MRK — Merck: The Keytruda Cliff Has Its First Bridge

The FDA approved Merck's Lipfendra (enlicitide) on July 16 — the first oral PCSK9 inhibitor ever, confirmed by both the FDA's own press release and Merck's announcement. This is the first concrete pipeline asset that could materially offset the Keytruda biosimilar cliff starting in 2028. Keytruda generated $31.7B in FY2025 — 49% of Merck's total revenue — and the market has been pricing MRK at a discount to pharma peers because no successor asset had proven it could scale. Lipfendra changes that question, even if it doesn't fully answer it.

The Call: ACCUMULATE

Accumulate on weakness below $125. You are buying a company at ~18× annualized earnings (Q1'26 diluted EPS of $1.72 × 4 = $6.88, vs. price ~$124.4) with the first genuine pipeline diversification catalyst since the Keytruda cliff became the thesis. The upside is not "Lipfendra replaces Keytruda" — it's that Lipfendra plus Winrevair plus the broader pipeline narrows the gap enough that the discount-to-peers multiple rerates.

Why Now

Three things make this live this week. First, the FDA approval is fresh — July 16, five days ago — and the sell-side is still calibrating peak sales estimates. Scotiabank's Louise Chen put peak potential at "tens of billions of dollars"; Pienomial modelled $5B by 2034. That range is wide enough that any initial prescription data or formulary placement news will move the stock. Second, Merck reports Q2 2026 earnings in late July — Keytruda's growth trajectory in the last full year before the cliff matters for the base case. Third, MRK at $124.4 with $6.88 annualized EPS and $3.92B quarterly operating cash flow is not expensive for a pharma with this pipeline.

The Evidence

Q1 2026 (10-Q, filed 2026-05-04, period ending 2026-03-31):

Keytruda concentration (FY2025, per BioSpace): - Keytruda revenue: $31.7B = 49% of total revenue - Keytruda patent expiry: 2028 (biosimilars enter)

Lipfendra (FDA approved July 16, 2026): - First oral PCSK9 inhibitor (confirmed by FDA.gov and Merck press release) - List price: $315/month ($10.50/day) - Existing PCSK9 injectables (Repatha at $239/month, Praluent) had slow adoption due to cost and payer access - Peak sales estimates: $5B (Pienomial, 2034) to "tens of billions" (Scotibank)

At ~$124.4, MRK trades at ~18.1× annualized P/E. For a company generating ~$15.7B in annualized operating cash flow with a $307B market cap, that's a ~19.6× OCF multiple — not cheap, but defensible for a pharma with a diversified post-cliff pipeline.

Levels & Triggers

• Entry zone: Accumulate below $125. The P/E is reasonable and the pipeline narrative is improving.
• Upside trigger: Early prescription data showing Lipfendra uptake outpacing Repatha's early trajectory. A clean Q2 print with Keytruda still growing double digits confirms the base case. Winrevair (sotatercept) revenue acceleration in Q2 would add a second growth leg.
• Kill the thesis: PCSK9 oral uptake mirrors the injectable disappointment — payer formulary exclusion or prior-auth hurdles suppress prescriptions. Or: Q2 shows Keytruda growth decelerating below 5% YoY, signalling the cliff is arriving early.

Horizon

12-24 months. The Lipfendra launch curve and Keytruda's growth rate through 2026 and 2027 determine whether MRK re-rates toward pharma peers (20-22× P/E) or stays in the cliff-discount band (16-18×).

The Bear Case — Argued Honestly

PCSK9 inhibitors have failed commercially before. Repatha and Praluent were supposed to be blockbusters; both underperformed because payers demanded prior authorization, step therapy through statins, and documentation of familial hypercholesterolemia. Lipfendra is oral, which helps adherence and convenience, but $315/month is more expensive than Repatha's $239/month cash price. If payers apply the same access restrictions — and there is no reason to think they won't — Lipfendra's peak sales will land closer to $1-2B than $5-10B, and the Keytruda cliff remains uncovered. The "tens of billions" estimate is a best-case scenario that requires broad formulary access and outcomes data that does not yet exist (Pienomial flags a "critical cardiovascular outcomes data gap"). Without outcomes data, Lipfendra is a lipid-lowering drug, not a mortality-reducing drug — and payers treat those differently.

What I'm Watching

1. Q2 2026 earnings (late July): Keytruda YoY growth rate and Winrevair revenue trajectory — these determine the base case under the cliff.
2. Lipfendra formulary placement: Watch Express Scripts, CVS Caremark, and OptumRx formulary decisions in August-September. Broad coverage at Tier 2 changes the peak sales math.
3. Cardiovascular outcomes trial: Merck needs a morbidity/mortality trial (not just LDL reduction) to unlock broad payer access. Timing of that readout is the single biggest variable.

This issue re-underwrites Merck based on internal research dated July 17, 2026, updated with FDA approval confirmation (July 16, 2026), SEC financials (Q1 2026 10-Q), and current market data. Financials are as of 2026-03-31; market data as of 2026-07-21; Keytruda FY2025 revenue per BioSpace.

Sources

• FDA — Lipfendra approval announcement — July 16, 2026
• Merck — Lipfendra press release — July 16, 2026
• SEC EDGAR — Merck 10-Q (Q1 2026) — filed 2026-05-04
• BioSpace — Keytruda $31.7B FY2025 — FY2025 revenue
• Pienomial — Lipfendra $5B peak sales by 2034 — 2026
• FiercePharma — Lipfendra first oral PCSK9 — July 2026
• Merck Investor Relations — company IR page

Axelrod Research is independent equity analysis. This is for information only, not investment advice. No personalized recommendations. Figures are sourced and dated; verify before acting.