Insmed's Brinsupri will reach annual Japanese sales of more than twice its peak forecast within 18 months of listing, exposing Insmed to a ¥9.8 billion price cut.

On 7 October Japan's reimbursement council priced Brinsupri at ¥24,696 a tablet, or about ¥9 million a patient a year. Japan cuts prices by 10 to 25 percent when a cost-based drug sells at twice its forecast. Insmed is at risk because the forecast implies only about 5,400 patients against roughly 800,000 diagnosed cases cited in its own materials. Japan cut Gilead's two hepatitis C drugs by 31.7 percent within a year of their 2015 listing after they beat forecasts. Insmed will surrender part of its windfall to Japan's national insurance budget. A 10–25% price cut will force Insmed to treat roughly 11–33% more Japanese patients just to maintain the same revenue run-rate – turning Brinsupri’s early success into a volume race.