What is the equivalent subcutaneous dose of hydromorphone (every 4 hours) for a patient currently taking oral hydromorphone 0.5 mg (four times a day)?

Converting Oral Hydromorphone to Subcutaneous Dosing

When converting from oral hydromorphone 0.5 mg QID to subcutaneous hydromorphone Q4H, use a conversion ratio of 5:1 (oral to parenteral), resulting in a subcutaneous dose of 0.1 mg every 4 hours.

Conversion Calculation

• Calculate the total daily oral hydromorphone dose: 0.5 mg × 4 times per day = 2 mg/day oral hydromorphone 1
• Apply the appropriate oral-to-parenteral conversion ratio of 5:1 (oral morphine equivalent to parenteral hydromorphone) 1
• This means the total daily subcutaneous dose should be 2 mg ÷ 5 = 0.4 mg/day 2
• Since the subcutaneous dose will be given every 4 hours (6 times per day), divide the daily dose by 6: 0.4 mg ÷ 6 = 0.067 mg, rounded to 0.1 mg subcutaneous hydromorphone every 4 hours 1

Evidence Supporting Conversion Ratios

• The FDA drug label for hydromorphone indicates that when converting from oral to parenteral routes, a ratio of approximately 5:1 should be used 1
• The National Comprehensive Cancer Network guidelines support this conversion ratio, noting that oral hydromorphone has approximately one-fifth the potency of parenteral hydromorphone 2
• When converting between routes of administration, the bioavailability differences must be accounted for, as parenteral administration bypasses first-pass metabolism 3

Special Considerations

• Initial dosing should be conservative when converting between routes, as individual patient response may vary 1
• For patients with hepatic or renal impairment, lower starting doses may be required due to altered pharmacokinetics 1
• Monitor the patient closely after conversion for both pain control and potential adverse effects 2
• Rescue medication may be needed during the transition period until stable analgesia is achieved 2

Potential Pitfalls and Caveats

• Avoid using the same dose for both oral and subcutaneous routes, as this could lead to overdosing due to the higher bioavailability of subcutaneous administration 1
• Be aware that conversion ratios are approximate guides and clinical judgment is essential 2
• Patients may require dose adjustments based on their response to the initial conversion 1
• The subcutaneous route provides more consistent absorption compared to oral administration, which may affect the timing and intensity of pain relief 3

Monitoring After Conversion

• Assess pain control 15 minutes after subcutaneous administration 4
• If pain control is inadequate, consider increasing the dose by 25-50% 2
• Monitor for common opioid-related adverse effects such as respiratory depression, constipation, and nausea 4