Antiplatelet agents
Antiplatelet agents block platelet activation and aggregation to prevent arterial thrombosis. Aspirin irreversibly inhibits cyclooxygenase-1, and P2Y12 inhibitors such as clopidogrel, ticagrelor, and prasugrel block adenosine diphosphate-driven platelet activation. Aspirin 81 mg daily anchors secondary prevention, and dual antiplatelet therapy with aspirin plus a P2Y12 inhibitor is first-line after acute coronary syndrome or coronary stenting.
- Topic reviewThe full article, organized the way the exam asks it.
- ABIM-format MCQsVignettes with an explanation for every wrong answer.
- Key factsThe numbers and thresholds worth memorizing, up front.
- AI tutorMedBrain answers the question you're stuck on.
What this article covers
- Overview
What they are: antiplatelet agents block platelet activation, adhesion, or aggregation to prevent arterial thrombus, distinct from anticoagulants, which act on the coagulation cascade instead.
- Epidemiology
Population exposure: aspirin and P2Y12 inhibitors are among the most prescribed cardiovascular drugs.
- Risk factors
Bleeding risk: advanced age, female sex, anemia, low body weight, chronic kidney disease, diabetes, and concomitant glucocorticoid, NSAID, or anticoagulant use.
- Pathophysiology
Arterial hemostasis: collagen exposure triggers platelet adhesion via glycoprotein Ib binding von Willebrand factor, then activation with release of adenosine diphosphate (ADP) and thromboxane A2…
- Clinical features
Intended effect: prolonged bleeding time, not routinely measured since platelet reactivity assays have not improved outcomes when used to guide therapy.
- Differential diagnosis
Aspirin versus clopidogrel monotherapy: aspirin is preferred first-line, but clopidogrel replaces it when there is true aspirin intolerance or allergy.
- Diagnosis
Indication established by: starting an antiplatelet agent is confirmed by a defined atherothrombotic indication, acute coronary syndrome, coronary stenting, ischemic stroke or high-risk TIA, or…
- Management
First-line, aspirin: 162 to 325 mg PO load in acute coronary syndrome, then 81 mg PO daily indefinitely; low-dose aspirin (75 to 162 mg daily) matches high-dose aspirin for preventing myocardial infarction with less bleeding.
- Complications
Gastrointestinal bleeding: the most common serious complication, more frequent with DAPT than monotherapy and with concomitant NSAID or anticoagulant use.
- Prognosis
Secondary prevention benefit: aspirin lowers myocardial infarction and cardiovascular death risk in established coronary artery disease.
- Prevention
Cap ticagrelor's co-administered aspirin at 81 mg (75 to 100 mg) daily: higher aspirin doses reduce ticagrelor's efficacy, a boxed warning.
Read the whole article
Subscribing to Internal Medicine opens every article, the full question bank and MedBrain, on the web, iPhone and Android.
Related articles
- Non-ST-elevation myocardial infarction (NSTEMI)
Non-ST-elevation myocardial infarction is acute myocardial injury from partial or intermittent coronary occlusion, diagnosed by ischemic symptoms and a rising troponin without diagnostic ST elevation. Management is antiplatelet and anticoagulant therapy with risk stratification (TIMI or GRACE) guiding the timing of an invasive coronary strategy.
- ST-elevation myocardial infarction (STEMI)
ST-elevation myocardial infarction is acute transmural myocardial ischemia from complete coronary occlusion, diagnosed by ischemic symptoms with diagnostic ST-segment elevation and a rising troponin. It is a time-critical emergency in which immediate reperfusion, primary PCI within 90 minutes or fibrinolysis when PCI is unavailable, plus antiplatelet and anticoagulant therapy, determines survival.
- Ischemic stroke
Ischemic stroke is sudden focal neurologic deficit from arterial occlusion confirmed by infarction on neuroimaging. Diagnosis relies on urgent noncontrast head CT to exclude hemorrhage; treatment is IV alteplase within 4.5 hours and mechanical thrombectomy for large-vessel occlusion within an extended window, followed by antiplatelet therapy and risk-factor control.
- Atrial fibrillation
Atrial fibrillation is a supraventricular tachyarrhythmia with disorganized atrial activation and an irregularly irregular ventricular response, the most common sustained arrhythmia and a major cause of stroke. Diagnosis is by ECG showing no discrete P waves with irregular RR intervals, and management addresses rate or rhythm control, stroke prevention by CHA2DS2-VASc-guided anticoagulation, and the underlying cause.
- Anticoagulants
Anticoagulants are drugs that block steps in the coagulation cascade to prevent or treat venous thromboembolism, cardioembolic stroke, and valve thrombosis. Direct oral anticoagulants are first-line for most nonvalvular indications, while warfarin, titrated to an INR of 2 to 3, remains required for mechanical valves and high-risk antiphospholipid syndrome; parenteral heparins bridge and cover renal failure or urgent reversal needs.
- Acute upper gastrointestinal bleeding
Acute upper gastrointestinal bleeding arises proximal to the ligament of Treitz and presents with hematemesis or melena, most often from peptic ulcer disease or bleeding gastroesophageal varices. Management sequences resuscitation, restrictive transfusion, IV proton pump inhibitor therapy, and, when varices are suspected, octreotide plus antibiotic prophylaxis, all before upper endoscopy within 24 hours, which is both diagnostic and therapeutic.