Loading dose for mi
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Here is a complete, structured summary of loading doses used in Myocardial Infarction (MI), covering both STEMI and NSTEMI/UA, drawn from multiple authoritative sources.
Loading Doses in MI (STEMI & NSTEMI/UA)
1. ANTIPLATELET AGENTS
Aspirin (COX inhibitor)
| Setting | Loading Dose | Maintenance |
|---|---|---|
| All ACS (STEMI & NSTEMI) | 162-325 mg orally (chewed, non-enteric-coated) | 75-100 mg daily indefinitely |
- Should be given immediately to all patients with suspected acute MI.
- 325 mg preferred for aspirin-naive patients; if on ticagrelor, maintenance dose must not exceed 100 mg.
P2Y12 Inhibitors (DUAL ANTIPLATELET THERAPY - DAPT)
| Drug | Loading Dose | Maintenance | Key Notes |
|---|---|---|---|
| Clopidogrel | 300-600 mg PO | 75 mg daily | 600 mg preferred for PCI; 300 mg if given with fibrinolytics within first 24 h; NO loading dose in patients >75 years receiving fibrinolysis |
| Ticagrelor | 180 mg PO | 90 mg twice daily | Preferred P2Y12 for ACS (mortality benefit over clopidogrel in PLATO trial); reversible inhibitor |
| Prasugrel | 60 mg PO | 10 mg daily | Only after coronary anatomy known (post-angiography); contraindicated with prior stroke/TIA, age >75, weight <60 kg |
| Cangrelor | 30 mcg/kg IV bolus | 4 mcg/kg/min infusion | IV; FDA-approved for PCI only |
GPIIb/IIIa Inhibitors (mainly adjunct to PCI)
| Drug | Loading Dose | Maintenance |
|---|---|---|
| Eptifibatide | 180 mcg/kg IV bolus | 2 mcg/kg/min infusion |
| Tirofiban | 0.4 mcg/kg IV bolus | 0.1 mcg/kg/min infusion |
| Abciximab | 0.25 mg/kg IV bolus | 10 mcg/min infusion |
- Not used routinely with thrombolytics in STEMI; benefit is mainly for high-risk ACS/PCI patients.
2. ANTICOAGULANTS
| Drug | Loading Dose | Maintenance | Notes |
|---|---|---|---|
| UFH (Unfractionated Heparin) | 60 units/kg IV bolus (max 4000 units) | 12 units/kg/h (max 1000 units/h), titrate to aPTT 1.5-2.5x control | Preferred during PCI; avoid with streptokinase |
| Enoxaparin (LMWH) | 30 mg IV bolus, then 1 mg/kg SC 15 min later | 1 mg/kg SC every 12 h | Patients >75 y: NO IV bolus, reduce to 0.75 mg/kg SC bid; CrCl <30: 1 mg/kg SC once daily; creatinine cutoff: <2.5 mg/dL (men), <2 mg/dL (women) |
| Bivalirudin | 0.75 mg/kg IV bolus | 1.75 mg/kg/h infusion | Drug of choice in HIT; validated for PCI; not well-studied in thrombolysis |
| Fondaparinux | 2.5 mg IV bolus | 2.5 mg SC daily | Superior to UFH in thrombolysis with less bleeding; do NOT use as monotherapy for PCI (catheter thrombosis risk) |
3. FIBRINOLYTIC AGENTS (STEMI only - when PCI unavailable within 120 min)
| Drug | Dosing Regimen | Notes |
|---|---|---|
| Alteplase (tPA) | 15 mg IV bolus, then 0.75 mg/kg over 30 min (max 50 mg), then 0.5 mg/kg over 60 min (max 35 mg) | Weight-based; fibrin-specific |
| Tenecteplase (TNK) | Single IV bolus, weight-based (30-50 mg) | Most convenient; single bolus |
| Reteplase | 10 units IV bolus x2, 30 min apart | Double bolus |
| Streptokinase | 250,000 units IV loading dose, then 100,000 units/h for 24-72 h | Non-fibrin-specific; no repeat dosing; do NOT add UFH |
Summary: Key Mnemonics
- DAPT always = Aspirin + one P2Y12 inhibitor for minimum 12 months
- Ticagrelor > Prasugrel > Clopidogrel in potency (but bleeding risk follows the same order)
- UFH bolus = 60 units/kg (max 4000 units) - easy to remember
- Prasugrel = "wait for angio" before giving
- Patients >75 years = avoid prasugrel, avoid LMWH loading dose
Sources: Washington Manual of Medical Therapeutics, p. 139/152-153; Tintinalli's Emergency Medicine, Table 49-8/49-9; Harrison's Principles of Internal Medicine 22E, p. 2153; Katzung's Basic and Clinical Pharmacology 16E
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