Clinical safety rating: safe
Human studies have proved safety
Heparin binds to antithrombin III, inducing a conformational change that accelerates the inactivation of thrombin (factor IIa) and factor Xa, thereby inhibiting coagulation.
| Metabolism | Heparin is metabolized via the reticuloendothelial system and partially depolymerized by heparinases in the liver; renal excretion of metabolites and parent drug occurs. |
| Excretion | Primarily cleared via reticuloendothelial system and metabolism; renal excretion of unchanged drug is minimal (<5%). |
| Half-life | 0.5–2 hours (dose-dependent; at therapeutic doses, ~1–2 h; with higher doses, up to 2.5 h). Clinical context: shorter half-life in pulmonary embolism; prolonged in hepatic or renal impairment. |
| Protein binding | High, ~95% (primarily to antithrombin III, but also to albumin, lipoproteins, and fibrinogen; binding saturable). |
| Volume of Distribution | 0.05–0.07 L/kg (confined to plasma volume; minimal extravascular distribution). |
| Bioavailability | SC: 20–30% (with significant interindividual variability; higher doses yield lower relative bioavailability due to saturable absorption). IV: 100%. |
| Onset of Action | IV: immediate; SC: 20–30 minutes (with a lag of 1–2 h for peak effect). |
| Duration of Action | IV: 2–4 hours (dose-dependent, aPTT returns to baseline ~4–6 h after bolus); SC: 8–12 hours (dose-dependent). Clinical note: low-dose SC (prophylaxis) may have shorter duration. |
| Molecular Weight | 15000 |
Intravenous: Initial bolus of 80 units/kg (or 5000 units) followed by continuous infusion of 18 units/kg/h (or 1300 units/h), adjusted to maintain aPTT 1.5-2.5 times control. Subcutaneous: 5000 units every 8-12 hours for prophylaxis.
| Renal impairment | No specific dose adjustment for GFR; however, renal impairment may prolong heparin half-life and increase bleeding risk; monitor aPTT and adjust infusion accordingly. For severe renal impairment (CrCl <30 mL/min), consider reduced doses or alternative anticoagulant. |
| Liver impairment | No specific Child-Pugh based guidelines; use with caution in hepatic impairment due to increased bleeding risk. Monitor aPTT and adjust dose as needed. |
| Pediatric use | Intravenous: Bolus 75-100 units/kg over 10 minutes, then continuous infusion 20-25 units/kg/h (infants) or 18-20 units/kg/h (children). Adjust to maintain aPTT 60-85 seconds. Subcutaneous: 100-150 units/kg every 12 hours for prophylaxis. |
| Geriatric use | Elderly patients may have reduced renal function and increased bleeding risk; consider lower initial bolus (e.g., 50-75 units/kg) and infusion rates (e.g., 15 units/kg/h), and monitor aPTT frequently. |
| 1st trimester | Heparin does not cross the placenta due to its high molecular weight and negative charge; no known teratogenic effects in first trimester. |
| 2nd trimester | Safe to use; no increased risk of fetal harm; monitored for maternal hemorrhage risk. |
| 3rd trimester | Safe to use; may increase risk of maternal hemorrhage at delivery; consider discontinuation or reversal prior to delivery. |
Clinical note
Safe in pregnancy. Unfractionated heparin does not cross the placenta due to its large molecular size. Preferred over LMWH in specific scenarios: near delivery (allows complete reversal with protamine), in patients with renal impairment (where LMWH is less predictable), and for acute PE requiring thrombolysis or catheter-directed therapy. Requires aPTT monitoring. Long-term use associated with heparin-induced osteoporosis and thrombocytopenia (HIT); LMWH preferred for long-term use.
| Placental transfer | Does not cross placenta. |
| Breastfeeding |
■ FDA Black Box Warning
Heparin can cause heparin-induced thrombocytopenia (HIT), a serious immune-mediated reaction leading to thrombocytopenia and thrombosis. Spinal or epidural hematomas can occur with concurrent neuraxial anesthesia or spinal puncture, resulting in permanent paralysis.
| Common Effects | Injection site reactions pain swelling redness |
| Serious Effects |
History of heparin-induced thrombocytopenia (HIT)Active major bleedingSevere uncontrolled hypertensionRecent central nervous system surgery or traumaKnown hypersensitivity to heparin
| Precautions | Monitor platelet counts regularly for HIT, Risk of hemorrhage, especially in patients with bleeding disorders or recent surgery, Avoid intramuscular injection due to risk of hematoma, Heparin resistance may occur in some patients, Protamine sulfate is the antidote for overdose |
| Food/Dietary |
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| Heparin does not pass into breast milk due to its large molecular size and poor oral bioavailability; considered compatible with breastfeeding. |
| Lactation Rating | L1 (Safe) |
| Teratogenic Risk | Heparin does not cross the placenta due to high molecular weight and negative charge; no known teratogenic effects in first trimester. In second and third trimesters, risk of maternal hemorrhage, thrombocytopenia, and osteoporosis; fetal risk primarily indirect via maternal complications. No structural teratogenicity reported. |
| Fetal Monitoring | Monitor maternal aPTT (target 1.5-2.5 times control), platelet count (daily for first 14 days then periodically), signs of bleeding, and fetal growth with ultrasound if prolonged use. Consider monitoring for heparin-induced thrombocytopenia (HIT). |
| Fertility Effects | No direct adverse effects on fertility reported. Heparin does not affect ovulation, implantation, or spermatogenesis. May be used during assisted reproductive technology for thromboembolism prophylaxis. |
| Avoid excessive vitamin K-rich foods (green leafy vegetables, liver) as they may counteract anticoagulant effect. No other specific food restrictions; maintain consistent intake of vitamin K-rich foods to avoid fluctuations in INR if transitioning to warfarin. Alcohol may increase bleeding risk; limit intake. |
| Clinical Pearls | Monitor aPTT 6 hours after initiation and dose changes; target 1.5-2.5 times control. Use weight-based dosing for DVT/PE. Reverse with protamine sulfate (1 mg per 100 units UFH). Heparin-induced thrombocytopenia (HIT) typically occurs 5-10 days after start; check platelets regularly. Avoid intramuscular injections due to hematoma risk. Use cautiously in renal impairment (accumulation) and avoid in severe thrombocytopenia or active bleeding. For prolonged use, monitor for osteoporosis and alopecia. |
| Patient Advice | Take heparin exactly as prescribed; do not change dose or frequency without consulting your doctor. · Report any unusual bleeding, bruising, or signs of bleeding such as blood in urine/stool, coughing up blood, or heavy menstrual flow. · Notify your doctor before any surgery or dental procedure as heparin may increase bleeding risk. · Avoid aspirin, NSAIDs (ibuprofen, naproxen), and other blood thinners unless specifically prescribed by your doctor. · Use a soft toothbrush and electric razor to minimize bleeding risk; avoid contact sports or activities that may cause injury. · Inform all healthcare providers that you are taking heparin. · If you miss a dose, contact your doctor immediately; do not double the dose. |