What is the recommended dosage for intravenous (IV) Nitroglycerin (NTG)?

Recommended Dosage for Intravenous (IV) Nitroglycerin

Intravenous nitroglycerin should be initiated at 5 mcg/min through non-absorbing tubing and titrated up by 5 mcg/min every 3-5 minutes until symptom relief or blood pressure response is observed. 1, 2

Initial Preparation and Administration

• IV nitroglycerin must be diluted prior to infusion:

  • Standard dilution: 50 mg in 500 mL D5W or NS (100 mcg/mL)
  • Alternative dilution: 5 mg in 100 mL (50 mcg/mL)
  • Maximum concentration should not exceed 400 mcg/mL 1

• Use non-absorbing tubing (critical for accurate dosing)

  • PVC tubing absorbs nitroglycerin, requiring higher doses
  • Non-absorbing tubing requires lower doses 1

Dosing Algorithm

1. Starting dose: 5 mcg/min when using non-absorbing tubing 2, 1
2. Initial titration:
   • Increase by 5 mcg/min every 3-5 minutes until response is noted
   • If no response at 20 mcg/min, increase by 10 mcg/min increments
   • If still no response, increase by 20 mcg/min increments 2, 1
3. After partial response:
   • Reduce increment size
   • Lengthen interval between increases 1
4. Maintenance: Continue at effective dose; may require periodic increases if used beyond 24 hours due to tolerance 2

Maximum Dosage

• Common ceiling: 200 mcg/min 2
• Higher doses (300-400 mcg/min) have been used for prolonged therapy without increasing methemoglobin levels 2
• Ultra-high doses (up to several mg) have been reported in severe cases of Sympathetic Crashing Acute Pulmonary Edema (SCAPE) 3

Monitoring Parameters

• Blood pressure and heart rate
• Clinical symptoms
• Watch for hypotension (SBP <90 mmHg or 30 mmHg below baseline)
• Monitor for reflex tachycardia which can worsen myocardial ischemia 4

Important Contraindications and Precautions

• Absolute contraindication: Use of phosphodiesterase-5 inhibitors
  • Sildenafil within previous 24 hours
  • Tadalafil within previous 48 hours
  • Vardenafil (timing not established, but at least 24 hours) 2, 4
• Relative contraindications:
  • Systolic BP <90 mmHg
  • Right ventricular infarction
  • Severe aortic stenosis 4

Special Considerations

• Hypersensitivity: Some patients (especially those with normal/low LV filling pressures) may respond fully to doses as low as 5 mcg/min 1
• Tolerance: Develops after 24 hours of continuous therapy; may require dose increases to maintain efficacy 2
• For prolonged therapy: Consider nitrate-free intervals of 10-14 hours to prevent tolerance 4

Clinical Pearls

• Flush or replace the infusion set when changing concentration to avoid delayed dose delivery 1
• For patients with refractory chest pain despite sublingual NTG, IV NTG is recommended in the absence of contraindications 2
• If chest pain persists despite IV NTG, consider adding morphine sulfate (1-5 mg IV) with careful blood pressure monitoring 2