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Unfractionated heparin dosing in obese patients

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Abstract

Background The effect of obesity on the pharmacokinetics and pharmacodynamics of unfractionated heparin is not clearly understood, therefore to reduce the risk of bleeding, maximal dose (capped) nomograms are often used. This can lead to inadequate anticoagulation and increased mortality and morbidity. In Queensland, Australia, statewide nomograms recommend total-body-weight-based dosing, with capped initial bolus and maintenance doses. Objective To determine if current practices for unfractionated heparin dosing leads to inadequate anticoagulation in obese patients. Setting Princess Alexandra Hospital, Queensland, Australia. Method A retrospective audit of unfractionated heparin dosing in 200 patients divided into cohorts of; < 100 kg (defined as non-obese), 100–124.9 kg, 125–150 kg and > 150 kg, Main outcomes measured Mean maintenance doses in U/h and U/kg/h required to achieve two consecutive therapeutic activated partial thromboplastin times’ and the corresponding time to achieve this endpoint. Results The mean ± standard deviation maintenance doses required to achieve two consecutive therapeutic activated partial thromboplastin times’ in U/h were 1229 ± 316, 1673 ± 523, 2031 ± 596 and 2146 ± 846, and in U/kg/h were 16 ± 4.1, 15.1 ± 4.8, 14.9 ± 4.2 and 11.6 ± 4.2 for the weight cohorts respectively. The median time (inter-quartile range) to therapeutic activated partial thromboplastin times’ for obese patients was 39 (21.5–56) h. Conclusions Our results suggest inadequate dosing in obese patients. We recommend the use of larger absolute doses (U/h) of nfractionated heparin but reduced uncapped total body weight-based doses-(U/kg/h) as patient weight increases.

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Acknowledgements

Nicholas Matigian (Queensland Cyber Infrastructure Foundation Ltd) for his help in statistical analysis, Neil Cottrell (University of Queensland) for his help in initial manuscript revisions.

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Authors and Affiliations

  1. School of Pharmacy, Pharmacy Australia Centre of Excellence, University of Queensland, Brisbane, QLD, Australia

    Christopher George, Michael Barras, Judith Coombes & Karl Winckel

  2. Pharmacy Department, Princess Alexandra Hospital, Brisbane, QLD, Australia

    Christopher George, Michael Barras, Judith Coombes & Karl Winckel

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Appendix 1: Queensland health unfractionated heparin nomogram [12]

Appendix 1: Queensland health unfractionated heparin nomogram [12]

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George, C., Barras, M., Coombes, J. et al. Unfractionated heparin dosing in obese patients. Int J Clin Pharm 42, 462–473 (2020). https://doi.org/10.1007/s11096-020-01004-5

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