What are the equianalgesic dose equivalents for common opioids in an average adult with normal renal and hepatic function and no opioid tolerance, and how should the dose be reduced when switching, especially in elderly patients or those with renal or hepatic impairment?

Opioid Equianalgesic Dosing

For opioid-naïve adults with normal organ function, use standard conversion ratios (oral morphine 30 mg = oral hydromorphone 6 mg = IV morphine 10 mg = IV hydromorphone 1.5 mg), but when switching between opioids, reduce the calculated equianalgesic dose by 25-50% to account for incomplete cross-tolerance; in elderly patients or those with renal/hepatic impairment, start with 25-50% of the calculated dose. 1

Standard Equianalgesic Conversion Ratios

Oral Opioid Equivalents (relative to oral morphine 30 mg)

• Morphine oral: 30 mg 1
• Hydromorphone oral: 6 mg (5:1 ratio to morphine; some sources cite 4:1 or 7.5:1, but 5:1 is most commonly used) 1, 2, 3
• Oxycodone oral: Approximately 20 mg 1
• Hydrocodone oral: Approximately 30 mg 1
• Codeine oral: 200 mg 1, 2
• Oxymorphone oral: 10 mg 2

Parenteral Opioid Equivalents

• Morphine IV: 10 mg (oral-to-IV ratio is 3:1) 1, 2
• Hydromorphone IV: 1.5 mg (oral hydromorphone-to-IV hydromorphone is approximately 5:1; IV morphine-to-IV hydromorphone is 5-7:1) 1, 4, 2
• Fentanyl IV: 0.1 mg (100 mcg) - note this applies only to IV fentanyl compared with other IV opioids, NOT transdermal 1

Special Considerations for Methadone

• Methadone conversion is dose-dependent and non-linear: The higher the baseline morphine dose, the more potent methadone becomes relative to morphine 1
• For oral morphine 100-300 mg/day, use a conversion ratio of approximately 8:1 (morphine:methadone) 1
• For oral morphine >300 mg/day, ratios may reach 12:1 or higher 1
• Critical warning: These ratios should NEVER be used in reverse when converting FROM methadone TO other opioids 1, 5

Methadone-to-Other Opioid Conversions

• When discontinuing methadone and switching to another opioid, use a conservative 1:1 ratio (oral methadone:oral morphine) on day 1, supplemented with short-acting opioids as needed 1
• Methadone's long half-life (24-36 hours) means it takes several days to clear; expect to increase the replacement opioid dose daily as residual methadone clears 1, 5
• Research data suggest the actual ratio for oral methadone to oral morphine equivalent is approximately 1:4.7, and for IV methadone to morphine equivalent is 1:13.5, but clinical application requires the conservative day-1 approach 5

Critical Dose Reduction Rules When Switching Opioids

The 25-50% Reduction Rule

• When pain was well-controlled: Calculate the equianalgesic dose of the new opioid, then reduce by 25-50% to account for incomplete cross-tolerance 1, 4, 2
• When pain was poorly controlled: May use 100% of the calculated equianalgesic dose or even increase by 25% 1
• This reduction is mandatory because different opioids have incomplete cross-tolerance at the receptor level, meaning patients are more sensitive to a new opioid than predicted by simple conversion ratios 1, 6

Example Calculation: IV Morphine to IV Hydromorphone

1. Patient receiving IV morphine 8 mg/hour = 192 mg/day 1
2. Using 5:1 ratio: 192 mg morphine ÷ 5 = 38.4 mg hydromorphone/day 1
3. If pain was well-controlled, reduce by 25-50%: 38.4 mg × 0.5 = 19.2 mg/day = 0.8 mg/hour 1
4. If pain was poorly controlled, may use full 38.4 mg/day (1.6 mg/hour) or increase to 48 mg/day (2 mg/hour) 1

Special Population Dosing Adjustments

Elderly Patients (>70 years)

• Start at the lower end of recommended dose ranges (e.g., 2 mg oral hydromorphone rather than 4 mg for opioid-naïve patients) 4
• Reduce calculated conversion doses by 50% rather than 25% when switching opioids 4
• Reassess more frequently (every 4-6 hours initially) for excessive sedation or respiratory depression 7

Renal Impairment

• Avoid morphine and codeine entirely when creatinine clearance <30 mL/min due to accumulation of toxic metabolites (morphine-3-glucuronide, morphine-6-glucuronide, norcodeine) 1, 7, 2
• Hydromorphone: Reduce dose by 25-50% in moderate-to-severe renal impairment; monitor for myoclonus, hyperalgesia, and seizures from 3-glucuronide metabolite accumulation 4, 7, 2
• Fentanyl is safest in CKD stages 4-5 (eGFR <30 mL/min) because it lacks renally cleared toxic metabolites 7, 2
• Oxycodone, hydrocodone, oxymorphone: Use with caution; reduce doses by 25-50% 2

Hepatic Impairment

• Reduce starting doses by 25-50% for all opioids due to decreased first-pass metabolism and glucuronidation 4, 2
• Hydromorphone exposure increases 4-fold in moderate hepatic impairment 4
• Use shorter dosing intervals rather than extending intervals to maintain steady analgesia 4
• Avoid methadone due to extensive hepatic metabolism and risk of accumulation 1

