Quick facts
| Feature | Heparin | Warfarin |
|---|---|---|
| Route[1][2] | IV injection, IV infusion or deep subcutaneous injection; not IM, because of hematoma risk | Oral tablet |
| Onset[1][2] | Immediate after an IV dose | Some effect within 24 hours; the peak may take 72 to 96 hours, and full effect takes several days |
| Lab to follow[1][2] | aPTT; full-dose target 1.5 to 2 times normal | INR; target 2.0 to 3.0 for venous clots and nonvalvular atrial fibrillation |
| Reversal[1][2] | Protamine sulfate | Vitamin K1; concentrates or plasma may be considered if urgent |
| Watch for[1][2] | Heparin-induced thrombocytopenia (HIT): stop and evaluate if platelets fall below 100,000/mm3 or a new clot forms | Many drug, herbal and vitamin K food interactions; skin necrosis |
| Clot already formed[1][2] | Doesn't dissolve it | No direct effect on it |
| Shared risk[1][2] | Bleeding, including fatal hemorrhage | Major or fatal bleeding (boxed warning) |
| ISMP high-alert[3] | Yes | Yes |
Before either drug: check for bleeding and review the right labs
- Before giving either drug, look for bleeding (bruises on the arms or legs, blood in the urine or stool) and review the coagulation labs and platelets.[4]
- Report new bleeding right away, along with a falling blood pressure and rising heart rate, which can signal internal bleeding.[4]
- NSAIDs, aspirin and other platelet inhibitors add to the bleeding risk with both drugs.[1][2]
- Both are on ISMP's high-alert medication list.[3]
Heparin: follow the aPTT, the platelet count and the product strength
- For full-dose IV heparin, the label targets an aPTT 1.5 to 2 times normal and follows it about every 4 hours at the start.[1]
- Patients getting subcutaneous heparin to prevent DVT don't need aPTT monitoring.[4]
- Get a platelet count before therapy and periodically during it. If it falls below 100,000/mm3 or a new clot forms, heparin is stopped and HIT is evaluated.[1]
- HIT can appear up to several weeks after heparin is stopped.[1]
- Confirm the product and strength before giving it: mix-ups with catheter lock flush vials have caused fatal bleeding in children.[1]
- Bleeding is more common in patients over 60, especially women.[1]
Warfarin: follow the INR and any change in drugs or diet
During the overlap, heparin covers the patient until the INR reaches the target
- Warfarin's full effect takes several days, so heparin is used for fast anticoagulation. The label overlaps the two for 4 to 5 days and until the INR shows the desired response, then heparin is stopped.[1][2]
- Heparin can raise the INR, so during the overlap the INR is drawn at least 5 hours after an IV bolus, 4 hours after a continuous infusion stops, or 24 hours after a subcutaneous dose.[2]
Teach bleeding precautions for both drugs
- Use an electric razor. For heparin, Open RN adds a soft toothbrush and no IM injections.[4]
- Avoid aspirin and NSAIDs unless the prescriber says otherwise.[2][4]
- Tell every provider and dentist about the anticoagulant before surgery or a procedure.[1][2]
- Report any unusual bleeding or bruising right away.[1][2]
Practice warfarin INR, bleeding, and diet questions in the Antiplatelet and anticoagulant reasoning flashcard deck.
Browse flashcardsHow it shows up on nursing exams
- Heparin is followed with the aPTT and warfarin with PT/INR.[1][2]
- Protamine sulfate reverses heparin, and vitamin K reverses warfarin.[1][2]
- They overlap because warfarin is slow: heparin covers the patient until the INR is therapeutic.[2]
- A platelet count below 100,000/mm3 on heparin means stopping it and evaluating for HIT.[1]
Practice question
A 61-year-old patient with a new deep vein thrombosis is on a continuous IV heparin infusion on the medical-surgical unit and started warfarin yesterday. This morning the INR is 1.3 and the aPTT is in the target range. The patient asks, "Why do I need two blood thinners?" Which response by the nurse is accurate?
- A. "Heparin helps your stomach absorb the warfarin tablets so they work better"
- B. "Both drugs keep your aPTT in range, which dissolves the clot in your leg faster"
- C. "You will keep taking both of these drugs for as long as your INR needs checking"
- D. "Warfarin is slow to work, so heparin protects you until your INR is in range"
Show the answer and why
Correct answer: D. "Warfarin is slow to work, so heparin protects you until your INR is in range"
- A. Incorrect. Heparin isn't given to help warfarin absorb. It anticoagulates right away while warfarin is still building its effect.
- B. Incorrect. Heparin is the drug followed with the aPTT, and neither drug breaks down a clot that has already formed: heparin has no fibrinolytic activity, and warfarin doesn't act directly on a clot that's already there.
- C. Incorrect. The overlap is temporary. After at least 4 to 5 days, once the INR shows the desired response, heparin is stopped, and INR checks go on while the patient takes warfarin alone.
- D. Correct. Warfarin's full effect takes several days, so the label overlaps it with full-dose heparin for 4 to 5 days and until the INR shows the desired response. An INR of 1.3 is still below the 2.0 to 3.0 target for venous clots.
Sources for this question: [1][2]
Memory hook: Heparin hits fast (aPTT, protamine); warfarin waits (INR, vitamin K).