In this episode I’ll:

1. Discuss an article about high dose heparin for VTE prophylaxis in obese patients.

2. Answer a drug information question about vitamin K.

3. Share a resource for lab assay interference by non-vitamin K oral anticoagulants.

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Article

Safety and Efficacy of High-Dose Unfractionated Heparin for Prevention of Venous Thromboembolism in Overweight and Obese Patients

Lead author: Mishna Joy

Available online pre-publication from the journal Pharmacotherapy

Objective

The authors sought to determine the safety and efficacy of high-dose subcutaneous unfractionated heparin (UFH) for prevention of venous thromboembolism (VTE) in overweight and obese patients.

Methods

The study was a single-center, retrospective, observational cohort study. It was completed in an academic tertiary care center and examined 1335 adult patients who weighed over 100 kg. Patients received either subcutaneous UFH 7500 units every 8 hours (751 patients [high-dose group]) or 5000 units every 8 hours (584 patients [low-dose group]) for inpatient VTE prophylaxis.

Results

The authors reported that the incidence of VTE was similar for patients in the high-dose group versus those in the low-dose group for all BMI categories. Bleeding complications were significantly higher for patients in the high-dose group. The proportion of patients with at least a 2-g/dl hemoglobin drop from admission was higher in patients in the high-dose groups in obese classes II (BMI 35-40) and III (BMI >40). In addition, the proportion of patients who received at least 2 units of packed red blood cell transfusion was significantly higher in patients in the high-dose group who were in obese class III: 11% in the high-dose group versus 5% in the low-dose group.

Conclusion

The authors concluded that:

Administering a higher dose of heparin to patients weighing more than 100 kg may not impart additional efficacy in reducing the incidence of VTE. However, it may increase the risk for bleeding.

Discussion

The authors included ICU and medical floor patients in the study. Curiously, they found that bleeding complications occurred more frequently in the medical floor patients compared to ICU patients. I was surprised that an increase in efficacy for VTE prevention did not accompany the higher risk of bleeding in patients in the high-dose group. The authors fell a few hundred patients short of their stated goal to achieve 80% power; therefore the increased need for transfusion may apply to all BMI categories. A larger, multi-center study could help determine this.

Drug information question

“Pharmacy Brendon” in the Pharmacy Nation Slack group asks:

Q: Has anyone seen a document that correlates vitamin K dose to INR lowering? (i.e 1 mg lowers INR by X on average)

A: This reference cited by the CHEST guidelines is the closest I’ve seen.

The reference states for non-bleeding patients:

A recent cumulative analysis of the available literature does suggest, however, that the optimal dose of oral vitamin K is 1–1.25 mg for patients with INR values between 4.5–10.0, and 2.5 mg for patients with INR values of more than 10.0.

Resource

The American College of Cardiology maintains a table that lists the effects of the non-vitmain K antagonist oral anticoagulants on various anticoagulation assays. The table includes known effects on the PT/INR, aPTT, TT, Anti-Xa activity for each drug, and includes a recommendation on the best assay to use for monitoring.

If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.

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