Prescription Patterns of Outpatients and the Potential of Multiplexed Pharmacogenomic Testing.

BACKGROUND Pre-emptive pharmacogenomic (PGx) testing is potentially an efficient approach to improve drug safety and efficacy but the target population to test is unclear. OBJECTIVES We aim to describe the prescription pattern of PGx drugs among adult medical outpatients. METHODS We estimated the 5-year cumulative incidence (CI) for receiving 3 groups of PGx drugs using competing risks analysis: (i) all PGx drugs, (ii) PGx drugs with guidelines and (iii) PGx drugs with serious clinical effects. Comparisons of CIs were also done by patient characteristics using Gray's test. RESULTS The 5-year CIs of receiving any new PGx drug, PGx drug with guidelines, and serious clinical effects were 42.6%, 37.3% and 13.7%, respectively. The 5-year CI of receiving any new PGx drug was higher for patients >40 years old (43.6% vs. ≤40 years old 36.0%, p < 2.2 x 10-22 ), Malays and Indians (50.3% and 49.8% vs. Chinese 31.1%, p < 2.2 x 10-22 ), those who attended one of the following 4 specialties at the index visit compared to other specialties: infectious diseases (46.2% vs. 42.6%, p = 2.9 x 10-4 ), psychiatry (48.3% vs. 42.3%, p = 7.4 x 10-13 ), renal (49.8% vs. 40.9%, p < 2.2 x 10-22 ) and rheumatology & immunology (54.8% vs. 41.7%, p < 2.2 x 10-22 ) and those prescribed ≥5 drugs at index visit (51.7% vs. 0-4 drugs 41.7%, p < 2.2 x 10-22 ). CONCLUSIONS Medical outpatients have a substantial probability of benefiting from pre-emptive PGx testing and this is higher in certain subgroups of patients.