Antithrombotics compared — anticoagulants, antiplatelets and thrombolytics
Verified · Oct 2026Antiplatelets act on the platelet plug, anticoagulants on the coagulation cascade, and thrombolytics on the fibrin clot that already exists. Where a drug acts decides which test tracks it and which agent, if any, reverses it.
Three stages, three drug families
Platelets adhere through von Willebrand factor binding GP Ib-IX, then release ADP and thromboxane A₂, which recruit more platelets. Arterial thrombi form on ruptured plaque and are platelet-rich, so antiplatelet drugs are the cornerstone there; venous thrombi form in stasis and are fibrin-rich.
In the coagulation cascade, the extrinsic (tissue factor–VIIa) and intrinsic pathways converge on factor Xa, which converts prothrombin to thrombin; thrombin converts fibrinogen to fibrin. The PT tracks the extrinsic pathway and the PTT the intrinsic. Anticoagulants act here — on antithrombin, factor Xa, thrombin or vitamin K–dependent factor synthesis — and prevent new clot rather than dissolving it.
Fibrinolysis removes clot: plasminogen bound to fibrin is converted to plasmin, which breaks down the fibrin mesh. Thrombolytics are recombinant tissue plasminogen activators that drive this step.
Comparison
The drugs compared
| Agent | Target | Monitoring test | Reversal agent | Bleeding-risk features | Other signature effect |
|---|---|---|---|---|---|
| Unfractionated heparin | Binds antithrombin → inactivates thrombin and factor Xa | aPTT | Protamine | Uncontrolled active bleeding contraindicated; aspirin, NSAIDs and other antiplatelets add bleeding | Heparin-induced thrombocytopenia; osteoporosis with chronic use, hyperkalemia |
| Enoxaparin (LMWH) | Antithrombin-mediated, with more anti-Xa than anti-thrombin activity | No routine lab monitoring (anti-Xa levels may be used in renal impairment) | Protamine — partial reversal | Boxed spinal/epidural hematoma with neuraxial anesthesia; dose adjusted when creatinine clearance is below 30 mL/min | Lower HIT risk than unfractionated heparin |
| Fondaparinux | Antithrombin-mediated selective factor Xa inhibition | PT and aPTT are insensitive | — | Renally eliminated; contraindicated with creatinine clearance below 30 mL/min | Does not cause HIT or react with HIT antibodies |
| Warfarin | Inhibits VKORC1 → factors II, VII, IX, X (and proteins C, S) not carboxylated | INR | Vitamin K; 4-factor prothrombin complex concentrate for serious bleeding | Boxed major or fatal bleeding; potentiated by CYP2C9 inhibitors, some antimicrobials and amiodarone; consistent vitamin K intake | Skin necrosis from early protein C loss; embryopathy (contraindicated in pregnancy) |
| Apixaban, rivaroxaban, edoxaban | Factor Xa, directly | No routine lab monitoring | Andexanet alfa (labeled for rivaroxaban and apixaban) | Boxed spinal/epidural hematoma; premature discontinuation raises thrombotic events; not for mechanical valves | Edoxaban: more ischemic stroke with creatinine clearance above 95 mL/min in atrial fibrillation |
| Dabigatran | Thrombin, directly (prodrug converted by esterases) | No routine lab monitoring | Idarucizumab | Mainly renally cleared; contraindicated with mechanical heart valves; removable by hemodialysis | GI reactions (dyspepsia, gastritis-like symptoms) |
| Argatroban, bivalirudin | Thrombin, directly and reversibly (IV) | aPTT (argatroban); ACT (bivalirudin) | No antidote | Argatroban is hepatically cleared — slower reversal in hepatic impairment | Used for heparin-induced thrombocytopenia |
| Aspirin | COX-1, irreversibly (acetylation) → less thromboxane A₂ | Not generally required | — | Effect lasts the platelet lifespan, 7–10 days; GI bleeding | Reye syndrome in children and teenagers with chickenpox or flu-like illness; bronchospasm in aspirin-exacerbated respiratory disease |
| P2Y12 inhibitors | ADP P2Y12 receptor — clopidogrel and prasugrel irreversibly (active metabolites), ticagrelor reversibly | Not generally required | — | Boxed significant, sometimes fatal bleeding (prasugrel, ticagrelor); stop clopidogrel or ticagrelor at least 5 days and prasugrel at least 7 days before major surgery | Clopidogrel loses effect in CYP2C19 poor metabolizers (boxed); ticagrelor dyspnea; prasugrel contraindicated after TIA or stroke |
| Eptifibatide, tirofiban | GP IIb/IIIa — block fibrinogen and von Willebrand factor binding (reversible, IV) | Platelet count within hours of starting | — | Bleeding mostly at the arterial access site; platelet function recovers within hours of stopping eptifibatide | Acute, profound thrombocytopenia |
| Alteplase, tenecteplase | Convert fibrin-bound plasminogen to plasmin | Fibrinogen falls; coagulation tests can be unreliable in vitro | No antidote — stop the drug; cryoprecipitate commonly used to restore fibrinogen in intracranial hemorrhage | Intracranial hemorrhage the greatest concern (head CT before use); puncture-site bleeding | Angioedema (more with ACE inhibitors); reperfusion arrhythmias |
High-yield
Practice questions
Q1On day 6 of a heparin infusion after cardiac surgery, a 63-year-old man’s platelets have halved and an anti-PF4/heparin antibody assay is positive. He still needs anticoagulation.