Breakthrough Pain Dosing

Standard Breakthrough Dose Calculation

• Prescribe 10-20% of the total 24-hour opioid dose as the breakthrough dose, available every 1-4 hours as needed 1, 4, 2
• Use the same opioid for breakthrough as for scheduled dosing when possible 1
• Example: Patient on 60 mg oral morphine/day should receive 6-12 mg oral morphine for breakthrough 4

When to Increase Scheduled Dose

• If patient requires >3-4 breakthrough doses per day, increase the scheduled baseline dose by 25-50% 1, 4, 2
• Calculate total opioid used in 24 hours (scheduled + all breakthrough doses), then redistribute as new scheduled regimen 1

Transmucosal Fentanyl Exception

• Transmucosal fentanyl (lozenge, buccal tablet, sublingual film) is ONLY for opioid-tolerant patients (≥60 mg oral morphine equivalents daily for ≥1 week) 1, 7
• No reliable equianalgesic dose exists for transmucosal fentanyl; always start with lowest dose (100-200 mcg) and titrate 1
• Reserved for brief episodes of breakthrough pain, not for inadequate around-the-clock dosing 1

Transdermal Fentanyl Conversions

Critical Safety Warnings

• Never use fentanyl patches in opioid-naïve patients - this is an absolute contraindication 7
• Avoid heat sources (heating pads, hot tubs, electric blankets) as they accelerate absorption and can cause fatal overdose 7
• Patches are only for stable pain; do not use for rapidly escalating or unstable pain requiring frequent adjustments 7

Conversion to Transdermal Fentanyl

• Use manufacturer-specific conversion tables; do NOT use standard IV fentanyl ratios 1, 2
• Fentanyl patches reach therapeutic levels in 8-24 hours and steady state in 2-3 days 7
• Provide adequate short-acting opioid coverage during the first 12-24 hours after patch application 7
• Reassess patch site every 48-72 hours 7

Common Pitfalls and How to Avoid Them

Pitfall 1: Using the Same Ratios for Methadone in Both Directions

• Never apply morphine-to-methadone ratios when converting FROM methadone 1, 5
• Methadone's long half-life creates a moving target; use 1:1 on day 1 and titrate daily 1

Pitfall 2: Forgetting the 25-50% Dose Reduction

• Always reduce calculated doses when switching opioids unless pain was uncontrolled 1, 4, 2
• Incomplete cross-tolerance means patients are more sensitive to new opioids than conversion tables suggest 1, 6

Pitfall 3: Using Morphine in Renal Failure

• Morphine and codeine accumulate toxic metabolites in renal impairment - avoid entirely when CrCl <30 mL/min 1, 7
• Switch to fentanyl or use hydromorphone at reduced doses with close monitoring 7, 2

Pitfall 4: Inadequate Monitoring After Conversion

• Reassess pain and sedation every 4-6 hours for the first 24-48 hours after any opioid switch 4, 7
• Monitor respiratory rate (goal >8-10 breaths/min), sedation level, and for signs of toxicity (myoclonus, confusion, pinpoint pupils) 4, 7

Pitfall 5: Confusing IV and Transdermal Fentanyl Conversions

• IV fentanyl conversion ratios do NOT apply to transdermal patches 1, 7
• Always use manufacturer tables for patch conversions 1, 2

Pitfall 6: Ignoring Variation in Published Tables

• Equianalgesic tables vary significantly across institutions and sources, particularly for tramadol and hydromorphone 3, 8
• Use the ratios from established guidelines (NCCN, CDC) rather than pharmaceutical company materials 1, 2, 8
• Recognize that all conversion ratios are approximations requiring clinical judgment 2, 3, 8

Practical Conversion Algorithm

Step 1: Calculate Total 24-Hour Current Opioid Dose

• Include all scheduled doses PLUS average daily breakthrough medication use 1, 2

Step 2: Convert to Morphine Milligram Equivalents (MME)

• Multiply current opioid dose by its conversion factor 2
• Example: Hydromorphone 12 mg/day × 4 (CDC conversion factor) = 48 MME/day 2

Step 3: Convert to New Opioid Using Equianalgesic Ratios

• Divide MME by the new opioid's conversion factor 2
• Example: 48 MME ÷ 4 = 12 mg hydromorphone/day 2

Step 4: Apply Dose Reduction for Incomplete Cross-Tolerance

• If pain well-controlled: reduce by 25-50% 1, 2
• If pain poorly controlled: use 100% or increase by 25% 1
• If elderly or organ impairment: reduce by 50% 4, 7, 2

Step 5: Divide into Appropriate Dosing Schedule

• Immediate-release: divide by 6 (every 4 hours) 1
• Extended-release: divide by 2 (every 12 hours) or by 1 (every 24 hours) depending on formulation 1

Step 6: Prescribe Breakthrough Medication

• Calculate 10-20% of total daily dose 1, 4, 2
• Make available every 1-4 hours as needed 1, 4

Step 7: Monitor and Titrate

• Reassess at peak effect: 60 minutes for oral, 15 minutes for IV 4
• If >3-4 breakthrough doses needed daily, increase scheduled dose by 25-50% 1, 4, 2