Overview
This lecture covers opioid rotation and dose equivalencies, focusing on safely switching patients from one opioid to another, accounting for individual factors and clinical scenarios.
Reasons for Opioid Rotation
- Different clinical situations (acute vs. chronic) may require switching opioids.
- Drug availability may vary based on institution or location.
- Genetic polymorphisms (e.g., CYP450 2D6 variants) can affect opioid metabolism and effectiveness.
- Patients may experience variable analgesic response or adverse effects with certain opioids.
- Some opioids require metabolic activation (e.g., codeine, hydrocodone).
Opioid Dose Equivalency Principles
- Dose equivalency tables are guides; IM/IV to PO ratios are often about 1:3 for morphine.
- Cross-tolerance and metabolic differences factor into switching; always reduce calculated dose when switching.
- Long-acting opioids (e.g., MS Contin) may require shorter dosing intervals for some patients.
- Fentanyl patches and other formulations have unique onset and absorption features.
Steps for Opioid Conversion
- Calculate the total daily dose of current opioid (long-acting plus immediate release).
- Use equivalency charts to determine the new opioid's equivalent dose.
- Reduce calculated dose by 25–50% for most opioids when switching (75–90% for methadone).
- Consider available formulations and appropriate dosing intervals for the new opioid.
- Methadone has unique pharmacokinetics and higher risk for drug interactions and toxicity.
Breakthrough Pain Management
- Breakthrough (rescue) dose = 5–15% of the total daily opioid dose, given as needed.
- Frequent need for breakthrough dosing indicates inadequate long-acting regimen.
- Immediate-release opioids are for acute pain or breakthrough, not primary chronic pain control.
Clinical Example Summary
- Assess daily opioid intake (sum scheduled and breakthrough doses).
- Convert to new opioid using equivalency ratio; adjust dose downward for safety.
- Divide new total daily dose into appropriate dosing intervals/formulations.
- Prescribe breakthrough dosing based on percentage of new total daily dose.
Key Terms & Definitions
- Opioid Rotation — Switching from one opioid to another to improve efficacy or reduce side effects.
- Dose Equivalency — The calculated equivalent dose of another opioid providing similar analgesic effect.
- CYP450 2D6 — Liver enzyme involved in metabolism/activation of certain opioids (e.g., codeine).
- Breakthrough Pain — Acute pain episodes occurring despite baseline chronic pain control.
- Cross-Tolerance — Partial tolerance to other opioids developed after chronic exposure to one opioid.
Action Items / Next Steps
- Review the opioid dose equivalency table provided in course materials.
- Practice opioid conversion calculations using clinical examples.
- Be prepared to consider patient-specific factors (genetics, renal/liver function, drug interactions) when managing opioids.