Heparin (Unfractionated)

Emergency & Prehospital

• STEMI and NSTE-ACS: heparin runs alongside antiplatelet therapy, PCI or fibrinolysis. Prehospital bolus only where protocol allows. Reach for enoxaparin or fondaparinux when no early invasive approach is planned. Enoxaparin is the recommended agent after fibrinolysis without planned invasive care. Bivalirudin is for STEMI PCI.
• Interfacility transfer on a running infusion: PE, ACS, arterial thrombosis or mechanical circulatory support

ED / ICU / Transport

• Acute PE and DVT: Pick heparin when rapid offset or reversal matters (thrombolysis or a procedure anticipated, CrCl <30 mL/min, high bleeding risk, possible ECMO). LMWH is preferred for most hospitalized PE.
• PCI and cardiac catheterization: procedural anticoagulation titrated to the activated clotting time (ACT)
• Extracorporeal circuits: ECMO, Impella, CRRT, hemodialysis and cardiopulmonary bypass
• Atrial fibrillation: heparin prevents and treats thromboembolic complications when parenteral anticoagulation is needed. Don't bridge with heparin when warfarin is interrupted for an elective procedure in AF. The BRIDGE trial makes the case. Arterial thromboembolism was 0.4% without bridging and 0.3% with LMWH bridging. Major bleeding was 1.3% without bridging and 3.2% with it (RR 0.41). ACCP 2022 gives a strong recommendation against heparin bridging in AF.
• Mechanical heart valves, or AF with a recent stroke or TIA: bridging may be needed when warfarin is interrupted; individualized per valve guideline
• Acute arterial embolism: acute limb ischemia pending revascularization

Other Uses

• VTE prophylaxis: medical and surgical patients, especially with severe renal impairment
• DIC with thrombosis: labeled for consumption coagulopathy; specialist use only
• Catheter patency: low-concentration lock-flush products only, never therapeutic vials

Available Forms

• Vials: 1,000 units/mL (2 mL preservative-free; 10 mL and 30 mL multiple-dose), 5,000 units/mL and 10,000 units/mL; multiple-dose vials contain benzyl alcohol
• Premixed bags: 25,000 units in 250 mL (100 units/mL), 25,000 units in 500 mL (50 units/mL) or 20,000 units in 500 mL (40 units/mL) in D5W; read total units and volume on every bag
• Flush products: 2 units/mL in 0.9% sodium chloride (arterial lines); heparin lock flush 10 or 100 units/mL for catheter locks only

Adult Dosing

Pediatric Dosing

Administration

• Bolus and infusion: IV push from a verified vial or the pump bolus function; premixed bags preferred; an admixture expires after 4 hr at room temperature or 24 hr refrigerated
• Line: never IM (hematoma); never draw coagulation tests from the heparin line

Switching Anticoagulants

• UFH to DOAC: give the first apixaban, rivaroxaban or dabigatran dose and stop the infusion at the same time; edoxaban starts 4 hr after the infusion stops
• UFH to LMWH or warfarin: first enoxaparin dose when the infusion stops; warfarin overlaps at least 5 days until the INR is therapeutic; draw the INR at least 5 hr after the last IV heparin dose (24 hr after a subcut dose)
• DOAC or LMWH to UFH: start when the next dose would have been due, usually without a bolus; monitor by aPTT

Contraindications

• Uncontrollable active bleeding, unless caused by DIC
• History of HIT or HIT with thrombosis (exception: remote HIT needing cardiac surgery, hematology-directed)
• Prior thrombocytopenia with pentosan polysulfate; hypersensitivity to heparin or pork products
• Full-dose therapy where coagulation monitoring is unavailable

Precautions

• Bleeding risk: recent brain, spine or eye surgery, GI ulceration, severe hypertension, endocarditis, liver or severe renal disease, severe thrombocytopenia (a labeled contraindication on some premixed bags; heparin is often still needed, e.g. in DIC or on ECMO)
• Neuraxial anesthesia: time punctures and catheter removal around doses per ASRA guidance (spinal epidural hematoma)
• Age over 60, especially women: higher bleeding incidence
• Heparin resistance: fever, infection, thrombosis, MI, cancer, after surgery, antithrombin deficiency

Hold / Reassess If

• New bleeding, Hgb drop ≥2 g/dL, hypotension or neuro change: stop, notify, STAT CBC and anti-Xa/aPTT
• Platelets fall >50% or below 100,000/mm³, or new thrombosis: score the 4Ts; level above range: hold and reduce per nomogram

• Common: minor bleeding (bruising, line oozing, epistaxis); subcut injection-site hematoma; transaminase elevation; hypersensitivity (chills, fever, urticaria); long-term high-dose osteoporosis and alopecia
• Thrombocytopenia hits up to 30% (onset 2–20 days). An early, mild, non-immune dip recovers on heparin. Still, score any fall with the 4Ts.

Serious / Life-Threatening

HIT: 4Ts Score

1. Low (0–3): HIT very unlikely; do not test or treat empirically.
2. Intermediate (4–5) or high (6–8): stop all heparin; start a therapeutic non-heparin anticoagulant (therapeutic intensity unless bleeding risk is high for intermediate); send a PF4/heparin immunoassay, then a functional assay (serotonin release) if positive. Negative immunoassay: stop the non-heparin agent and resume heparin if indicated.
3. Confirmed HIT: no routine platelet transfusion; no warfarin until platelets ≥150,000/mm³ (if already on warfarin, stop it and give IV vitamin K); agents: argatroban, bivalirudin, fondaparinux or a DOAC.

