What is the recommended dose of Unfractionated Heparin (UFH) in acute myocardial infarction?

UFH Dosing in Acute Myocardial Infarction

For acute myocardial infarction, administer unfractionated heparin as a weight-based bolus of 60 U/kg (maximum 4,000 U) followed by an infusion of 12 U/kg/hour (maximum 1,000 U/hour), adjusted to maintain aPTT at 1.5-2.0 times control (50-70 seconds). 1

Dosing by Clinical Scenario

STEMI with Fibrinolytic Therapy

• Administer an initial bolus of 60 U/kg IV (maximum 4,000 U) followed by 12 U/kg/hour infusion (maximum 1,000 U/hour). 1, 2
• Target aPTT should be maintained at 1.5-2.0 times control, approximately 50-70 seconds. 2, 3
• Continue the infusion for 48 hours, then discontinue unless the patient has high risk for systemic or venous thromboembolism. 2, 3
• Check aPTT at 3,6,12, and 24 hours after initiation, then 4-6 hours after any dose adjustment. 2, 3

NSTE-ACS/Unstable Angina

• Administer an initial bolus of 60-70 U/kg (maximum 5,000 U) followed by 12-15 U/kg/hour infusion (maximum 1,000 U/hour). 1, 4
• Target the same aPTT range of 50-70 seconds. 4

Primary PCI Without Prior Anticoagulation

• For patients undergoing primary PCI who have not received prior anticoagulant therapy, give 70-100 U/kg IV bolus to achieve target ACT of 250-300 seconds. 1, 3
• When used with glycoprotein IIb/IIIa inhibitors, reduce the bolus to 60 U/kg (maximum 4,000 U) and target ACT of 200-250 seconds. 3

Primary PCI With Prior UFH

• In patients already receiving UFH who proceed to PCI, administer additional UFH as needed to achieve ACT 250-300 seconds rather than restarting the full regimen. 1, 2

Critical Dosing Caveats

Never exceed the maximum dose caps of 4,000 U bolus or 1,000 U/hour initial infusion, as exceeding these limits significantly increases bleeding risk. 2, 5

• Weight-based dosing is essential because body weight is the strongest predictor of heparin effect on aPTT; fixed-dose regimens result in suboptimal anticoagulation in heavier patients and excessive anticoagulation in lighter patients. 2, 5
• Excess weight-adjusted dosing occurs in approximately 35% of cases and is most common in elderly patients and females due to lower body weight. 5
• The risk of major bleeding increases proportionally when UFH doses exceed 70 U/kg for bolus or 15 U/kg/hour for infusion. 5

Monitoring Requirements

• Check daily platelet counts to detect heparin-induced thrombocytopenia. 2, 3
• Measure aPTT at 3,6,12, and 24 hours after initiation, then 4-6 hours after any dose adjustment. 2, 3
• Adjust the infusion rate to maintain aPTT at 1.5-2.0 times control (50-70 seconds). 2, 4
• The duration of UFH infusion should not exceed 48 hours unless ongoing indications exist, such as high embolic risk or recurrent ischemia. 2, 3

Special Populations and Contraindications

• Exclude patients already receiving anticoagulation with enoxaparin, bivalirudin, or fondaparinux from standard UFH dosing protocols. 2
• For patients with heparin-induced thrombocytopenia, use bivalirudin as an alternative (0.25 mg/kg bolus followed by 0.5 mg/kg/hour for 12 hours, then 0.25 mg/kg/hour for 36 hours). 3
• Avoid switching between UFH and LMWH during the same hospitalization, as this increases bleeding risk. 3

Common Pitfalls to Avoid

• Do not use fixed doses of 5,000 U bolus and 1,000 U/hour infusion without weight adjustment, as this approach leads to excess dosing in patients weighing <70 kg and inadequate dosing in heavier patients. 5
• Do not fail to cap the bolus dose at 4,000 U or infusion at 1,000 U/hour, even in patients weighing >70 kg. 2, 5
• Do not discontinue heparin prematurely in high-risk patients before 48 hours without clear clinical justification. 3
• Do not administer UFH concurrently with fibrinolytic agents without strict adherence to lower dosing recommendations, as this combination significantly increases bleeding risk. 1