HEPARIN SODIUM
Clinical safety rating: safe
Other drugs that affect hemostasis increase bleeding risk Can cause heparin-induced thrombocytopenia (HIT) and bleeding.
Heparin sodium potentiates the activity of antithrombin III, thereby inactivating thrombin and factor Xa, leading to inhibition of coagulation.
| Metabolism | Heparin is primarily metabolized in the liver and also in the reticuloendothelial system; it undergoes desulfation and depolymerization. |
| Excretion | Heparin is cleared primarily via the reticuloendothelial system and liver, with minimal renal excretion. Unchanged heparin is not significantly excreted in urine. Biliary/fecal elimination is negligible. |
| Half-life | The terminal elimination half-life of heparin is dose-dependent: approximately 30 minutes (low dose, e.g., 25 U/kg), 60 minutes (medium dose, 100 U/kg), and 150 minutes (high dose, 400 U/kg). Half-life increases with dose due to saturation of clearance mechanisms. |
| Protein binding | Heparin is highly protein-bound (approximately 85-97%), primarily to antithrombin III (ATIII), with minor binding to other plasma proteins including albumin, fibrinogen, and lipoproteins. |
| Volume of Distribution | Apparent volume of distribution ~0.05-0.1 L/kg (small, reflecting plasma volume). Heparin remains largely in the intravascular space and does not distribute extensively into tissues. |
| Bioavailability | Subcutaneous: ~30-40% (low and variable due to poor absorption and first-pass hepatic clearance). IV: 100%. |
| Onset of Action | IV: immediate (within minutes). Subcutaneous: 20-60 minutes (delayed due to absorption). |
| Duration of Action | IV: 2-6 hours (dose-dependent). Subcutaneous: 4-12 hours (prolonged effect due to continued absorption). Note: Protamine sulfate reversal shortens duration. |
Intravenous: Initial bolus of 80 units/kg, then continuous infusion at 18 units/kg/h. Subcutaneous: 5000 units every 8-12 hours for prophylaxis.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment for GFR; however, accumulation may occur in severe renal impairment (CrCl <30 mL/min), requiring monitoring of aPTT and dose titration. |
| Liver impairment | No specific Child-Pugh based dose adjustments; use with caution in severe hepatic impairment due to increased bleeding risk, monitor aPTT. |
| Pediatric use | Intravenous: Bolus of 75-100 units/kg, then initial infusion of 20 units/kg/h; adjust based on aPTT. Subcutaneous: 50-100 units/kg every 12 hours for prophylaxis. |
| Geriatric use | Elderly patients may have reduced renal function; consider lower initial doses and close aPTT monitoring to avoid bleeding. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Other drugs that affect hemostasis increase bleeding risk Can cause heparin-induced thrombocytopenia (HIT) and bleeding.
| FDA category | Human |
| Breastfeeding | Not excreted into breast milk due to large molecular weight; considered compatible with breastfeeding. M/P ratio not applicable. |
| Teratogenic Risk | Heparin does not cross the placenta due to its high molecular weight. No known teratogenic effects in any trimester. Risk of maternal hemorrhage and fetal complications associated with maternal anticoagulation, but heparin is considered safe during pregnancy when indicated. |
■ FDA Black Box Warning
Heparin is not intended for intramuscular use due to risk of hematoma. Spinal/epidural hematomas can occur in patients receiving anticoagulants and undergoing neuraxial anesthesia or spinal puncture, resulting in long-term or permanent paralysis. Monitor for signs and symptoms of neurological impairment.
| Common Effects | bleeding |
| Serious Effects |
Hypersensitivity to heparin, history of heparin-induced thrombocytopenia, active major bleeding, severe thrombocytopenia, and when suitable coagulation tests cannot be performed.
| Precautions | Risk of hemorrhage, heparin-induced thrombocytopenia (HIT), heparin-induced thrombocytopenia with thrombosis (HITTS), osteoporosis with prolonged use, hyperkalemia due to suppression of aldosterone, and hypersensitivity reactions. Monitor platelet counts and coagulation parameters regularly. |
| Food/Dietary |
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| Fetal Monitoring | Monitor maternal platelet count (risk of heparin-induced thrombocytopenia), signs of bleeding, and anti-Xa levels if unfractionated heparin used. For fetus: monitor for signs of placental abruption or bleeding via ultrasound if clinically indicated. |
| Fertility Effects | No known adverse effects on fertility. Heparin does not interfere with ovulation, implantation, or spermatogenesis. |
| No specific food restrictions, but avoid excessive intake of vitamin K-rich foods (e.g., leafy greens) as they may theoretically reduce heparin effects; however, clinically significant interactions are rare. Avoid alcohol consumption due to increased bleeding risk (ethanol potentiates anticoagulation). |
| Clinical Pearls | Use weight-based dosing for acute VTE; obtain baseline aPTT, PT, CBC, and platelets. Monitor aPTT 6h after bolus and q6h until therapeutic (1.5-2.5x control). Heparin resistance may occur with antithrombin deficiency or high factor VIII. Reversal with protamine sulfate (1mg per 100U heparin given in last 4h). Avoid in history of HIT; alternative anticoagulation needed. Use with caution in renal impairment (heparin is renally cleared) and elderly. Intramuscular injections contraindicated due to hematoma risk. |
| Patient Advice | Do not skip doses or stop heparin without physician advice. · Report any signs of bleeding: unusual bruising, blood in urine/stool, bleeding gums, prolonged bleeding from cuts. · Avoid aspirin, NSAIDs, and other blood thinners unless prescribed by your doctor. · Use an electric razor and soft toothbrush to minimize bleeding risk. · Inform all healthcare providers that you are taking heparin before any procedure or surgery. · Seek emergency care if you experience severe headache, abdominal pain, joint swelling, or difficulty breathing. · For outpatient use: rotate injection sites (abdomen, thigh) and do not massage the site after injection. |