Case 8: A 75-year-old patient complained of compressive, pressing chest pains lasting more than 1 hour, lack of air, and severe weakness. On examination: the condition is severe, the skin is cold, covered with sticky sweat, cyanosis. There are scattered dry wheezes in the lungs, wet wheezes in the lower segments of the lungs. Blood pressure-90/60 mmHg, heart rate-98 per minute. On the ECG: ST segment elevation on the anterolateral wall of the left ventricle. Choose a drug for the prevention of thrombosis Station 1 1. Identify the problem (diagnosis): 2. Choose your P-medication for this condition: 3. Dosage form 4. Dosage Station 2 5. Pharmacokinetics of the drug 6. Mechanism of action 7. Write a prescription Station 3 8. Duration of treatment 9. Side effects 10. Contraindications
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Based on the clinical presentation and textbook sources, here is a complete answer to all stations:
Case Analysis: STEMI with Cardiogenic Shock
Station 1
1. Diagnosis
ST-elevation myocardial infarction (STEMI) of the anterolateral wall of the left ventricle, complicated by acute left ventricular failure (Killip class III–IV / cardiogenic shock).
Clinical reasoning:
- Compressive chest pain >1 hour — classic ischemic presentation
- ECG: ST elevation in anterolateral leads (I, aVL, V1–V6)
- Cold, clammy skin, cyanosis, BP 90/60 mmHg → cardiogenic shock
- Wet rales in lower lung segments → acute pulmonary edema
2. P-drug (Drug of Choice for Prevention of Thrombosis)
Unfractionated Heparin (UFH) — or its LMWH equivalent Enoxaparin (Low-Molecular-Weight Heparin)
In STEMI, anticoagulation with heparin is the cornerstone of antithrombotic therapy to:
- Prevent propagation of coronary thrombus
- Prevent re-occlusion after thrombolysis or PCI
- Prevent mural thrombus formation and systemic embolism
"Heparin is indicated for prevention and treatment of venous thromboembolic disease, arterial thrombosis, and prevention of thrombosis in arterial or cardiac surgery." — Katzung's Basic and Clinical Pharmacology, 16th Ed., p. 959
3. Dosage Form
- Unfractionated Heparin (UFH): Solution for injection (5,000 IU/mL) — administered IV bolus + continuous IV infusion
- Enoxaparin (LMWH): Solution for SC injection (100 mg/mL, pre-filled syringe)
4. Dosage
- UFH: IV bolus 60–70 IU/kg (max 5,000 IU), then continuous IV infusion 12–15 IU/kg/hour (max 1,000 IU/hour), titrated to aPTT 50–75 seconds (1.5–2.5× control)
- Enoxaparin (LMWH): 1 mg/kg SC every 12 hours (reduce to 1 mg/kg once daily if CrCl <30 mL/min); in STEMI with thrombolysis: 30 mg IV bolus, then 1 mg/kg SC q12h
Station 2
5. Pharmacokinetics
| Property | UFH | LMWH (Enoxaparin) |
|---|---|---|
| Route | IV or SC | SC (or IV) |
| Bioavailability (SC) | ~30% (variable) | ~90% (predictable) |
| Onset | Immediate (IV) | 1–3 h (SC) |
| Half-life | 30 min – 2 hours (dose-dependent) | ~4–5 hours |
| Elimination | Saturable protein binding + dose-dependent; hepatic/reticuloendothelial | Primarily renal |
| Monitoring | aPTT required | Not routinely required (predictable kinetics) |
| Antidote | Protamine sulfate (1 mg per 100 IU UFH) | Protamine (partially reverses ~60%) |
"The elimination of heparin is complex, with the saturable protein binding phase followed by dose-dependent elimination with a half-life of 30 minutes to 2 hours." — Katzung's Basic and Clinical Pharmacology, 16th Ed., p. 959
"LMW heparins—in comparison with UFH—have equal efficacy, increased bioavailability from the subcutaneous site of injection, and less frequent dosing requirements." — Katzung's Basic and Clinical Pharmacology, 16th Ed.
6. Mechanism of Action
Heparin is an indirect thrombin inhibitor that acts by binding to antithrombin III (AT-III):
- Heparin binds AT-III via a specific pentasaccharide sequence, causing a conformational change in AT-III that dramatically accelerates its inhibitory activity (~1000-fold)
- The heparin–AT-III complex inhibits thrombin (factor IIa), factor Xa, and (to a lesser extent) factors IXa, XIa, and XIIa
- UFH inhibits both thrombin and factor Xa (requires chains >18 saccharides to bridge thrombin and AT-III)
- LMWH predominantly inhibits factor Xa (short chains can bind AT-III but not thrombin simultaneously)
Net result: Interruption of the coagulation cascade → prevention of fibrin clot propagation
7. Prescription
Rp:
Sol. Heparini 5,000 IU/mL — 5 mL (25,000 IU)
D.t.d. No. 5 in amp.
S. IV bolus 5,000 IU stat, then 1,000 IU/hour continuous IV infusion
(Monitor aPTT every 6 hours, target 50–75 sec)
— or —
Rp:
Sol. Enoxaparini natrii 100 mg/mL — 0.6 mL (60 mg)
D.t.d. No. 14 in syringae preimpletae
S. 1 mg/kg SC every 12 hours
Station 3
8. Duration of Treatment
- Acute phase (in-hospital): UFH for 48–72 hours minimum in STEMI (or until PCI/revascularization)
- LMWH: Typically 5–8 days or until discharge from acute care
- Followed by long-term antiplatelet therapy (aspirin ± clopidogrel/ticagrelor) and/or oral anticoagulants if indicated (e.g., for mural thrombus, atrial fibrillation)
9. Side Effects
| Side Effect | Details |
|---|---|
| Bleeding | Most common and serious; risk increased in elderly women, renal failure patients |
| Heparin-Induced Thrombocytopenia (HIT) | Occurs in 1–4% with UFH; immune-mediated platelet activation → paradoxical thrombosis |
| Osteoporosis | With long-term use (>3 months); spontaneous fractures |
| Alopecia | Reversible hair loss |
| Hypoaldosteronism | Mineralocorticoid deficiency with long-term use |
| Hyperlipidemia clearing | Releases lipoprotein lipase; postprandial lipemia |
| Hypersensitivity | Heparin is of animal origin; allergic reactions possible |
"The major adverse effect of heparin is bleeding... Elderly women and patients with renal failure are more prone to hemorrhage." — Katzung's Basic and Clinical Pharmacology, 16th Ed.
10. Contraindications
| Contraindication | Category |
|---|---|
| Active major bleeding (intracranial, GI) | Absolute |
| Thrombocytopenia or known HIT | Absolute |
| Hypersensitivity to heparin | Absolute |
| Hemophilia or other clotting disorders | Absolute |
| Severe uncontrolled hypertension | Relative |
| Recent neurosurgery / ocular surgery / spinal puncture | Relative |
| Bacterial endocarditis | Relative |
| Severe hepatic insufficiency | Relative |
| Threatened abortion | Relative |
| Intramuscular injections (IM route is contraindicated for heparin itself) | Route-specific |
Summary: This patient has STEMI with cardiogenic shock. The drug of choice for thrombosis prevention is Heparin (UFH or LMWH/Enoxaparin), acting through AT-III–mediated inhibition of thrombin and factor Xa, administered IV/SC with aPTT monitoring, with primary risks of bleeding and HIT requiring close surveillance.
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