Acenocoumarol is the most widely prescribed vitamin K antagonist (VKA)
to prevent and treat thromboembolic disorders. It keeps a major place in
many indications despite the introduction of new direct oral
anticoagulants (DOACs). However, a narrow therapeutic range, an
intra-individual variability and drug interactions may lead to serious
adverse drug reactions. Sometimes, a genetic or acquired resistance to
this drug may lead to a risky situation. Hopefully, resistance to
acenocoumarol is a very rare phenomen.
Here in we present an unsusual case of a suspected resistance to
acenocoumarol. This case was notified to the Tunisian National Center of
Pharmacovigilance on October 2017 and registered under the number
2449/2017.
A 67-year-old patient with hypertension, diabetes, and coronary disease
was treated with captopril, atenolol, atorvastatin, and salicylic acid.
In 2017, acenocoumarol treatment was introduced. At biological control,
the prothrombin time (PT) was 100%. The doses of acenocoumarol were
raised progressively with iterative controls of PT. PT was always 100%
even when acenocoumarol reached the dose of 2 g/day. A resistance to
acenocoumarol was suspected. The patient was referred to
pharmacovigilance department for case analysis. During the patient
interview, we discover that the patient was confusing acenocoumarol with
atenolol. In fact, when his doctor was increasing the doses of
acenocoumarol, the patient increased her intake of atenolol believing
that it was acenocoumarol.
A resistance to acenocoumarol was eliminated in this patient since she
had never taken the drug. We highlight through this case the importance
of patient’s interview. Explaining the indications and the potential
adverse events of the drug to patients taking VKA is crucial to ensure a
better efficiency of treatment without increasing the risk of bleeding
complication.