What is the intravenous (IV) dose of hydromorphone equivalent to morphine 4 milligrams (mg) IV?

Hydromorphone IV Dose Equivalent to Morphine 4 mg IV

The IV hydromorphone dose equivalent to morphine 4 mg IV is 0.8 mg, based on the standard 5:1 conversion ratio (10 mg IV morphine = 2 mg IV hydromorphone). 1, 2

Conversion Calculation

• Using the National Comprehensive Cancer Network guideline conversion ratio of 5:1 for IV morphine to IV hydromorphone, 4 mg of IV morphine converts to 0.8 mg of IV hydromorphone 1, 2
• This calculation is straightforward: (4 mg morphine ÷ 10 mg morphine) × 2 mg hydromorphone = 0.8 mg hydromorphone 1

Supporting Evidence and Nuances

The 5:1 conversion ratio is consistently supported across multiple guidelines, though some research suggests slightly different potency ratios:

• The CDC Guideline for Prescribing Opioids uses a conversion factor of 4:1 when calculating morphine milligram equivalents (1 mg hydromorphone = 4 mg morphine), which would yield 1 mg hydromorphone for 4 mg morphine 3
• Research data indicates IV hydromorphone may be 8.5 times as potent as IV morphine on a milligram basis, which would suggest an even lower dose of approximately 0.47 mg 4
• However, the National Comprehensive Cancer Network's 5:1 ratio (yielding 0.8 mg) represents the most widely accepted clinical standard and is specifically designed for safe opioid conversion in practice 1, 2

Clinical Application Considerations

When implementing this conversion, apply a 25-50% dose reduction if the patient was well-controlled on morphine to account for incomplete cross-tolerance:

• If morphine 4 mg IV was providing effective pain control, reduce the calculated hydromorphone dose (0.8 mg) by 25-50%, resulting in 0.4-0.6 mg IV hydromorphone 1
• If morphine was ineffective in controlling pain, you may begin with 100% of the equianalgesic dose (0.8 mg) or increase by 25% (1 mg) 1

Important Caveats

• Conversion ratios are approximate guides, and clinical judgment is essential when converting between opioids, as individual patient variability exists 3
• Hydromorphone has a quicker onset of action compared to morphine, which may affect timing of pain relief assessment 2
• Monitor patients closely after conversion for both pain control and adverse effects, including respiratory depression, sedation, nausea, and constipation 2, 5
• The smaller volume required for hydromorphone administration (due to higher potency) may be beneficial in certain clinical scenarios such as patient-controlled analgesia 3