What is the recommended protocol for administering fentanyl (opioid) intravenously (IV)?

How to Administer Intravenous Fentanyl

Administer IV fentanyl slowly over several minutes at an initial bolus dose of 1-2 mcg/kg for opioid-naïve patients, or 25-50 mcg for breakthrough pain in opioid-tolerant patients, with repeat boluses available every 5 minutes as needed. 1, 2

Critical Administration Rule

Never administer fentanyl rapidly—chest wall rigidity and glottic spasm can occur with doses as low as 1 mcg/kg when given too quickly. 1, 2 This is the most important safety consideration and the primary reason for slow administration over several minutes. 1

Initial Bolus Dosing Protocol

For Opioid-Naïve Patients

• Give 1-2 mcg/kg IV fentanyl as the initial bolus, administered slowly over several minutes. 1, 2
• For brain-injured patients requiring intubation, use higher bolus doses of 3-5 mcg/kg, but reduce doses in hemodynamically unstable patients. 1, 2
• Allow 2-3 minutes for fentanyl to take effect before administering additional medications. 1

For Opioid-Tolerant Patients

• Administer 25-50 mcg IV bolus doses every 5 minutes as required for breakthrough pain. 2
• If the patient is already receiving a fentanyl infusion and develops pain, give a bolus dose equal to two times the hourly infusion dose. 2

Starting a Continuous Infusion

• After achieving initial pain control with boluses, initiate the continuous infusion at a rate individualized based on the patient's response to the initial boluses. 2
• If the patient requires two bolus doses within one hour, double the infusion rate. 1, 2

Converting from Other Opioids to IV Fentanyl

Conversion from IV Morphine

• Use a fentanyl:morphine potency ratio of 60:1. 1, 2
• Calculate the 24-hour morphine dose, multiply by 1/60 to get the fentanyl dose, then divide by 4 to correct for morphine's longer half-life. 1, 2
• Reduce the calculated equianalgesic dose by 25-50% to account for incomplete cross-tolerance, especially if pain was previously well-controlled. 1, 2, 3

Example Calculation

If a patient is receiving 192 mg/day IV morphine:

• 192 mg ÷ 60 = 3.2 mg fentanyl per day
• 3.2 mg ÷ 4 (half-life correction) = 0.8 mg fentanyl per day
• Reduce by 50%: 0.4 mg (400 mcg) fentanyl per day = approximately 17 mcg/hour infusion 1, 2

Essential Safety Monitoring

Immediate Preparation Required

• Have naloxone (0.1 mg/kg IV or 0.2-0.4 mg for adults) immediately available. 1, 2
• Be prepared to provide respiratory support at all times. 1, 2
• Have vasoconstrictors (ephedrine or metaraminol) immediately available to treat hypotension. 1

Monitoring Duration and Parameters

• Monitor patients for at least 24 hours after dose initiation or increase due to fentanyl's mean half-life of approximately 17 hours. 1, 2
• Monitor oxygen saturation continuously. 1
• Respiratory depression may last longer than the analgesic effect of fentanyl, requiring extended monitoring. 2

Critical Drug Interaction

There is significantly increased risk of apnea when fentanyl is combined with benzodiazepines or other sedatives—exercise extreme caution with co-administration. 1, 2

Dose Adjustments for Special Populations

• Reduce doses by 50% or more in elderly patients. 2
• Adjust doses based on considerations of size, age, and organ dysfunction. 2
• Fentanyl may be preferred over morphine in patients with renal failure due to accumulation of renally cleared morphine metabolites. 2, 3

Common Pitfalls to Avoid

• Rapid administration: This is the most dangerous error—always administer slowly over several minutes. 1, 2
• Starting with too high a conversion dose: Always reduce by 25-50% for incomplete cross-tolerance when converting from other opioids. 1, 2, 3
• Inadequate monitoring duration: Respiratory depression can occur late, requiring monitoring for at least 24 hours. 1, 2
• Underestimating benzodiazepine interaction: The combination dramatically increases apnea risk. 1, 2