What is the recommended dosage and administration of intravenous (IV) nitroglycerin for an adult patient with acute coronary syndrome, such as myocardial infarction or severe angina, and a history of cardiovascular disease?

Intravenous Nitroglycerin Dosing and Administration

For adults with acute coronary syndrome, start IV nitroglycerin at 5-10 mcg/min (using non-absorbing tubing) after a 15 mcg bolus, and titrate upward by 5-10 mcg/min every 3-5 minutes while maintaining systolic blood pressure ≥90 mmHg, targeting symptom relief or a 10% reduction in mean arterial pressure for normotensive patients (30% for hypertensive patients). 1, 2, 3

Pre-Administration Requirements

Blood Pressure Threshold:

• Systolic BP must be ≥90 mmHg before initiating IV nitroglycerin 1, 4
• Contraindicated if SBP <90 mmHg or ≥30 mmHg below baseline 4
• A single sublingual nitroglycerin (0.4 mg) may be attempted even with SBP <90 mmHg if there is ongoing ischemic pain and IV access is established, but requires extreme caution 1

Critical Exclusions:

• Assess for right ventricular infarction before administration, especially in inferior MI patients—these patients are critically dependent on adequate RV preload and can experience profound, life-threatening hypotension with nitrates 1, 4, 5
• Obtain right-sided ECG (V3R-V4R) in all inferior STEMI patients before considering nitrates 4
• Contraindicated within 24 hours of sildenafil or 48 hours of tadalafil use due to risk of profound hypotension and death 4

Initial Dosing Protocol

Starting Dose (Non-Absorbing Tubing):

• Administer 15 mcg bolus injection 1, 2
• Begin infusion at 5-10 mcg/min using an infusion pump 1, 3
• Note: FDA labeling specifies 5 mcg/min as the initial dose when using non-absorbing tubing, as older studies used PVC tubing requiring 25 mcg/min or higher 3

Titration Schedule:

• Increase by 5-10 mcg/min every 3-5 minutes during initial titration 1, 2, 3
• If no response at 20 mcg/min, increase increments to 10 mcg/min, then 20 mcg/min 1, 3
• Once partial blood pressure response is observed, reduce dose increments and lengthen intervals between increases 3

Titration Endpoints

Primary Targets:

• Control of clinical symptoms (chest pain, dyspnea, heart failure) 1, 2, 5
• Decrease mean arterial pressure by 10% in normotensive patients 1, 2, 5
• Decrease mean arterial pressure by 30% in hypertensive patients 1, 2, 5
• Never allow systolic blood pressure to fall below 90 mmHg—this is an absolute floor 1, 2, 5

Secondary Hemodynamic Targets:

• Increase in heart rate >10 beats/min (but not usually >110 beats/min) 1
• Decrease in pulmonary artery end-diastolic pressure of 10-30% 1

Maximum Dosing and Tolerance

Upper Dose Limits:

• Although there is no absolute maximum, doses >200 mcg/min are associated with increased risk of hypotension 1, 5
• At doses >200 mcg/min, consider substituting another vasodilator such as a calcium channel blocker 1, 5
• Maximum concentration should not exceed 400 mcg/mL 3

Nitrate Tolerance:

• Tachyphylaxis commonly develops after 24-48 hours of continuous infusion 4
• If tolerance develops, infusion rate can be increased, but effectiveness usually returns after 12 hours off nitroglycerin 1

Special Populations and Considerations

Anterior MI Patients:

• Derive particular mortality benefit from IV nitroglycerin, with demonstrated improved hospital survival (14% vs 26% mortality, p<0.01) in one randomized trial 1, 2
• Should receive sublingual nitroglycerin 0.25-0.5 mg or spray 400 mcg every 5-10 minutes before IV access is established 2

Patients on Beta-Blockers:

• The combination of IV nitroglycerin with beta-blockers (e.g., carvedilol, metoprolol) is well-tolerated and theoretically attractive 1, 2
• Beta-blockers reduce the risk of reflex tachycardia from nitroglycerin, allowing more aggressive titration 2

Inferior MI with Old Infarction:

• Hemodynamic vulnerability is substantially reduced in chronic/old MI unless there is residual RV dysfunction or ongoing ischemia 5
• Still requires careful titration with the same blood pressure thresholds 5

Hypersensitive Patients:

• Some patients with normal or low left ventricular filling pressures may respond fully to doses as small as 5 mcg/min 3
• These patients require especially careful titration and monitoring 3

Monitoring Requirements

Continuous Monitoring:

• Blood pressure and heart rate must be monitored every 3-5 minutes during titration 1, 2, 4
• Invasive hemodynamic monitoring (pulmonary capillary wedge pressure) may be preferable if high doses are required, blood pressure instability ensues, or there is clinical doubt about left ventricular filling pressure adequacy 1

Management of Adverse Effects

Hypotension Protocol:

• Immediately discontinue nitroglycerin 1, 5
• Elevate legs to increase venous return 1, 5
• Administer rapid IV fluid bolus 1, 5
• Give atropine if excessive bradycardia is present 1, 5

Other Adverse Effects:

• Nitroglycerin frequently causes headache 1
• May aggravate hypoxemia by increasing ventilation-perfusion mismatch 1

Preparation and Administration

Dilution:

• Dilute 50 mg nitroglycerin in 500 mL D5W or 0.9% NaCl to yield 100 mcg/mL 3
• Alternatively, dilute 5 mg in 100 mL to yield 50 mcg/mL 3
• Use glass bottles and non-PVC, non-absorbing tubing 3
• Do not mix with other drugs 3
• If concentration is adjusted, flush or replace the infusion set before using the new concentration 3

Clinical Indications Beyond ACS

Established Benefits:

• Congestive heart failure or pulmonary edema complicating acute MI 1
• Ongoing myocardial ischemic pain 1
• Perioperative hypertension 6
• Unstable angina and coronary vasospasm 7, 6