Beware of thromboembolic risk in obese patients on direct oral anticoagulants (DOACs)

Letters should ideally be limited to 350 words, and sent by email to: clinicalmedicine@rcplondon.ac.uk Editor - We read with interest the article by Burden et al on pulmonary embolism in a patient on rivaroxaban and concurrent carbamazepine.1 While the authors highlight the interaction between rivaroxaban and carbamazepine, one should be mindful of other risk factors that might reduce the therapeutic efficacy of a direct oral anticoagulant (DOAC), namely severe obesity, possibly due to suboptimal dosing regime in such patients.Results indicated that patients with higher body weights had lower peak concentrations, increased volume of distribution and shorter half-lives of DOACs.3'4 Although dose adjustment of DOACs in severely obese patients are still not recommended on the product literature, expert guidance suggests avoiding DOACs in patients with a BMI of >40 kg/m2, or a weight of >120 kg.4 If DOACs are used in such patients, they recommend checking drug-specific peak and trough levels and substituting it with a vitamin K antagonist if the levels are below the expected range, rather than adjusting the DOAC dose.4 It is important to raise awareness of clinicians on this matter as venous and arterial thromboembolic events while taking DOACs account for 3-5% of adverse events that are reported to the Medicines and Healthcare products Regulatory Agency (MHRA).5 While there is a need for more data on the efficacy of DOACs on obese patients, we also need guidance on the most appropriate anticoagulation regime for patients who suffer a thromboembolic episode despite being on a DOAC. ?Effect of extremes of body weight on the pharmacokinetics, pharmacodynamics, safety and tolerability of apixaban in healthy subjects.