Is Merck’s HIV Win Really About Keytruda?

When Merck & Co. (NYSE:MRK) reported Phase 3 data showing its two-drug HIV regimen of doravirine and islatravir matched the efficacy of Gilead Sciences’ Biktarvy, it wasn’t just another clinical headline. It was a strategic signal. The study showed non-inferiority at 48 weeks in treatment-naïve adults with HIV-1, with a similar safety profile. In plain English, Merck proved a two-drug pill can stand shoulder to shoulder with the world’s best-selling three-drug HIV therapy. That matters on its own. But it matters even more because Keytruda, Merck’s cancer powerhouse, faces U.S. patent expiry starting in 2028. Management has been vocal about building “green shoots” beyond oncology. This HIV data is one of the clearest examples yet. Investors aren’t just looking for science wins. They’re looking for durable revenue engines that can soften the Keytruda patent cliff. This one checks more than a few boxes.

Clinical Non-Inferiority Vs Biktarvy

The headline result was straightforward: doravirine/islatravir achieved non-inferiority versus Biktarvy at 48 weeks. That’s not trivial. Biktarvy is widely considered the gold standard in first-line HIV treatment. It combines three drugs and has built a reputation for potency and tolerability.

Merck’s regimen uses two drugs instead of three. Both target reverse transcriptase, but through different mechanisms. Doravirine is a non-nucleoside reverse transcriptase inhibitor. Islatravir is a nucleoside reverse transcriptase translocation inhibitor. It is highly potent and dosed at just 0.25 milligrams per pill.

In HIV, simplicity matters. Fewer drugs can mean fewer long-term toxicities and drug-drug interactions. Physicians often rotate patients over time. That creates room for differentiated options. A two-drug regimen without an integrase inhibitor also stands apart from most modern first-line therapies.

Importantly, Merck showed similar safety to Biktarvy. That reduces one major adoption hurdle. The company is positioning islatravir as a new anchor compound. If it works across multiple combinations, the platform potential expands beyond one pill.

Strategically, this isn’t about dethroning Biktarvy overnight. It’s about proving parity. In a mature market, matching the leader opens doors. From there, commercial execution does the rest.

Regulatory Visibility & Timeline

Clinical data gets attention. Regulatory milestones move stocks. Merck has already filed a new drug application for doravirine/islatravir. The FDA is reviewing it, and management has described the process as routine so far.

There is a clear PDUFA date in view. That reduces uncertainty. Investors often discount pipeline assets heavily until approval looks tangible. A defined timeline changes that math. It allows analysts to start modeling revenue with more confidence.

Merck also has broader regulatory momentum. The company has emphasized that ten major programs could be substantially derisked by the end of 2027. Doravirine/islatravir sits within that near-term window. That timing matters because it overlaps with the ramp-up period before Keytruda faces biosimilar pressure.

Regulatory clarity also helps with capital allocation. Merck has been active in business development, including the Cidara and Verona deals. But internally developed assets carry higher long-term margins. An approved HIV regimen built on proprietary science strengthens operating leverage.

There is still risk. FDA reviews can surprise. Label language will matter. But compared with early-stage programs, this one has crossed the most important hurdle: Phase 3 success. The remaining path is visible.

HIV Pipeline Breadth & Differentiation

The two-drug daily pill is only part of the story. Merck’s HIV pipeline now includes once-weekly oral regimens and even a once-monthly oral prevention candidate. That breadth is intentional.

The company is collaborating with Gilead Sciences on islatravir plus lenacapavir as a potential once-weekly oral treatment. If successful, it could be the first of its kind. There is currently no weekly oral two- or three-drug regimen on the market.

Weekly dosing could appeal to patients seeking flexibility. It may also help differentiate in a crowded space dominated by daily pills and long-acting injectables. Merck is betting that optionality drives share.

Islatravir is the common thread. Management views it as a next-generation nucleoside with high potency and resistance barrier. If it anchors multiple regimens, the commercial runway extends well beyond one product cycle.

Competition remains fierce. Gilead continues to innovate. Long-acting injectables from other players are gaining traction. But Merck is not chasing a single niche. It is building a portfolio approach within HIV.

From a financial lens, diversification within one therapeutic area can smooth revenue volatility. Instead of relying on a single blockbuster, Merck could layer multiple mid-to-large products over time.

Strategic Hedge Against Keytruda LOE

All of this circles back to Keytruda. The drug generated $8.4 billion in fourth-quarter sales alone. It remains the backbone of Merck’s growth. But core U.S. patents begin expiring in 2028, with additional method patents extending into 2029.

Management has been conservative in planning. They assume 2028 for modeling purposes. That’s prudent. It also means the clock is ticking.

Merck has outlined a $70 billion non-risk-adjusted commercial opportunity by the mid-2030s. That figure more than doubles consensus peak Keytruda revenue estimates. HIV is one component of that broader transformation.

An approved, competitive HIV regimen could generate meaningful multibillion-dollar sales over time. It won’t replace Keytruda on its own. Few drugs could. But it can contribute to a mosaic of growth drivers.

Importantly, HIV revenues would be less exposed to oncology-specific pricing pressures and IRA dynamics. That diversification matters. Investors often discount companies heavily when a single product dominates profits.

The market is already reassessing Merck’s valuation. As of late February 2026, shares trade around 5.2x LTM enterprise value to revenue and roughly 11.8x LTM EV/EBITDA. LTM price-to-earnings sits near 16.8x. Those multiples have expanded from prior quarters, reflecting renewed confidence but not exuberance.

If pipeline execution continues, the valuation could stabilize. If setbacks emerge, the reliance on Keytruda will again take center stage.

Final Thoughts

Merck’s Phase 3 win in HIV is not a silver bullet. It does not erase Keytruda’s looming patent expiry. It does not guarantee blockbuster sales. But it shifts the narrative from dependence to diversification.

Clinically, matching Biktarvy with a two-drug regimen is meaningful. Regulators are already reviewing the filing, which reduces timing uncertainty. The broader HIV pipeline adds optionality, especially with weekly dosing in development.

Financially, the story is about risk mitigation. Merck is assembling multiple assets to soften the Keytruda cliff rather than searching for one miracle successor. That approach can create steadier growth, even if no single drug replicates Keytruda’s scale.

At roughly 11.8x LTM EV/EBITDA and 16.8x LTM earnings, the stock does not look stretched relative to large-cap pharma peers. It also no longer trades at the depressed multiples seen during peak patent anxiety. The valuation reflects cautious optimism.

For investors, the takeaway is balanced. The HIV data strengthens Merck’s strategic position. Execution over the next two years will determine how much of that potential turns into durable revenue.

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