Which anticoagulant is appropriate now?
- A.Enoxaparin
- B.Argatroban
- C.Warfarin alone
- D.Aspirin
- E.Alteplase
Show answer
B. Argatroban — In heparin-induced thrombocytopenia all heparin, including flushes, is stopped and an alternative anticoagulant such as argatroban, bivalirudin or fondaparinux is used; argatroban and bivalirudin are short-acting, and bivalirudin is usually reserved for cardiac catheterization or cardiac surgery. Warfarin is risky in the acute phase and is held, and fondaparinux does not react with heparin-induced antibodies.
Q2A 74-year-old man taking apixaban for atrial fibrillation presents with massive hematemesis and hypotension.
Which agent specifically reverses his anticoagulant?
- A.Protamine sulfate
- B.Vitamin K
- C.Idarucizumab
- D.Aminocaproic acid
- E.Andexanet alfa
Show answer
E. Andexanet alfa — Andexanet alfa is labeled for patients treated with rivaroxaban or apixaban who need reversal for life-threatening or uncontrolled bleeding. Idarucizumab reverses dabigatran, protamine reverses heparin, and vitamin K (with prothrombin complex concentrate for serious bleeding) reverses warfarin. Aminocaproic acid is an antifibrinolytic for bleeding from elevated fibrinolytic activity, not a specific reversal agent.
Q3A 66-year-old man with an acute pulmonary embolism starts an intravenous anticoagulant whose dose is adjusted to a clotting test drawn every 6 hours until it is in range.
Which drug–test pair fits?
- A.Unfractionated heparin — aPTT
- B.Warfarin — aPTT
- C.Apixaban — INR
- D.Enoxaparin — INR
- E.Fondaparinux — aPTT
Show answer
A. Unfractionated heparin — aPTT — Intravenous heparin is adjusted to the aPTT, checked at baseline and every 6 hours until therapeutic; the PTT tracks the intrinsic pathway and the PT the extrinsic. Warfarin is an oral drug monitored with regular INR checks, and the direct oral anticoagulants were designed to need no routine laboratory monitoring. The PT and aPTT are relatively insensitive measures of fondaparinux activity.
Q4A 64-year-old man with a non-ST-elevation myocardial infarction is scheduled for PCI. He had a transient ischemic attack two years ago.
Which P2Y12 inhibitor is contraindicated for him?
- A.Clopidogrel
- B.Ticagrelor
- C.Prasugrel
- D.Cangrelor
- E.None of the P2Y12 inhibitors
Show answer
C. Prasugrel — Prasugrel is contraindicated in patients with a prior transient ischemic attack or stroke, and it is generally not recommended at 75 years or older. Active pathological bleeding contraindicates clopidogrel, and a history of intracranial hemorrhage contraindicates ticagrelor — neither applies here. Cangrelor’s only contraindications are significant active bleeding and hypersensitivity to the product, so a prior TIA is not one of them.
