What is the intravenous morphine dose equivalent to 4 mg oral hydromorphone?

Oral Hydromorphone to IV Morphine Conversion

4 mg oral hydromorphone is equivalent to approximately 12-15 mg IV morphine.

Step-by-Step Conversion Algorithm

Step 1: Convert Oral Hydromorphone to Oral Morphine Equivalents

• Oral hydromorphone 4 mg equals approximately 20-30 mg oral morphine using the standard NCCN conversion ratio of 5-7:1 (hydromorphone is 5-7 times more potent than morphine). 1
• The CDC conversion factor indicates 1 mg hydromorphone = 4 mg morphine in MME terms, which would yield 16 mg oral morphine equivalent. 1
• For practical purposes, use 20-24 mg oral morphine as the midpoint estimate for 4 mg oral hydromorphone. 1

Step 2: Convert Oral Morphine to IV Morphine

• The oral-to-IV morphine ratio is 3:1, meaning oral morphine has approximately one-third the potency of IV morphine due to first-pass metabolism. 1
• Divide the oral morphine dose by 3 to obtain the IV morphine equivalent. 1
• Using 20-24 mg oral morphine: 20-24 mg ÷ 3 = 6.7-8 mg IV morphine. 1

Step 3: Account for Incomplete Cross-Tolerance

• When converting between opioids, reduce the calculated dose by 25-50% to account for incomplete cross-tolerance if pain is well-controlled. 1
• If pain is poorly controlled, the calculated dose may be used unchanged or increased by up to 25%. 1
• For a conservative approach with well-controlled pain: 6.7-8 mg IV morphine × 0.5-0.75 = 3.4-6 mg IV morphine. 1
• For poorly controlled pain or direct conversion: use the full 6.7-8 mg IV morphine. 1

Alternative Direct Conversion Method

• Using the direct IV hydromorphone-to-IV morphine ratio of 5-7:1, first convert oral hydromorphone to IV hydromorphone, then to IV morphine. 1, 2
• Oral-to-IV hydromorphone ratio is approximately 5:1, so 4 mg oral hydromorphone = 0.8 mg IV hydromorphone. 1, 3
• IV hydromorphone-to-IV morphine ratio is 5-7:1, so 0.8 mg IV hydromorphone × 6 (midpoint) = 4.8 mg IV morphine. 1, 2
• After applying the 25-50% cross-tolerance reduction: 2.4-3.6 mg IV morphine for well-controlled pain. 1

Practical Clinical Recommendation

Start with 5-8 mg IV morphine for direct conversion without cross-tolerance reduction, or 3-5 mg IV morphine if applying a 50% cross-tolerance reduction. 1

Breakthrough Dosing

• Prescribe breakthrough IV morphine at 10-20% of the total 24-hour dose, available every 1-4 hours as needed. 1
• If the patient was taking 4 mg oral hydromorphone every 4-6 hours (16-24 mg/day oral hydromorphone), the total daily IV morphine equivalent would be 20-32 mg/day. 1
• Breakthrough dose: 2-6 mg IV morphine every 1-4 hours PRN. 1

Critical Safety Considerations

• Monitor closely for respiratory depression, especially during the first 24-48 hours after conversion, as individual patient responses vary significantly. 2
• Reassess at peak effect: 15 minutes for IV morphine. 2
• If more than 3-4 breakthrough doses are required per day, increase the scheduled baseline dose by 25-50% rather than continuing frequent PRN dosing. 1, 2
• In renal impairment (CrCl <30 mL/min), avoid morphine entirely due to accumulation of toxic metabolites (morphine-3-glucuronide and morphine-6-glucuronide). 1

Common Pitfalls to Avoid

• Do not use the same conversion ratio in reverse—converting from morphine back to hydromorphone requires different calculations. 1
• Conversion ratios are approximate guides; significant variation exists across institutional tools, particularly for hydromorphone conversions (variance of 4.06 ± 1.2 mg in oral-to-IV hydromorphone ratios). 4
• Do not forget to account for incomplete cross-tolerance—this is the most common cause of overdosing during opioid rotation. 1
• Research evidence suggests actual clinical conversion ratios may differ from textbook values; one study found IV hydromorphone-to-oral morphine equivalent ratio of 1:11.46, which is higher than traditional estimates. 3