Phenprocoumon Dose Requirements, Dose Stability and Time in Therapeutic Range in Elderly Patients With and Polymorphisms.

Background: Dose requirements of vitamin K antagonists are associated with and , but, compared to warfarin, less data is available about phenprocoumon. Furthermore, the effects on dose stability and anticoagulation quality are still unclear.

Methods: Aim was to scrutinize phenprocoumon dose requirements, dose stability and anticoagulation quality in association to and in a natural cohort of elderly primary care patients. As a subgroup within the IDrug study, phenprocoumon treated patients with at least two INR values within three months before enrollment (n = 209) were analyzed concerning average weekly dose, standard deviation of weekly dose (intra-subject variability), constant dose (yes/no), average INR and TTR grouped by and (and combinations).

Results: Average weekly dose per patient was 14.4 ± 5.3 mg, 11.9 ± 4.0 mg and 11.2 ± 4.3 mg in wildtypes, and carriers (p < .0001) and 16.0 ± 4.2 mg, 13.3 ± 5.1 mg and 8.0 ± 2.7 mg per week in CC, CT and TT genotypes, respectively (p < .0001). Significant differences concerning intra-subject variability were detected among all groups (p < .0001) with the smallest variability in carriers. TTR medians were 75.4%, 79.4% and 100% in wildtypes, and carriers, respectively (p = 0.0464). The proportion of patients with perfect control was highest among carriers, but this result was not significant (p = 0.0713).

Discussion: Our analyses support the results of previous investigations regarding genotype-associated dose requirements and raise the hypothesis that dose stability and anticoagulation quality may be increased in carriers. However, our data should be treated cautiously due to the small sample size.

Clinical Trial Registration: German Clinical Trials Register, identifier DRKS00006256.