What is the standard dosage for fentanyl (opioid analgesic)?

Fentanyl Dosing Guidelines

Route-Specific Dosing

Intravenous/Intramuscular Administration

For acute analgesia, fentanyl 100 mcg (0.1 mg) IV is approximately equivalent to 10 mg morphine or 75 mg meperidine, with onset of action almost immediate IV and 7-8 minutes IM. 1

• IV administration: Maximal analgesic effect occurs within several minutes, with usual duration of 30-60 minutes after a single dose up to 100 mcg 1
• IM administration: Duration of action extends to 1-2 hours 1
• Peak respiratory depression: Occurs 5-15 minutes post-injection and may outlast the analgesic effect 1

Transdermal Fentanyl Patch Dosing

Transdermal fentanyl should only be initiated in opioid-tolerant patients with stable, well-controlled pain on short-acting opioids, starting with the lowest appropriate patch strength based on 24-hour opioid requirements. 2

Conversion Table from Other Opioids to Transdermal Fentanyl:

Fentanyl Patch	Oral Morphine	IV/SubQ Morphine	Oral Oxycodone	Oral Tramadol
25 mcg/h	60 mg/day	20 mg/day	30 mg/day	200 mg/day
50 mcg/h	120 mg/day	40 mg/day	60 mg/day	400 mg/day
75 mcg/h	180 mg/day	60 mg/day	90 mg/day	600 mg/day
100 mcg/h	240 mg/day	80 mg/day	120 mg/day	800 mg/day

2, 3

Critical Dosing Algorithm:

1. Calculate total 24-hour opioid requirement of current medication 2
2. Convert to oral morphine equivalent if not already using morphine, oxycodone, hydromorphone, or tramadol 2
3. Select appropriate patch strength from conversion table 2
4. Reduce initial dose by 25-50% if pain was well-controlled, to account for incomplete cross-tolerance 3, 4
5. Use 100% of calculated dose (or increase by 25%) only if previous pain control was inadequate 2

Essential Clinical Considerations:

• Patch duration: Typically 72 hours, but some patients require 48-hour replacement 2
• Breakthrough medication: Prescribe short-acting opioid for first 8-24 hours until steady state achieved (2-3 days) 2, 3
• Dose titration: Adjust patch strength after 2-3 days based on average daily breakthrough medication requirements 2, 3
• Contraindications: Unstable pain requiring frequent dose changes, fever, application of external heat sources (accelerates absorption), non-opioid-tolerant patients 2, 1

Continuous Infusion Dosing

When converting from continuous IV fentanyl infusion to transdermal patch, use a 1:1 ratio (mcg/hour IV = mcg/hour transdermal), though additional titration may be necessary. 2

• Continuous subcutaneous fentanyl infusions typically start at 100-1000 mcg/24 hours for cancer pain 5
• The clinically derived fentanyl to morphine potency ratio for continuous infusion is approximately 68:1 (range 15-100), with recommended conversion of 150-200 mcg fentanyl per 10 mg morphine 5
• High-dose continuous IV fentanyl infusions up to 4250 mcg/hour have been safely used in refractory cancer pain 6

Critical Safety Warnings

Monitor closely for respiratory depression during the first 24-72 hours, as diminished CO2 sensitivity may persist up to 4 hours after a single 600 mcg dose and respiratory depression duration often exceeds analgesic duration. 1

• Fentanyl accumulates in skeletal muscle and fat, releasing slowly into blood 1
• Volume of distribution is 4 L/kg 1
• Plasma protein binding decreases with increasing drug ionization; pH alterations affect CNS distribution 1
• Common adverse effects include respiratory depression, nausea, vomiting, CNS effects, orthostatic hypotension, constipation, and miosis 1

Special Populations

• Opioid-naive patients: Transdermal fentanyl is contraindicated; use only in opioid-tolerant patients 2, 3
• Starting dose for first-line therapy: In select populations, 1.25 mg transdermal patch (50% of 2.5 mg patch) has been used safely as first-line strong opioid 7