107 PCN Methadone Notes
- Convert PO Methadone to IV Methadone:
- Total Methadone Dose/2
- Infused over 24 hrs or divided q6-8 hr
Convert 24 hour Oral Morphine Equivalent (OME) to equianalgesic Morphine dose:
| OME | Ratio OME to 24 hr PO Methadone dose |
| <60 | “opioid naïve” – Methadone 2.5 mg bid or tid |
| 60-200 | 10:1 (less than 65 years old) |
| >200 | 20:1 (or if greater than 65 years old) |
(consider Fixed dose Methadone of 30 mg when OME > 300)
Adjust (decrease) calculated dose of Methadone up to 50%:
- Incomplete cross tolerance
- Varied metabolism
- Imperfection of equianalgesic tables
Dose should not be increased before 5-7 days and not increased by more than 5-10 mg/day once a total daily dose of 30-40 mg has been reached
ECG evaluation for QTc prolongation based on clinical judgment
- Methadone Interactions
- CYP450 inhibition > increase effect
- Macrolides – clarithromycin, erythromycin
- diltiazem, verapamil
- ketoconazole
- itraconazole
- cyclosporine
- grapefruit juice
- CYP450 induction > decrease effect
- phenobarbital
- phenytoin
- carbamazepine
- ritonavir
- CYP450 inhibition > increase effect
Estimate of Methadone to Morphine Conversion (JPM 2008;11:1103)
- 1 mg Methadone PO = 4.7 mg Morphine PO
- 1 mg Methadone IV = 13.5 mg Morphine PO
