Recurrent venous thrombosis under rivaroxaban and carbamazepine for symptomatic epilepsy

Abstract

Background

The direct oral anticoagulant (DOAC) rivaroxaban, an oral Factor Xa inhibitor, is increasingly used as an alternative to vitamin-K-antagonists (VKAs). Absorption and elimination of DOACs are dependent on the permeability glycoprotein (P-gp) efflux transporter protein system, and DOACs are substrates of the hepatic cytochrome P 450 3A4 (CYP3A4) enzymes. Therefore, drug-interactions may occur when DOACs are administered with drugs affecting the activity of P-gp or CYP3A4 systems. Several antiepileptic drugs like carbamazepine are known to affect P-gp and CYP3A4-activity.

Case report

A 55-year-old male was admitted because of pain and swelling of his right leg spontaneously since 2 days. He was under a therapy with 20mg rivaroxaban since 4 months because of an unprovoked venous thrombosis of his right leg. He had a history of poliomyelitis at age 6 months, structural epilepsy due to poly-microgyria with complex partial seizures with secondary generalization since age 6 years, why he was treated with carbamazepine (900mg/d). He reported to be highly adherent to his anticoagulant and antiepileptic medication. Anti-Xa activity was <20ng/ml according to a rivaroxaban calibrated anti-factor Xa assay. Therapy with rivaroxaban was stopped, and low-molecular-weight heparin, followed by phenprocoumon, was started.

Conclusion

The combination of DOACs with carbamazepine, an inducer of P-gp and CYP3A4-activity, should be avoided since the anticoagulant effect is decreased. There is an urgent need to increase our knowledge and physicians’ awareness about the potential of drug–drug interactions of DOACs.