A lack of validated on-therapy ranges for the novel oral anticoagulants (NOACs) contributes to the difficulty in managing obese patients with conditions such as pulmonary embolism (PE) or deep vein thrombosis (DVT), a haematology meeting has heard.
In addition, there is a lack of pharmacokinetic and clinical data to guide prescribing especially in patients at extremes of weight such as those weighing more than 150kg or with a BMI greater than 40.
Dr Georgia McCaughan, an advanced haematology trainee at Westmead Hospital, told the Blood 2018 conference in Brisbane that a prospective registry aimed to help rectify the lack of clinical data.
The Australian and New Zealand Registry of Anticoagulation in the Obese is currently collecting data from four sites in Australia and two in New Zealand and looking to expand.
“We want to see whether these obese patients are having equivalent clinical outcomes especially on the [NOACs], whether they are achieving appropriate drug levels and if not, whether there is a role for dose adjustment in these patients.”
The 78 patients registered to date have a median age of 53 years, weight of 122kg (range 76-290 kg) and a median BMI of 43.4 (range 35-87.5).
While the numbers of patients using each anticoagulant were still small, she said there was a trend towards the patients on warfarin and low molecular weight heparin (LMWH) being slightly heavier.
The group of patients on LMWH was enriched with patients with active malignancy perhaps associated with an increased risk of bleeding.
A 2018 review of anticoagulation at the extremes of body weight co-authored by Dr McCaughan showed weight was less important with vitamin K antagonists.
However the evidence suggested weight did contribute to variability in NOAC concentrations.
Dr McCaughan said all registry patients on apixaban had peak and trough drug levels that fell within the therapeutic range.
“Four of 12 patients on rivaroxaban had peak levels that fell below on-therapy ranges but had appropriate trough levels.”
She said an appropriate dosing strategy remained unclear especially in the heavier patients but ‘we’ve taken the approach of dose capping at 150mg’.