metabolised by CYP2C9, suggests that our results are not likely
to be explained by drug-drug interactions. In addition, differences
in lipophilicity of statins are also unlikely to account for the
differences found between statins as rosuvastatin is hydrophilic
while simvastatin is lipophilic. A potential other explanation is
that statins do reduce coagulation, which was suggested by
Sahebkar et al. because D-dimer levels decreased after 3 months
of statin therapy and because D-dimer levels are markers of
coagulation [14]. To get more insight whether simvastatin and
rosuvastatin have anticoagulant properties, a next step would be
to investigate the effect of these statins on coagulation in patients
not on VKAs.
Though the current study is of etiological interest as
it gives a lead why statins might be able to decrease
venous thrombosis risk, its clinical effect appears to be
minimal: INRs did not increase immediately and only
marginally, and the VKA dose reduction was also
minimal.
A potential limitation of our study is that co-medication
was self-reported and the only statin reported by the pharmacy
to the anticoagulation clinics was rosuvastatin.
Consequently, there may be discrepancies between the
medication records of the anticoagulation clinics and what
the patients used. As patients were compared with themselves,
we expect that this has not influenced the results.
An additional limitation is that we excluded patients who were
hospitalised between the INR measurement before and after statin
initiation.We did this because the assumption of the study, that
there are no other environmental changes present that can affect
VKA dosage and/or INR in the patient except that the patient
started with statin, is otherwise not held. For that reason, we
could have missed patients of more ‘dramatic’ changes of
anticoagulation, like patients with a major bleed. Furthermore,
pharmacokinetics of the two studied VKAs do differ, for example
phenprocoumon has a longer half-life as compared with
acenocoumarol [12]. However, differences in pharmacokinetics
of the VKAs tested are unlikely to have contributed to the statin
results found in this study as results were similar in both
acenocoumarol and phenprocoumon users. Another limitation
is that we assumed that patients are compliant to their statin
therapy. It is likely that not all patients were fully compliant as
previous studies showed an average adherence to statins of 71–
77 % [15]. Our results could therefore be diluted and the effects
on VKA dosage are likely to be stronger if we could have taken
statin adherence into close account. A final limitation of our
study is that the dosage of statins was not registered in the electronic
system. Therefore, no analyses could be performed that
took the dosage of statin into account.
In conclusion, we found that statin treatment was associated
with a minor although statistically significant decrease in
VKA dosage in both phenprocoumon and acenocoumarol
users, which suggests that statins may have anticoagulant
properties.
Acknowledgments
Author contributions N. van Rein was the principle investigator of the
study. N. van Rein and J.S. Biedermann collected data for the study. All
authors had full access to the data. N. van Rein performed statistical
analyses and W.M. Lijfering supervised the statistical analysis. N. van
Rein, J.S. Biedermann and S.M. Bonafacio interpreted the data. All authors
discussed the results and drafted and revised the manuscript.
Compliance with ethical standards
Sources of funding N. van Rein was supported by Innovative
Coagulation Diagnostics at the Center for Translational Molecular
Medicine [grant number 01C-201] and W.M. Lijfering is a Postdoc of
the Netherlands Heart Foundation [grant number 2011 T 12].
Conflict of interest The authors declare that they have no conflict of
interest.
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