Overdose & Toxicity Management

• No bleeding: hold the infusion and restart lower per nomogram; effect fades within hours (half-life 0.5–2 hr)
• Bleeding: protamine 1 mg slow IV per 100 units of heparin still circulating; after a bolus assume a 30-min half-life; for infusions count the heparin given over the last 2–3 hr; max 50 mg per dose, no faster than 50 mg in 10 min; same ratio in children (max 50 mg); recheck aPTT or ACT
• Protamine risks: hypotension, bradycardia, pulmonary hypertension, anaphylaxis (prior protamine or NPH insulin, fish allergy, vasectomy)
• Ineffective: Don't reach for vitamin K or PCC. Neither reverses heparin. Andexanet is not a heparin antidote.

• Anti-Xa vs aPTT: Titrate to anti-Xa when it is reliable. That means critical illness, a prolonged baseline aPTT, heparin resistance or ECMO. A recent DOAC or LMWH makes anti-Xa read falsely high. The aPTT misreads with lupus anticoagulant, DOACs, warfarin, high factor VIII or fibrinogen (see the aPTT page).
• Discordant results: A high aPTT with a low anti-Xa points to factor deficiency. It does not mean too much heparin.
• ECMO and Impella: targets on the ECMO page; Impella purge heparin counts toward the total

Clinically Significant Interactions

IV Compatibility

• Diluents: 0.9% sodium chloride or D5W; incompatible (label examples): alteplase, amikacin, gentamicin, tobramycin, ciprofloxacin, droperidol, promethazine
• Line: dedicated line or verified Y-site; verify with an institutional compatibility resource

• Pediatrics: Anti-Xa is preferred. Antithrombin and baseline aPTT both vary with age. See the Pediatric Dosing table and weight-based dosing.
• Neonates: Preservative-free products only, because of benzyl alcohol gasping syndrome. The half-life is about 35 min, so requirements run higher.
• Pregnancy: Published reports show no increase in adverse maternal or fetal outcomes. LMWH is usually preferred. UFH suits the peripartum period when neuraxial anesthesia or rapid reversal is planned. Preservative-free product recommended (label).
• Lactation: Heparin is a large molecule. It isn't expected in milk, and the infant doesn't absorb it orally. It is compatible with breastfeeding. Preservative-free product recommended (label).
• Older Adults: Over 60, and especially women, means higher heparin levels, a higher aPTT and more bleeding. Lower doses may be needed.
• Renal Impairment: When CrCl is <30 mL/min, UFH is preferred over LMWH. No dose adjustment is needed.
• Hepatic Impairment: No specific adjustment. Low antithrombin and a prolonged baseline aPTT muddy the monitoring. Use anti-Xa.
• Obesity / Dosing Weight: Most VTE nomograms dose on actual body weight. Many cap the bolus or the rate.
• Prior HIT: Avoid all heparin. That includes flushes, coated catheters and purge solutions.

• Scope: RN and critical-care transport manage infusions. A paramedic's STEMI bolus or infusion monitoring varies by state and agency protocol.
• Storage & Stability: vials at 20–25°C (68–77°F); premixed bags at room temperature, away from vehicle heat; an admixed bag expires 4 hr after mixing.
• Carried Concentration: confirm the bag concentration (commonly 40, 50 or 100 units/mL) and convert to units/kg/hr, not only mL/hr; never draw a bolus from a flush supply.
• Infusions in Transport: Run the pump with the drug library and a dedicated line. Carry enough volume for the trip plus a delay. On ECMO or Impella, track circuit heparin and purge heparin separately.
• Handoff Essentials: indication, weight, bolus dose and time, current rate (units/kg/hr and mL/hr), bag concentration, last anti-Xa or aPTT and next draw due, platelet trend, HIT status, sheath status.

Mechanism of Action

• Binding a pentasaccharide sequence to antithrombin speeds its inactivation of thrombin (IIa) and factor Xa about 1,000-fold.
• Chains of 18 or more saccharides bridge antithrombin to thrombin. That is how UFH inhibits IIa and Xa, while LMWH acts mostly on Xa.
• Heparin binds plasma proteins, endothelium and platelet factor 4. The result is a variable dose response (lab titration). The same PF4 binding forms the PF4/heparin antigen of HIT.

Pharmacokinetics

• Half-life: 0.5–2 hr, and it depends on dose. In neonates it is about 35 min.
• Metabolism and elimination: There is no enzymatic degradation. Uptake is rapid and saturable, then renal clearance is slower. It accumulates less than LMWH in renal failure.
• Distribution: Vd is about 0.07 L/kg, mostly intravascular. Subcut bioavailability is low and dose-dependent.

Generic Name

Heparin sodium (unfractionated heparin, UFH), from porcine intestinal mucosa

Brand Names

Generic only in the US (multiple manufacturers); premixed heparin in D5W or 0.9% sodium chloride; separate heparin lock flush products

Pharmacologic Class

Unfractionated heparin; antithrombin-dependent indirect thrombin and factor Xa inhibitor

Therapeutic Class

Parenteral anticoagulant

Controlled Substance

Not controlled

ISMP High-Alert

Yes: ISMP high-alert medication (antithrombotic agents, including IV unfractionated heparin)

Look-Alike / Sound-Alike

heparin / Hespan (hetastarch); heparin vial strengths with each other and with heparin lock flush; heparin / insulin (both dosed in units)

Error-Prone Abbreviations to Avoid

“U” or “IU” for units (misread as 0, 4 or IV)