Product Entry Sequence and Priority of Follow-on Drug Use: A Case Study of Second-Generation Antipsychotics with Long-Acting Injections

OBJECTIVES: A dominant follow-on pattern has been observed in second-generation antipsychotics (SGA). However, the influence of entry order on priority choice among incident long-acting injection (LAI) users of follow-on drugs was unknown. This study aims to investigate the priority rank of three SGA LAIs, starting with risperidone as the pioneer, followed by paliperidone and aripiprazole.

METHODS: This was a population-based study where new users of SGA LAI with incident schizophrenia were selected between 2009 and 2020 using the National Health Insurance Research Databases in Taiwan. The priority rank for each SGA LAI was defined as the treatment line in the first, second, third, or later position for each user. The monthly predictive probability (PP) of the priority rank of each SGA LAI was estimated using generalized ordinal logistic regression. The monthly aggregates of priority choices for three SGA LAIs were analyzed separately through interrupted time-series analysis with two entries, paliperidone and aripiprazole. We also employed the Chow test to compare changes in the monthly PP of the priority rank between paliperidone and aripiprazole.

RESULTS: There were 144 monthly data points reflecting the priority rank for three SGA LAIs. In risperidone, the PP of attaining the first rank declined (ß=-0.0012, p <0.001), and this trend decreased by 34.4% following the entry of paliperidone (ß=-0.0021, p <0.001), with an additional 9.5% reduction following the entry of aripiprazole (ß=-0.0023, p <0.001). Paliperidone, as the second entry with less innovation, achieved the first rank faster than the first-in-class aripiprazole (ß=0.0036 vs. 0.0022, both p <0.001).

CONCLUSIONS: In the nuanced analysis of market competition based on priority rank, the second entry has a greater impact on existing SGA LAI and achieving the first rank than the third entry, even if the later entry represents a breakthrough innovation. Entry order plays a substantial role in market acquisition among follow-on drugs.