Heparin
An anticoagulant that potentiates antithrombin to prevent clot formation.
The exam loves to pit heparin against warfarin and make you pick the right lab/antidote pair: heparin pairs with aPTT + protamine, while warfarin = INR + vitamin K. A reliable trap is the overlap question—patients are bridged on heparin and warfarin together for several days because warfarin’s onset is delayed (full effect takes roughly 2–5 days), so don’t flag co-administration as an error. Target an aPTT of about 1.5–2.5 times the control (commonly cited as ~45–75 seconds, though the exact range is reagent-dependent), and hold the infusion for a markedly prolonged aPTT or active bleeding. For low-molecular-weight heparin such as enoxaparin, routine aPTT monitoring is not required.
The other classic trap is the antidote: protamine sulfate is a protein, not a vitamin—students wrongly reach for vitamin K, which reverses warfarin. Heparin is also pregnancy-safe because it does not cross the placenta, whereas warfarin is teratogenic. Memory hook: “Heparin Hits the aPTT, Warfarin Works on the INR.”
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