What is an appropriate opioid substitution for a patient with metastatic melanoma undergoing chemotherapy who takes 30 mg of hydrocodone (opioid analgesic) daily and now requires an alternative due to hydrocodone unavailability?

Appropriate Opioid Substitution for Hydrocodone in Cancer Pain

Prescribe immediate-release oxycodone 10 mg total daily in divided doses (Option A). This represents the correct equianalgesic conversion from 30 mg daily hydrocodone, accounting for the 1.5-2x potency ratio and the mandatory 25-50% dose reduction for incomplete cross-tolerance 1.

Equianalgesic Conversion Calculation

The conversion from hydrocodone to oxycodone requires understanding relative potencies:

• Oxycodone is 1.5-2 times more potent than hydrocodone 2, 3
• Using a conservative 1.5x ratio: 30 mg hydrocodone ÷ 1.5 = 20 mg oxycodone equivalent 1
• Critical safety step: Reduce by 25-50% for incomplete cross-tolerance when switching opioids 2, 1
• Final dose: 20 mg × 0.5 = 10 mg oxycodone daily 1

Why Other Options Are Incorrect

Option B (ibuprofen) is completely inappropriate:

• NSAIDs alone cannot substitute for chronic opioid therapy in cancer pain 2
• This patient requires WHO Step III opioids for metastatic melanoma pain 2
• Abrupt opioid discontinuation risks withdrawal symptoms 1

Option C (hydrocodone 20 mg) is impossible:

• The question explicitly states hydrocodone is unavailable 1

Option D (Tylenol) is inadequate:

• Acetaminophen alone cannot replace chronic opioid therapy for moderate-to-severe cancer pain 2
• Would result in severe underdosing and potential withdrawal 1

Option E (oxycodone 40 mg) represents dangerous overdosing:

• This is 4x the correct converted dose 1
• Ignores the mandatory dose reduction for opioid switching 2
• Significantly increases risk of respiratory depression and CNS toxicity 2

Practical Dosing Protocol

Divide the 10 mg total daily dose appropriately:

• Administer as immediate-release oxycodone 5 mg every 12 hours 1
• Alternatively: 2.5 mg every 6 hours for more frequent dosing 2
• Provide breakthrough doses of 1-2 mg (10-20% of total daily dose) for incident pain 2, 1

Special Considerations in This Clinical Context

This patient has active infection (port-site erythema, fever, leukocytosis):

• Fever can accelerate transdermal absorption—avoid fentanyl patches 1
• Monitor closely for opioid-related side effects during acute illness 1
• Immediately initiate prophylactic bowel regimen with stimulant laxatives 2, 1

Oxycodone advantages in this scenario:

• Oral bioavailability 60-87% vs morphine's lower bioavailability 3
• More predictable metabolism than morphine, easier titration 3
• Shorter time to stable plasma levels (24 hours vs 2-7 days for morphine) 3
• Somewhat less nausea and hallucinations than morphine 3

Critical Pitfalls to Avoid

Underdosing during conversion:

• Inadequate analgesia leads to breakthrough pain and potential withdrawal 1
• Always calculate full equianalgesic dose first, then reduce for safety 1

Overdosing from incorrect conversion:

• Option E (40 mg) represents this error—using direct 1:1 conversion without dose reduction 1
• Can cause respiratory depression, especially in acute illness 2

Forgetting incomplete cross-tolerance:

• Opioid receptors don't respond identically to different opioids 2
• The 25-50% reduction is mandatory, not optional 2, 1

2, 1, 3