Halozyme has stalled the launch of Merck's subcutaneous formulation of Keytruda in select European countries, filing patent claims that the U.S. drugmaker says it will contest, Fierce Pharma reports.

The dispute centers on the delivery technology behind the injectable version of Keytruda, Merck's top-selling cancer immunotherapy. Halozyme's patent assertions have effectively put the brakes on the product's introduction in certain European markets, where Merck had planned to convert patients from the long-standing intravenous formulation.

Merck has publicly committed to defending the launches. The company vows to fight the patent claims rather than accept a delayed rollout, setting the stage for litigation across multiple European jurisdictions.

What does the dispute mean for the parties?

For Halozyme, the patent claims protect its interests in the technology underpinning subcutaneous drug delivery, a field where the company has built a substantial licensing business. Blocking an unauthorized launch preserves both its revenue position and its negotiating leverage.

For Merck, the stakes are commercial and strategic. Subcutaneous Keytruda offers patients a far shorter administration time than the intravenous version, and a broad European launch is central to the franchise's next phase. Any country-by-country delay fragments that rollout.

What happens next?

Expect parallel patent proceedings in the affected European countries, with outcomes likely to vary by jurisdiction and by the specific patents asserted. Merck's stated willingness to fight signals litigation rather than a quick settlement.

Practitioners advising in the pharma space will watch whether Halozyme's claims survive validity challenges — and whether the dispute prompts a licensing arrangement that unlocks the remaining markets.