What are the recommended fentanyl IV bolus and continuous infusion (perfusion) doses for opioid‑naïve adults, opioid‑tolerant adults, and pediatric patients?

Fentanyl Bolus and Continuous Infusion Dosing

Opioid-Naïve Adults

For opioid-naïve adults, administer an initial IV fentanyl bolus of 50–100 µg (approximately 1–2 µg/kg) slowly over several minutes, with supplemental 25 µg doses every 2–5 minutes until pain control is achieved. 1

Initial Bolus Administration

• The onset of analgesia occurs within 1–2 minutes, with effects lasting 30–60 minutes 1
• Critical safety rule: Always administer IV fentanyl slowly over several minutes—rapid injection can produce glottic and chest wall rigidity even at doses as low as 1 µg/kg 1
• Allow 2–3 minutes between doses for full effect before administering additional medication 1

Continuous Infusion Initiation

• After achieving initial pain control with boluses, start a continuous infusion individualized based on response 1
• Bolus doses should be available every 5 minutes as needed during infusion 1
• Dose escalation rule: If the patient requires two bolus doses within one hour, double the infusion rate 1

Elderly Patients

• Reduce the initial fentanyl dose by ≥50% regardless of route of administration 1

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Opioid-Tolerant Adults

For opioid-tolerant patients, calculate the 24-hour opioid requirement, convert to morphine equivalents, then initiate fentanyl at an appropriate rate with a 25–50% dose reduction to account for incomplete cross-tolerance. 1

Defining Opioid Tolerance

Patients are considered opioid-tolerant if taking any of the following for ≥1 week: 1

• ≥60 mg oral morphine daily
• ≥30 mg oral oxycodone daily
• ≥8 mg oral hydromorphone daily
• ≥25 mg oral oxymorphone daily
• Equianalgesic doses of another opioid

Conversion from Continuous IV Morphine to IV Fentanyl

Use a fentanyl:morphine potency ratio of 60:1: 2, 1

1. Calculate the 24-hour morphine dose
2. Multiply by 1/60 to get the fentanyl dose
3. Divide by 4 to correct for morphine's longer half-life
4. Reduce the calculated dose by 25–50% for incomplete cross-tolerance 1

Conversion from IV Fentanyl to Transdermal Fentanyl

• Use a 1:1 ratio (mcg IV/hour = mcg/hr transdermal) 1
• Provide short-acting opioid rescue medication equal to 10–20% of the total 24-hour dose during the first 8–24 hours after patch application 1

Breakthrough Dosing

• Calculate rescue doses as 10–20% of the total 24-hour opioid dose 1
• After 2–3 days at steady state, adjust the basal fentanyl dose based on average daily rescue medication requirements 1
• If more than 3–4 breakthrough doses are required per day, increase the scheduled baseline dose by 25–50% 3, 1

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Pediatric Patients

For pediatric patients, administer an initial bolus of 1–2 µg/kg IV slowly over several minutes, with higher doses of 1–5 µg/kg often used for intubation/RSI. 1

Standard Concentration

• Use a standard concentration of 50 µg/mL for pediatric fentanyl infusions, which allows for precise dosing and minimizes volume administration 1

Conversion from Continuous IV Fentanyl to Enteral Methadone (Neonates)

For neonates on continuous IV fentanyl for 7–14 days: 2

1. Calculate the 24-hour fentanyl dose using the current hourly infusion rate
2. Multiply the daily fentanyl dose by 100 to calculate the equipotent amount of methadone (fentanyl:methadone ratio = 100:1)
3. Divide this amount by 6 (correction for methadone's longer half-life) to calculate initial total daily methadone dose
4. Provide this amount orally in 4 divided doses every 6 hours on day 1
5. Day 2: Provide 80% of original daily dose in 3 divided doses every 8 hours
6. Day 3: Provide 60% of original daily dose in 3 divided doses every 8 hours
7. Day 4: Provide 40% of original daily dose in 2 divided doses every 12 hours
8. Day 5: Provide 20% of original daily dose × 1
9. Day 6: Discontinue methadone

For neonates on continuous IV fentanyl >14 days: 2

• Follow the same calculation steps 1–2 above
• Days 1–2: Divide by 6 and provide in 4 divided doses every 6 hours for 48 hours
• Days 3–4: Provide 80% of original daily dose in 3 divided doses every 8 hours for 48 hours
• Days 5–6: Provide 60% of original daily dose in 3 divided doses every 8 hours for 48 hours
• Days 7–8: Provide 40% of original daily dose in 2 divided doses every 12 hours for 48 hours
• Days 9–10: Provide 20% of original daily dose once per day for 48 hours
• Day 11: Discontinue methadone

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Critical Safety Monitoring (All Populations)

Respiratory Depression Management

• Monitor patients for at least 24 hours after dose initiation or increase due to fentanyl's mean elimination half-life of approximately 17 hours 1
• Keep naloxone (0.2–0.4 mg IV for adults; 0.1 mg/kg for pediatrics) and resuscitation equipment immediately available 2, 1
• Respiratory depression may persist longer than the analgesic effect; repeated or continuous naloxone dosing may be required due to naloxone's short half-life (30–45 minutes) 1
• Monitor oxygen saturation continuously 2

Drug Interaction Risks

• Co-administration of fentanyl with benzodiazepines or other sedatives markedly increases the risk of apnea—the interaction is synergistic for respiratory depression 1
• Exercise extreme caution with co-administration and provide enhanced monitoring 1

Special Population Considerations

• Renal impairment: Fentanyl is preferred over morphine because it does not generate renally cleared toxic metabolites and can be used without dose adjustment in renal failure 1
• Avoid morphine, hydromorphone, and codeine in patients with fluctuating renal function due to accumulation of neurotoxic metabolites 1

Common Pitfalls to Avoid

• Never use rapid IV push—always administer boluses slowly over 2–3 minutes to prevent chest wall rigidity 1
• Do not administer naloxone to a newborn infant whose mother is suspected of long-term opioid use because of the risk of seizures/acute withdrawal 2
• Avoid heat exposure (fever, hot environments) as it can accelerate fentanyl absorption from transdermal patches, potentially causing overdose 1