We evaluated the effectiveness of genotype- versus phenotype-directed individualization for use of P2Y12 inhibitors to decrease high on-treatment of platelet reactivity (HOPR). Sixty-five patients undergoing percutaneous coronary intervention for non-ST elevation acute coronary syndromes were randomly assigned to genotype- or phenotype-directed treatment. All patients were screened for the CYP2C19 *2, *3, or *17 alleles by using Verigene CLO assay (Nanosphere, Northbrook, IL, USA). On-treatment platelet reactivity was measured using the VerifyNow P2Y12 assay (Accumetrics, San Diego, CA, USA). 21 CYP2C19 *2 or *3 carriers (65.6%) or 11 patients with HOPR (33.3%), defined as ≥230 of P2Y12 reaction unit (PRU), were given 90 mg ticagrelor twice daily; non-carriers or patients without HOPR were given 75 mg clopidogrel daily. The primary endpoint was the percentage of patients with HOPR after 30 days of treatment. PRU decreased following both genotype- and phenotype-directed therapies (242±83 vs. 109±90, p<0.001 in the genotype-directed group; 216±74 vs. 109±90, p=0.001 in the phenotype-directed group). Five subjects (16.2%) in genotype-directed group and one (3.3%) in the phenotype-directed group had HOPR at day 30 (p=0.086). All patients with HOPR at the baseline who received ticagrelor had a PRU value of <230 after 30 days of treatment. Conversely, clopidogrel did not lower the number of patients with HOPR at the baseline. Tailored antiplatelet therapy according to point-of-care genetic and phenotypic testing is feasible and effective in decreasing HOPR after 30 days.
