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Parenteral anticoagulation

Last updated: April 1, 2021

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Parenteral anticoagulants are routinely indicated for the prevention and treatment of venous thromboembolism. Heparin is typically the preferred agent for inpatient parenteral anticoagulation. Serious side effects include bleeding complications and type 2 heparin-induced thrombocytopenia (HIT), which causes arterial and venous thromboembolism due to an antibody-mediated aggregation of platelets. A drop in platelet count (< 100,000 platelets /μL or decrease of > 50% compared to baseline) may indicate HIT; therefore, the platelet count must be closely monitored in patients on parenteral anticoagulants, especially heparin. If HIT is suspected, treatment involves discontinuing all heparins and beginning nonheparin anticoagulation (usually argatroban).

Unfractionated heparin (UFH)

  • Drug: heparin
  • Administration
    • Prophylaxis: subcutaneous
    • Therapeutic: continuous intravenous infusion
  • Monitoring during therapy: activated partial thromboplastin time (aPTT); , platelet count (including baseline before treatment is started)
  • Clearance: hepatic (preferred agent for patients with renal insufficiency)
  • Antidote: protamine sulfate (a positively-charged protein that can neutralize negatively-charged heparin by forming inactive complexes)

In order to detect heparin-induced thrombocytopenia, platelets must be continuously monitored during heparin therapy and a baseline should be established before commencing treatment.

Low molecular weight heparin (LMWH)

Synthetic heparin

  • Drugs: fondaparinux
  • Administration: subcutaneous
  • Monitoring during therapy
  • Antidote: : possibly activated prothrombin complex concentrates (aPCC)

Heparinoid (glycosaminoglycan)

  • Drugs: danaparoid
  • Administration
    • Prophylaxis: subcutaneous
    • Therapeutic: continuous intravenous infusion
  • Monitoring during therapy: anti-factor Xa activity
  • Antidote: protamine sulfate (partial reversal)

Direct thrombin inhibitors

Unfractionated heparin (UFH)

Low molecular weight heparin (LMWH) and synthetic heparin (fondaparinux)

Direct thrombin inhibitors

  • Directly inhibit thrombin (freely circulating and in association with clots)
  • Act independently from antithrombin

The effect of most parenteral anticoagulants (except for direct thrombin inhibitors) depends on native antithrombin. In patients with antithrombin III deficiency (e.g., due to nephrotic syndrome), this effect is reduced.

General side effects

  • Bleeding
  • Drug-drug interactions

The significantly increased risk of bleeding is the main side effect of all anticoagulants.

Specific side effects


Heparin treatment requires regular monitoring of the platelet count, especially for UFH, even before starting treatment.

We list the most important adverse effects. The selection is not exhaustive.


Low-dose therapy

  • DVT prophylaxis for prolonged bedrest, peri- and postoperative state, immobility

High-dose therapy

Low molecular weight heparin [3]

Direct thrombin inhibitors

Use direct thrombin inhibitors (Bivalirudin, Argatroban, Dabigatran) to treat the BAD HIT (type 2 HIT has a worse prognosis than type 1 HIT).

We list the most important contraindications. The selection is not exhaustive.

Overview of advantages and disadvantages [4]
Unfractionated heparin (UFH) Low-molecular-weight heparin (LMWH)
  • Subcutaneous or intravenous administration
  • Therapeutic administration requires infusion pump
  • Always administer subcutaneously
  • Low dose: subcutaneous administration every 8–12 hrs
  • High dose: intravenous administration with bolus and continuous application via infusion pump
  • Dosage depends on specific drug used, indication, body weight, and kidney function; adjust to body weight and decreased kidney function
  • Effect of LMWH lasts for about 12 hours
  • Monitoring of anti-factor Xa is only necessary in patients with decreased kidney function (and significant over- or underweight); anti-factor Xa activity is measured 4 hrs after administration
  • Short half-life means anticoagulant effect quickly ceases once stopped
  • If used therapeutically, PTT levels have to be monitored frequently (target range: 1.5–2.5-fold prolongation)
  • In comparison with LMWH
    • Type 2 HIT is about 10-fold more common
    • Severe bleeding is more common
Preferred use
  • Emergencies (more easily titrated, available as IV infusion)
  • For patients with advanced renal failure (e.g., in patients with severe renal insufficiency (CrCl < 30mL/min) or the elderly)
  • DVT prophylaxis, outpatient care (longer half-life → fewer injections)
  • Generally preferred to UFH (fewer side effects, easier handling) as long as there are no contraindications


Patients with decreased renal function

  • In severe renal failure: accumulation of LMWH increased bleeding risk → adjust dose or switch to UFH
  1. Katzung B,Trevor A. Basic and Clinical Pharmacology. McGraw-Hill Education ; 2014
  2. Mulloy B, Barrowcliffe T, Gray E. Heparin and low-molecular-weight heparin. Thromb Haemost. 2008; 99 (11): p.807-818. doi: 10.1160/th08-01-0032 . | Open in Read by QxMD
  3. Merli GJ, Groce JB. Pharmacological and clinical differences between low-molecular-weight heparins: implications for prescribing practice and therapeutic interchange.. P & T : a peer-reviewed journal for formulary management. 2010; 35 (2): p.95-105.
  4. Merli GJ, Groce JB. Pharmacological and clinical differences between low-molecular-weight heparins: implications for prescribing practice and therapeutic interchange. P T. 2010; 35 (2): p.95-105.
  5. Herold G. Internal Medicine. Herold G ; 2014
  6. Harter K, Levine M, Henderson SO. Anticoagulation drug therapy: a review. West J Emerg Med. 2015; 16 (1): p.11-17. doi: 10.5811/westjem.2014.12.22933 . | Open in Read by QxMD