Unfractionated heparin dosing in obese patients

Area of Science:

• Pharmacology
• Clinical Pharmacy
• Critical Care Medicine

Background:

• Obesity's impact on unfractionated heparin (UFH) pharmacokinetics and pharmacodynamics is not well understood.
• Current capped dosing nomograms for UFH in obese patients may lead to underdosing, increasing risks of bleeding, mortality, and morbidity.
• Statewide nomograms in Queensland, Australia, utilize total-body-weight-based UFH dosing with capped initial bolus and maintenance doses.

Purpose of the Study:

• To evaluate whether current UFH dosing practices result in inadequate anticoagulation in obese patients.
• To assess the relationship between patient weight and UFH dosage requirements for achieving therapeutic anticoagulation.

Main Methods:

• Retrospective audit of UFH dosing in 200 patients at Princess Alexandra Hospital, Queensland, Australia.
• Patients were categorized into weight cohorts: <100 kg (non-obese), 100-124.9 kg, 125-150 kg, and >150 kg.
• Key outcomes measured included mean maintenance doses (U/h and U/kg/h) and time to achieve two consecutive therapeutic activated partial thromboplastin times (aPTTs).

Main Results:

• Mean maintenance UFH doses (U/h) increased with weight cohorts, while doses in U/kg/h decreased.
• Obese patients required significantly longer times to achieve therapeutic aPTTs, with a median of 39 hours (IQR 21.5-56).
• The heaviest cohort (>150 kg) showed the lowest U/kg/h maintenance dose (11.6 ± 4.2 U/kg/h).

Conclusions:

• Current UFH dosing practices appear inadequate for obese patients, potentially leading to subtherapeutic anticoagulation.
• Recommendations include using higher absolute UFH doses (U/h) for obese patients.
• Consideration should be given to reduced, uncapped total body weight-based UFH doses (U/kg/h) as patient weight increases.