Exposure to multiple drugs with actionable pharmacogenetic biomarkers among older adults in China: a retrospective analysis

This study aimed to estimate the annual prevalence of exposure to multiple CPIC Level A drugs among older adults included in the China Health Insurance Research Association (CHIRA) samples, assess the rank-ordered incremental pharmacogene coverage, and compare the listed testing costs under a specified provincial capped per-locus pricing model. We conducted a retrospective cross-sectional analysis using independently sampled 2015–2017 claims files from CHIRA, focusing on individuals aged ≥65 years. Because cross-year patient linkage was not available, the patient-year record was used as the unit of analysis, and all estimates remained unweighted. We evaluated 53 active ingredients with CPIC Level A guidance, which were included in the CPIC list updated on 28 July 2026 and detected in the analytical medication mapping. The primary exposure was the dispensing of two or more distinct CPIC Level A drugs within a single calendar year, and we also performed an additional analysis with a secondary threshold of five or more distinct drugs. Pharmacogenes were matched from CPIC drug-gene pairs, and we then assessed rank-ordered incremental pharmacogene coverage. We compared the listed charges of separately billed gene tests versus a combined testing panel under the capped per-locus pricing model. Across 3,309,025 patient-year records, 20.2% included exposure to two or more CPIC Level A drugs within a single calendar year. Among these records, 9.3% had exposure to five or more drugs, (accounting for 1.9% of all patient-year records. Among patients prescribed two or more CPIC Level A drugs, atorvastatin was the most common drug (84.2 per 1,000 patient-year records), while among patients prescribed five or more CPIC Level A drugs, pantoprazole was the most frequent (11.9 per 1,000 patient-year records).CYP2C19, SLCO1B1, and CYP2C9 accounted for more than 95% of all mapped exposure among multi-exposed patient-year records. Under the specified capped per-locus fee schedule, the combined gene testing panel had a listed charge of RMB 2,200, while the listed charge of three separately billed gene tests was RMB 2,800. In unweighted annual CHIRA samples, annual exposure to multiple CPIC Level A drugs is common among older adult patient-year records. CYP2C19, SLCO1B1, and CYP2C9 account for the majority of all mapped medication exposure, which highlights that a small core set of pharmacogenes warrants prospective evaluation for the development of targeted pharmacogenomics testing strategies.