T.M, a 57-year-old man, has thrombophlebitis in the right lower leg. IV heparin, 5000 units by bolus, was given. Following the IV bolus, heparin 5000 units given subQ q6h was prescribed. Other therapeutic means to decrease pain and alleviate swelling and redness were also prescribed.
How does heparin work and why was it prescribed? (USLO 5.2, 5.3, 5.4)
What laboratory test(s) would be monitored for patients taking heparin? Explain your answer. (USLO 5.3, 5.6, 5.8)
Explain the differences between heparin and enoxaparin. Are there advantages to either of these anticoagulants?
Case Context
Patient: T.M, 57-year-old male
Condition: Thrombophlebitis in the right lower leg
Intervention: IV heparin bolus followed by subcutaneous heparin
1. How Heparin Works and Why It Was Prescribed (USLO 5.2, 5.3, 5.4)
Mechanism of Action:
Heparin is an anticoagulant that works by binding to antithrombin III (ATIII).
This binding accelerates ATIII’s ability to inactivate clotting factors, particularly thrombin (factor IIa) and factor Xa.
The result is prevention of further clot formation and extension of existing thrombi.
Heparin does not dissolve clots but prevents them from growing, allowing the body’s natural fibrinolytic system to break them down.
Why Prescribed in Thrombophlebitis:
Thrombophlebitis involves inflammation of a vein with clot formation.
Heparin reduces the risk of clot propagation and embolization (e.g., pulmonary embolism).
It provides rapid anticoagulation, especially with IV bolus dosing, followed by maintenance with subcutaneous injections.
2. Laboratory Tests Monitored for Patients Taking Heparin (USLO 5.3, 5.6, 5.8)
Activated Partial Thromboplastin Time (aPTT):
Primary test used to monitor unfractionated heparin therapy.
Measures the intrinsic and common pathways of coagulation.
Therapeutic range: typically 1.5–2.5 times the normal control value.
Ensures adequate anticoagulation without excessive bleeding risk.
Platelet Count:
Monitored to detect heparin-induced thrombocytopenia (HIT), a serious immune-mediated adverse effect.
Other Monitoring:
Signs of bleeding (e.g., hematuria, GI bleeding, bruising).
Hemoglobin/hematocrit levels to assess for occult blood loss.
3. Differences Between Heparin and Enoxaparin
Feature Heparin (Unfractionated Heparin, UFH) Enoxaparin (Low Molecular Weight Heparin, LMWH)
Source Derived from animal mucosa Chemically modified, smaller fragments
Mechanism Inhibits thrombin (IIa) and factor Xa via ATIII Primarily inhibits factor Xa via ATIII; less effect on thrombin
Administration IV bolus + continuous infusion or subQ SubQ only; predictable absorption
Monitoring Requires aPTT monitoring Usually does not require routine monitoring (predictable pharmacokinetics)
Half-life Short (about 1–2 hours) Longer (about 4–6 hours)
Risk of HIT Higher Lower, but still possible
Reversal Protamine sulfate effective Protamine partially effective
4. Advantages of Each Anticoagulant
Heparin (UFH):
Rapid onset of action (IV bolus).
Easily reversible with protamine sulfate.
Preferred in situations requiring quick titration (e.g., unstable patients, procedures).
Enoxaparin (LMWH):
More predictable anticoagulant response.
Longer half-life allows less frequent dosing.
Lower risk of HIT.
No need for routine aPTT monitoring, making it convenient for outpatient use.
Often preferred for long-term management of venous thromboembolism.
Summary
Heparin was prescribed to T.M to prevent clot extension and embolization in thrombophlebitis.
aPTT and platelet counts are monitored to ensure therapeutic anticoagulation and detect HIT.
Enoxaparin differs from heparin in its mechanism, dosing, monitoring requirements, and safety profile.
Advantages: Heparin is useful for rapid, reversible anticoagulation in acute settings, while enoxaparin offers convenience and safety for longer-term management.
