What is the appropriate conversion of a 2 mg intravenous hydromorphone dose to an equivalent intravenous morphine dose, including the standard potency ratio and a typical 30 % cross‑tolerance reduction for a patient already receiving opioids, and how should the dose be adjusted for opioid‑naïve, elderly, or renal/hepatic impaired patients?

Hydromorphone to Morphine Conversion

For a 2 mg IV hydromorphone dose, the equivalent IV morphine dose is 10 mg using the standard 5:1 conversion ratio; however, for opioid-tolerant patients, reduce this calculated dose by 25-50% (to 5-7.5 mg IV morphine) to account for incomplete cross-tolerance. 1, 2, 3

Standard Conversion Ratio

• The National Comprehensive Cancer Network recommends a 5:1 ratio for IV morphine to IV hydromorphone conversion, meaning 10 mg IV morphine equals 2 mg IV hydromorphone. 1, 2, 3
• The CDC guidelines assign hydromorphone a conversion factor of 4-5 when calculating morphine milligram equivalents (MME), supporting this 5:1 clinical ratio. 3
• Hydromorphone is approximately 5-7 times more potent than morphine on a milligram basis. 1, 2

Cross-Tolerance Adjustment (Critical Step)

When converting between opioids in patients already receiving opioid therapy, you must reduce the calculated equianalgesic dose by 25-50% to account for incomplete cross-tolerance. 1, 2, 3

Application to Your 2 mg IV Hydromorphone Dose:

• Raw calculation: 2 mg IV hydromorphone × 5 = 10 mg IV morphine 1, 3
• Adjusted for cross-tolerance: 10 mg × 0.5 to 0.75 = 5-7.5 mg IV morphine 1, 2, 3
• Start with 5 mg IV morphine (the lower end) for maximum safety, then titrate upward based on pain control. 1, 3

When to Use Full Dose vs. Reduced Dose:

• If pain was well-controlled on hydromorphone: reduce by 25-50% (use 5-7.5 mg morphine). 1, 3
• If pain was poorly controlled: use 100% of calculated dose (10 mg morphine) or increase by up to 25% (12.5 mg). 3
• The reduction is mandatory because different opioids exhibit incomplete cross-tolerance, making patients more sensitive to the new agent. 3

Special Population Adjustments

Opioid-Naïve Patients:

• For opioid-naïve patients, do not use the 2 mg hydromorphone dose as a starting point—this is too high. 2
• Start with 0.015 mg/kg IV hydromorphone (approximately 1-1.5 mg for average adults) or 5-10 mg IV morphine. 1, 2
• The CDC recommends staying within 20-30 MME/day total for opioid-naïve patients with acute pain. 2

Elderly Patients (>70 years):

• Reduce the calculated morphine dose by an additional 50% beyond the cross-tolerance reduction. 1, 2
• For 2 mg IV hydromorphone in elderly: 10 mg × 0.5 (cross-tolerance) × 0.5 (elderly) = 2.5 mg IV morphine as starting dose. 1, 2

Renal Impairment:

• Avoid morphine entirely in patients with CrCl <30 mL/min due to accumulation of toxic metabolites (morphine-3-glucuronide and morphine-6-glucuronide). 1, 3
• Hydromorphone is safer than morphine in renal failure, but if converting to morphine is necessary, start with one-fourth to one-half the usual dose. 1, 2
• Consider alternative opioids (fentanyl, buprenorphine) rather than morphine in severe renal impairment. 2

Hepatic Impairment:

• Start with one-fourth to one-half the calculated morphine dose, as exposure increases 4-fold in moderate hepatic impairment. 1, 2
• For 2 mg IV hydromorphone with hepatic impairment: 10 mg × 0.5 (cross-tolerance) × 0.25-0.5 (hepatic) = 1.25-2.5 mg IV morphine. 1
• Reduce the dose rather than extending dosing intervals to maintain consistent analgesia. 1

Practical Dosing Algorithm

Step 1: Calculate Raw Equianalgesic Dose

• 2 mg IV hydromorphone × 5 = 10 mg IV morphine 1, 3

Step 2: Apply Cross-Tolerance Reduction

• If pain well-controlled: 10 mg × 0.5-0.75 = 5-7.5 mg 1, 3
• If pain poorly controlled: use 10 mg or up to 12.5 mg 3

Step 3: Apply Population-Specific Adjustments

• Elderly: reduce by additional 50% 1, 2
• Renal impairment: avoid morphine if CrCl <30; otherwise reduce by 50-75% 1, 3
• Hepatic impairment: reduce by 50-75% 1

Step 4: Administer and Monitor

• Reassess at 15 minutes (peak effect for IV morphine). 2
• Morphine has a longer onset of action than hydromorphone, increasing risk of dose stacking—wait full 15 minutes before redosing. 2
• If inadequate pain control after 2-3 doses, increase by 50-100%. 2

Breakthrough Dosing After Conversion

• Prescribe breakthrough doses equal to 10-20% of the total 24-hour morphine dose, available every 4 hours as needed. 1, 2, 3
• If patient requires >3-4 breakthrough doses per day, increase the scheduled baseline dose by 25-50%. 1, 2, 3

Common Pitfalls to Avoid

• Do not forget the cross-tolerance reduction—using the raw 5:1 ratio without reduction risks overdosing. 1, 3
• Do not use morphine in severe renal impairment (CrCl <30 mL/min)—toxic metabolites accumulate. 1, 3
• Do not redose morphine before 15 minutes—its longer onset compared to hydromorphone increases dose-stacking risk. 2
• Do not use mixed agonist-antagonist opioids (nalbuphine, butorphanol) in combination with morphine, as this could precipitate withdrawal. 1
• Always institute prophylactic bowel regimen with stimulant laxatives, as constipation is universal with opioid therapy. 1, 2

Monitoring Requirements

• Reassess within 24 hours after conversion, as steady state is reached within this timeframe. 1, 2
• Monitor for respiratory depression, especially during initiation and after dose increases. 2
• Assess pain intensity, sedation level, and adverse effects at each reassessment. 2
• Have naloxone readily available; dilute in normal saline and administer every 30-60 seconds until improvement if respiratory depression occurs. 2