Efient was launched in the UK in 2009. This was followed by a two year honeymoon period, which ended in 2011 when the first parallel imports appeared on the UK retail market.
For the first three months just one company was selling the Efient PI. However, this grew so that by Jan 2013 there were 13 companies selling the PI and 36 price list offers for these products per month. The number of PI suppliers reached a maximum in Oct 2015 at 15, and the number of market offers was at its highest in December 2013 at 45. Between 2013 and 2022 the number of suppliers has averaged about 10, but the number of price list offers did decline between 2015 and 2019 which may reflect a reduction in the available stock.
Then Efient lost its exclusivity and patent protection in March 2019, which while it did not decrease the number of suppliers selling PI or the number of price lists, did stabilise the market so that both metrics remained stable. Normally as the branded share of market declines the number of prescriptions available for the PI also declines. This will eventually reduce both metrics, and with just 74 branded Efient prescriptions in England in July 2022 this is not likely to be very long.
The message for other brands is that after launch you can hope for a two year honeymoon period before PIs appear. Then PIs will grow to reduce your UK sales. The number of suppliers selling the PI will stabilise eventually at about 10, and this will remain the case even after generics have been launched. You can either decide to compete on price with PIs (brand equalisation), but this usually means you are competing with another division of your own company. Alternately you can monitor PI activity and get your targets reduced. Brand equalisation is a real possibility when generics have been launched, but until you lose exclusivity PIs will always be an irritant.