GTN Infusion Flow Rate in 100 mL Normal Saline
Start the GTN infusion at 10 mcg/min (equivalent to 6 mL/hour for a standard 50 mg GTN in 100 mL NS concentration) and titrate upward by 10 mcg/min every 3-5 minutes until symptoms resolve or blood pressure responds. 1, 2
Standard Concentration and Initial Rate
- The standard preparation is 50 mg GTN in 100 mL normal saline, yielding a concentration of 500 mcg/mL 1, 2
- Begin at 10 mcg/min, which equals 6 mL/hour on an infusion pump 1, 2
- For non-absorbing tubing systems, starting at 5-10 mcg/min is acceptable 2
Titration Protocol
- Increase by 10 mcg/min (6 mL/hour) every 3-5 minutes for the first 20 minutes until symptom relief or blood pressure response occurs 1, 2
- If no response at 20 mcg/min, use larger increments of 10-20 mcg/min 1, 2
- Once partial response is achieved, reduce the increment size and lengthen the interval between increases 2
- Stop titrating once symptoms resolve—do not continue increasing solely for blood pressure effect 2
Maximum Dose Considerations
- The commonly recommended ceiling is 200 mcg/min (120 mL/hour), though this is not an absolute limit 1, 2
- Doses up to 300-400 mcg/min have been safely administered for 2-4 weeks without increasing methemoglobin levels 1, 2
Critical Safety Parameters Before Starting
Do not initiate GTN if:
- Systolic BP <90 mmHg or >30 mmHg below baseline 1, 2
- Phosphodiesterase-5 inhibitor use within 24 hours (sildenafil) or 48 hours (tadalafil) - this is an absolute contraindication due to risk of profound hypotension, MI, and death 1, 2
- Marked bradycardia or tachycardia is present 2
During infusion:
- Target systolic BP should not fall below 110 mmHg in normotensive patients 1, 2
- In acute heart failure, GTN is recommended for patients with systolic BP >110 mmHg and may be used cautiously between 90-110 mmHg with frequent monitoring 1
- In hypertensive patients, do not reduce mean arterial pressure by more than 25% 2
Important Practical Consideration
If using a large-bore cannula (e.g., grey cannula), start with a faster initial infusion rate to ensure drug delivery begins promptly—at 1 mL/hour, it takes over 6 minutes for GTN to enter the body through a large cannula versus 1.5 minutes through a smaller pink cannula 3. This is particularly critical in acute left ventricular failure.
Tolerance Management
- Tolerance develops after 24 hours of continuous infusion and is dose and duration dependent 1, 2
- Transition to oral/topical nitrates within 24 hours once the patient is stable and symptom-free for 12-24 hours to prevent rebound vasoconstriction 1, 2
- Consider incremental dosing increases if therapy extends beyond 24 hours 2