Heparin vs Warfarin: aPTT vs INR, HIT, Bridging, Antidotes and DOAC Reversal

Heparin vs warfarin: two clocks 0:00

0:00 Heparin and warfarin both stop clots. They do it in different ways, on different clocks. One works in minutes through a vein. The other takes days, from a pill. Each has its own lab and its own antidote. Doses here are exam examples. Your protocol and prescriber decide the real ones.

Why anticoagulate: what blood thinners really do 0:21

0:24 Blood thinner is a nickname. These drugs don't make the blood thinner; they slow the clotting system. They stop a clot from growing and stop new ones from forming. They do not dissolve the clot that's already there. We use them for deep vein clots, pulmonary emboli, atrial fibrillation and mechanical heart valves.

Heparin: antithrombin, aPTT and anti-Xa, HIT 0:46

0:48 Heparin, the unfractionated kind, works through a natural protein in the blood called antithrombin. Heparin binds it and changes its shape, and that pair switches off thrombin and factor Xa. Given IV, it works immediately. Given under the skin, less of it reaches the blood.

1:08 And it is not given intramuscularly. Its half-life is short, about 30 minutes to 2 hours depending on the dose, so it wears off within hours. Its effect varies from patient to patient, so a heparin drip is followed with a lab. Classically that's the aPTT, often kept around 1.5 to 2.5 times control.

1:31 Some protocols use an anti-Xa level instead, often 0.3 to 0.7. The exact range depends on your lab's reagent, so follow your hospital's nomogram. The big heparin complication is HIT, heparin-induced thrombocytopenia. It's an immune reaction: platelets fall, usually 5 to 10 days after starting heparin, or sooner if the patient had heparin in the last month.

1:58 And the danger is clotting, not bleeding. So platelets are checked before heparin and regularly during it. If HIT is suspected, stop all heparin and start a non-heparin anticoagulant, such as argatroban or bivalirudin. Heparin mix-ups have caused fatal bleeding, so confirm the vial and its strength every time.

Enoxaparin (low-molecular-weight heparin) 2:21

2:24 Low-molecular-weight heparin, like enoxaparin, is heparin in shorter pieces. It acts mostly against factor Xa. It's usually given under the skin, its effect is predictable, and routine monitoring usually isn't needed. The aPTT doesn't track it; if a level is needed, it's anti-Xa.

2:45 The kidneys clear it, so the dose is adjusted when creatinine clearance is under 30. Its boxed warning is a spinal or epidural hematoma with neuraxial procedures, which can cause paralysis. HIT is less common than with heparin, but it still happens, so platelets are still watched.

Warfarin: vitamin K, INR, diet, interactions, pregnancy 3:05

3:07 Warfarin works in the liver. It blocks the enzyme that recycles vitamin K. Without that vitamin K, the liver can't finish making clotting factors II, VII, IX and X. Memory hook: 1972, backwards.

3:25 The factors already in the blood keep working until they wear out, so warfarin is slow. The INR starts to move within a day, but the peak effect takes 3 to 4 days. Warfarin is a pill, and it's followed with the PT, reported as the INR. The usual target is an INR of 2 to 3.

3:46 Some mechanical valves, such as one in the mitral position, run higher: 2.5 to 3.5. Diet matters. Vitamin K in green leafy vegetables works against warfarin. The teaching isn't "never eat greens"; it's keep vitamin K intake consistent.

4:05 Amiodarone, fluconazole and metronidazole can raise the INR. Rifampin and carbamazepine can lower it. Aspirin, NSAIDs and SSRIs add bleeding risk. And starting or stopping any antibiotic means a closer INR check.

4:22 Pregnancy: warfarin crosses the placenta and can harm the fetus. It's contraindicated, except in some patients with mechanical heart valves. For clots in pregnancy, guidelines prefer low-molecular-weight heparin.

Why heparin and warfarin overlap 4:36

4:39 So why do we overlap heparin and warfarin? First, protein C, one of the body's own anticoagulants, has a half-life of about 8 hours, so it falls early, before most clotting factors do. Second, prothrombin, factor II, lasts about 60 hours, while factor VII lasts only hours. So the INR can rise before real protection arrives.

5:05 So heparin or enoxaparin continues for at least 5 days, and until the INR has been 2 or higher for at least 24 hours.

Antidotes: protamine, vitamin K, 4-factor PCC 5:14

5:17 Antidotes. Heparin's is protamine. Protamine is a strongly basic protein: it binds heparin into a stable salt, and the anticoagulant effect is gone within about 5 minutes. Roughly 1 mg neutralizes 100 units of heparin, and it goes in slowly: no more than 50 mg over 10 minutes.

5:39 Its boxed warning is severe hypotension, cardiovascular collapse and pulmonary edema. For enoxaparin, protamine only partly works: it never fully neutralizes the anti-Xa effect. Warfarin's reversal has two parts. Vitamin K lets the liver make new factors, but that takes time: bleeding is usually controlled in 3 to 6 hours.

6:04 For major bleeding, add 4-factor PCC, prothrombin complex concentrate. It replaces factors II, VII, IX and X directly. In trials, more than half of patients had an INR of 1.3 or less 30 minutes after the infusion. They're given together: PCC works now, and vitamin K keeps it working as the replaced factors wear off.

6:30 IV vitamin K goes in slowly, no faster than 1 mg a minute, because severe reactions, even deaths, have happened during IV injection. And PCC carries its own boxed warning: blood clots.

DOACs and their reversal 6:45

6:48 The newer oral anticoagulants, the DOACs. Apixaban and rivaroxaban block factor Xa directly. Dabigatran blocks thrombin directly.

6:59 They don't need routine INR checks, and the usual clotting tests don't reliably show how much drug is on board. They're not for mechanical heart valves; that's still warfarin's job. Reversal. Dabigatran has a specific antidote, idarucizumab, 5 g IV.

7:19 For apixaban and rivaroxaban, the specific antidote, andexanet alfa, left the US market in December 2025, after a major trial linked it to more clots. In the US, 4-factor PCC is now the usual choice, used off-label. Reversal is for life-threatening or uncontrolled bleeding, or emergency surgery, not for a lab number alone.

Bleeding signs, nurses and medics 7:44

7:46 Bleeding signs to know: bleeding gums, nosebleeds, unusual bruising, red or dark brown urine, red or black tarry stools, and vomit that looks like coffee grounds. Hidden bleeding is quieter: headache, dizziness or weakness, or an unexplained drop in hematocrit or blood pressure. A retroperitoneal bleed can show up as back pain. Nurses: check the aPTT or anti-Xa, the INR and the platelets on schedule, and confirm heparin's vial and strength before you hang or titrate.

8:23 Medics: ask every patient if they take a blood thinner, which one, and when they took the last dose. External bleeding is still direct pressure, or a tourniquet when pressure fails or isn't practical. And tell the receiving team the drug's name.

Recap 8:39

8:42 Recap. Heparin: IV or under the skin, works now, aPTT or anti-Xa, watch platelets for HIT, reversed with protamine. Enoxaparin: under the skin, mostly anti-Xa, only partly reversed by protamine. Warfarin: oral and slow, INR usually 2 to 3, consistent vitamin K, reversed with vitamin K plus 4-factor PCC.

9:10 Overlap with heparin for at least 5 days and until the INR is therapeutic. DOACs: no routine INR; idarucizumab for dabigatran, PCC for the Xa blockers. ICU Basics, RN Basics and Medic Basics, available on the Apple App Store and Google Play.