What is the initial infusion rate of Nitroglycerin (NTG) in drops per minute?

Nitroglycerin Infusion Rate in Drops Per Minute

When using non-absorbing tubing with a standard micro-drip set (60 microdrops/mL), start intravenous nitroglycerin at 5-10 mcg/min, which equals 3-6 drops per minute when using a 100 mcg/mL concentration. 1

Initial Setup and Concentration

• Dilute 50 mg nitroglycerin in 500 mL of D5W or normal saline to achieve a standard concentration of 100 mcg/mL 1
• Use an infusion set with a drip chamber that delivers approximately 60 microdrops/mL 1
• Critical: Use non-absorbing tubing, as PVC tubing absorbs significant amounts of nitroglycerin and requires higher doses 2, 1

Starting Dose Calculation

For a 100 mcg/mL concentration with 60 microdrops/mL:

• 5 mcg/min = 3 drops/min (0.05 mL/min × 60 drops/mL)
• 10 mcg/min = 6 drops/min (0.10 mL/min × 60 drops/mL)

The ACC/AHA guidelines recommend starting at 10 mcg/min when using non-absorbing tubing 2, while the FDA label specifies 5 mcg/min as the initial dose with non-absorbing sets and infusion pumps 1

Titration Protocol

• Increase by 5-10 mcg/min (3-6 drops/min) every 3-5 minutes until symptom relief or blood pressure response occurs 2, 3, 1
• If no response at 20 mcg/min (12 drops/min), use larger increments of 10 mcg/min (6 drops/min), then 20 mcg/min (12 drops/min) 2, 3
• Once partial response is achieved, reduce increment size and lengthen intervals between increases 2, 1
• Stop titrating if symptoms resolve—no need to continue increasing for blood pressure effect alone 2, 3

Critical Safety Warnings

Gravity-driven micro-drip infusion is inherently unreliable for precise drug delivery:

• When the roller clamp is fully open ("wide-open" flow), drug delivery becomes unpredictable and can vary up to 3-fold depending on catheter size, IV height, and carrier flow rates 4
• An infusion pump is strongly preferred over gravity drip for nitroglycerin to ensure exact and constant delivery 1, 4

Absolute contraindications:

• Systolic BP <90 mmHg or >30 mmHg below baseline 2, 3, 5
• Sildenafil use within 24 hours or tadalafil within 48 hours (risk of fatal hypotension) 2, 3, 5
• Right ventricular infarction (these patients are preload-dependent) 3, 5
• Marked bradycardia or tachycardia 3, 5

Blood Pressure Targets

• Do not reduce systolic BP below 110 mmHg in normotensive patients 2, 5
• In hypertensive patients, reduce mean arterial pressure by no more than 25% in the first hour 2, 5

Maximum Dosing

• The commonly recommended ceiling is 200 mcg/min (120 drops/min), though this is not an absolute limit 2, 3, 5
• Doses up to 400 mcg/min have been safely used in refractory cases 3, 5

Practical Recommendation

Given the significant variability and imprecision of gravity-driven micro-drip delivery, use a volumetric infusion pump instead of counting drops. 1, 4 If a pump is unavailable and you must use gravity drip, start at 6 drops/min (10 mcg/min with 100 mcg/mL concentration) and titrate by 3-6 drops/min every 3-5 minutes, but recognize this method carries substantial risk of dosing errors. 1, 4