Age-stratified outcome of a genotype-guided dosing algorithm for acenocoumarol and phenprocoumon

Background Age seemed to affect the interaction between coumarins and genotype in the acenocoumarol and phenprocoumon arm of the European Pharmacogenetics of Anticoagulant Therapy (EU-PACT) trial. Objectives To investigate the effect of genotype-guided dosing stratified by age and the potential factors causing a difference. Patients/Methods Data from the acenocoumarol/phenprocoumon arm of the EU-PACT trial were used. The percentages of time below the therapeutic range, time above the therapeutic range and time in the therapeutic range (TTR) during the initial 12 weeks of therapy were compared between the genotype-guided group and the control group among younger (< 75 years) and older ( 75 years) patients by the use of independent t-tests, and adjusted for sex, height, weight and co-medications by the use of linear regression. Results Among younger phenprocoumon users, TTR during the first 12 weeks in the genotype-guided group (n = 55) was 9.5% (95% confidence interval [CI] 1.3 to 17.8) higher than in the control group (n = 63), with a remarkably lower percentage of time above this range (difference: - 9.6%, 95% CI - 19.0 to - 0.2) and a similar time below this range. Older patients dosed by the genotype-guided algorithm (n = 24) spent more time above the range (difference: 27.5%, 95% CI 12.9 to 42.0). For acenocoumarol users, there were no significant differences between the genotype-guided and control groups for most outcomes, except for a lower percentage of time below the range among older patients. Conclusions The genotype-guided algorithm for phenprocoumon in the EU-PACT trial benefitted younger patients more, but for older patients the algorithm needs to be revised and tested in further research.