Sources
- Nursing Pharmacology 2e, Ch. 6 — anticoagulants — Open RN (NCBI Bookshelf)
- JANTOVEN (warfarin) — FDA label — FDA / DailyMed
- ACTIVASE (alteplase) — FDA label — FDA / DailyMed
- Argatroban injection — FDA label — FDA / DailyMed
- BRILINTA (ticagrelor) — FDA label — FDA / DailyMed
- Physiology, Coagulation Pathways — StatPearls (NCBI)
- Eptifibatide injection — FDA label — FDA / DailyMed
- AGGRASTAT (tirofiban) — FDA label — FDA / DailyMed
- ARIXTRA (fondaparinux) — FDA label — FDA / DailyMed
- Warfarin Toxicity — StatPearls (NCBI)
- Heparin-Induced Thrombocytopenia — StatPearls (NCBI)
- PRADAXA (dabigatran) capsules — FDA label — FDA / DailyMed
- ELIQUIS (apixaban) — FDA label — FDA / DailyMed
- Salicylic Acid (Aspirin) — StatPearls (NCBI)
- Aminocaproic Acid — StatPearls (NCBI)
- Tenecteplase — StatPearls (NCBI)
- Heparin — StatPearls (NCBI)
- Enoxaparin — StatPearls (NCBI)
- Bivalirudin for injection — FDA label — FDA / DailyMed
- ANDEXXA (andexanet alfa) — FDA label — FDA / DailyMed
- Physiology, Hemostasis — StatPearls (NCBI)
- PLAVIX (clopidogrel) — FDA label — FDA / DailyMed
- EFFIENT (prasugrel) — FDA label — FDA / DailyMed
- Antiplatelet Medications — StatPearls (NCBI)
- Hypercoagulability — StatPearls (NCBI)
- ECOTRIN aspirin — FDA label — FDA / DailyMed
- Acute Stroke: Evaluation and Management — StatPearls (NCBI)
- Tranexamic Acid — StatPearls (NCBI)
- KENGREAL (cangrelor) — FDA label — FDA / DailyMed
- The use of stems in the selection of INN (stems -entan, -afil, -ciguat, prost) — World Health Organization
- Vitamin K — γ-carboxylation and the vitamin K cycle — StatPearls (NCBI)
- Xarelto (rivaroxaban) — FDA label: pharmacokinetics, food — FDA / DailyMed
- Clopidogrel — activation pathway, half-lives — StatPearls (NCBI)
- Glycoprotein IIb/IIIa Inhibitors — mechanism, IV-only agents — StatPearls (NCBI)
- Alteplase — plasmin lyses fibrin and fibrinogen; half-lives — StatPearls (NCBI)
- Heparin sodium injection — FDA label — FDA / DailyMed
- Praxbind (idarucizumab) — FDA label: antibody fragment binding dabigatran — FDA / DailyMed
- Thrombosis — arterial vs venous thrombosis — StatPearls (NCBI)
- Protamine — cationic salt with heparin, partial LMWH reversal — StatPearls (NCBI)
- Physiology, Thromboxane A2 — COX-1, TP receptor, GP IIb/IIIa activation — StatPearls (NCBI)
- StatPearls: Anterior Myocardial Infarction — StatPearls (NCBI)
- TNKASE (tenecteplase) — structure, fibrin specificity, pharmacokinetics, AcT and ASSENT trials (FDA label) — FDA / DailyMed
- Lovenox (enoxaparin) — FDA label: renal impairment, anti-Xa — FDA / DailyMed
- Warfarin — VKORC1, CYP2C9, onset, skin necrosis — StatPearls (NCBI)
- Warfarin Drug Interactions — antimicrobials, amiodarone — StatPearls (NCBI)
- Deep Venous Thrombosis — LMWH in pregnancy — StatPearls (NCBI)
- Savaysa (edoxaban) — FDA label: CrCl > 95 box, pharmacokinetics — FDA / DailyMed
- Bayer Aspirin Regimen (aspirin) — drug facts — DailyMed (NLM)
- Eptifibatide — platelet recovery, thrombocytopenia — StatPearls (NCBI)
- StatPearls: Virchow Triad — StatPearls (NCBI)
Each class page compared lists its full sources; this page reuses facts verified there.
By LearnDrugs
Educational summary for medical students. Always verify against current prescribing information and guidelines. Not medical advice.