December 2028
Keytruda primary US compound patent expires
No US biosimilar filing has been announced; Samsung Bioepis has filed in Korea.
When does Keytruda go off patent?
In the US, biosimilars can launch from 2028. Keytruda is sold by Merck. Primary US compound patent expires December 2028. Includes subcutaneous Keytruda Qlex. EU exclusivity to 2031.
Keytruda's US exclusivity date is based on company guidance. The date comes from the company's own filings or guidance. Secondary patents, new formulations or litigation can still move it. It is a biologic, so copies are biosimilars. Biosimilars are harder to make and usually erode sales more gradually than generics.
| Patent or protection | Covers | Expiry |
|---|---|---|
| Primary US compound patent | Pembrolizumab itself | December 2028 |
| Two more patents in the compound family | Pembrolizumab itself (extended for patent office delay) | November 2029 |
| EU compound patent | Pembrolizumab itself (Europe) | 2031 |
| Keytruda Qlex patents | The under-the-skin version (pembrolizumab with berahyaluronidase alfa) | 2043 |
Merck expects biosimilars could begin in December 2028, when the primary compound patent expires. Two more patents in the same family run to May and November 2029, but Merck expects them to be challenged in court. Europe follows in 2031 and Japan in 2032 to 2033. Keytruda Qlex, the under-the-skin version approved in 2025, has patents to 2043, so moving patients to it is Merck's main defence. Halozyme says Qlex infringes its patents on the enzyme used to deliver it: it sued Merck in New Jersey in 2025, and in October 2026 a Dutch court barred the under-the-skin version in eight European markets. Merck calls the patent invalid. The IV version is not affected.
Sources: Merck 10-K 2025 · Fierce Pharma: Halozyme ruling
| Year | Worldwide | US | Growth |
|---|---|---|---|
| 2023 | $25.01B | $15.11B | – |
| 2024 | $29.48B | $17.87B | +18% |
| 2025 | $31.68B | $18.87B | +7% |
Worldwide net sales as reported, with the US share. Source: Merck 10-K 2025 (Keytruda plus Keytruda Qlex)
Filed with the FDA In October 2026 the FDA accepted Formycon and Zydus's application for FYB206, the first publicly announced Keytruda biosimilar under US review, with a decision expected in Q3 2027. Formycon skipped a comparative Phase 3 trial on a path agreed with the FDA. Samsung Bioepis has reported Phase 3 results and filed in Korea.
| Company (product) | Stage |
|---|---|
| Samsung Bioepis (SB27) | In clinical trials. Phase 3 complete; filed in Korea, Aug 2026 |
| Celltrion (CT-P51) | In clinical trials. Phase 3; filed in Korea |
| Formycon / Zydus (FYB206) | Filed with the FDA 2026. FDA accepted the application for review in Oct 2026; decision expected Q3 2027 |
| Amgen | In clinical trials |
| Sandoz | In clinical trials |
| Henlius | In clinical trials |
| mAbxience | In clinical trials |
| BioNTech | In clinical trials |
| Qilu / Cipla | Stage not disclosed. US partnership signed, Sep 2026 |
| Alvotech / Dr. Reddy's (AVT32) | In clinical trials. US filing planned for 2028 |
Checked October 2026. Sources: Formycon and Zydus: FDA accepts FYB206 · Pearce IP: Samsung Bioepis Korea filing · Pearce IP: pembrolizumab trials update · Pearce IP: Cipla and Qilu · ClinicalTrials.gov: AVT32
Among past biologics facing biosimilars, US sales in the first full year after copies arrived were a median 65% of the last full year before (range 34% to 93%, 7 drugs), and 27% by the third year (9 drugs). Biosimilars usually take share more gradually than generics. Every drug is different: settlements, how many copies launch, and pricing all change the curve. See the erosion benchmarks →
| Scenario | 2025 US sales | Year 1 (about 2029) | Year 2 | Year 3 |
|---|---|---|---|---|
| Fastest past case | $18.9B | $6.41B34% | $2.01B11% | $0.81B4% |
| Median | $18.9B | $12.3B65% | $7.24B38% | $5.01B27% |
| Slowest past case | $18.9B | $17.6B93% | $14.3B76% | $12.0B64% |
An illustration, not a forecast: it applies the past-cliff benchmarks to Keytruda's 2025 US sales, held flat until copies arrive in 2028. Year 1 is the first full year with copies on sale.
Keytruda is 49% of Merck's 2025 revenue ($31.7B of $65.0B). With Januvia, Lynparza and Gardasil, the drugs tracked here add up to 63% of Merck's revenue losing US exclusivity by 2028.
Bars show each company's tracked drugs as a share of its total 2025 revenue. Keytruda is highlighted.
No US biosimilar filing has been announced; Samsung Bioepis has filed in Korea.
Formycon and Zydus's FYB206 is the first publicly announced Keytruda biosimilar under FDA review; a decision is expected in Q3 2027. Merck's primary US compound patent expires in December 2028. Formycon and Zydus