best viewed as a "multi-year build rather than a near-term growth driver," said Huynh.

Islatravir is being tested ⁠in multiple trials in combination with other antiretrovirals for potential daily ‌and once-weekly treatments for HIV-1.

(Reporting by Christy Santhosh and Sriparna Roy in Bengaluru; Editing by ​Sahal Muhammed, Shinjini Ganguli and Shilpi Majumdar)