What concentration should be used for a remifentanil infusion (drip)?

Remifentanil Infusion Concentration

Remifentanil must be diluted before administration and the standard concentration used is 20-50 mcg/mL, with 50 mcg/mL being the most commonly recommended concentration for continuous infusion. 11

Standard Preparation

The FDA-approved labeling explicitly states that remifentanil should not be administered without dilution 11. The typical preparation involves:

• Recommended concentration: 50 mcg/mL (1 mg remifentanil in 20 mL of compatible diluent)
• Alternative concentration: 20-25 mcg/mL for lower infusion rates or pediatric use
• Compatible diluents include: normal saline, 5% dextrose in water, 5% dextrose in normal saline, or lactated Ringer's solution

Clinical Context for Dosing

The concentration choice matters because it affects the precision of dose titration:

For general anesthesia maintenance:

• Adults typically require 0.05-2 mcg/kg/min 11
• Using 50 mcg/mL concentration allows for easier titration at these rates
• The infusion must be administered via an infusion pump, with the injection site close to the venous cannula 11

For postoperative analgesia:

• Lower rates of 0.025-0.2 mcg/kg/min are used 11
• A more dilute concentration (20-25 mcg/mL) may provide better precision at these lower rates

For pediatric patients:

• Maintenance rates of 0.05-1.3 mcg/kg/min 11
• Consider 25 mcg/mL concentration for better dose accuracy in smaller patients

Critical Safety Points

• All IV tubing must be cleared at the time of discontinuation to prevent inadvertent bolus administration 11
• The ultra-short context-sensitive half-time (3-5 minutes) means patients recover rapidly once the infusion stops 2
• During cardiopulmonary bypass, volume of distribution increases 2.41-fold, requiring dose adjustments 3
• In hypothermic conditions during cardiac surgery, consider reducing the dose by 30% at 32°C and 60% below 28°C 4

Practical Preparation

For a 1 mg vial:

• Add to 20 mL diluent = 50 mcg/mL (standard)
• Add to 40 mL diluent = 25 mcg/mL (for lower rates)
• Add to 50 mL diluent = 20 mcg/mL (for very low rates or pediatrics)

The 50 mcg/mL concentration provides the best balance between volume administration and dosing precision for most adult applications, while allowing for the wide range of infusion rates required across different phases of anesthesia.