Opioid switching from transdermal fentanyl to oral methadone in patients with cancer pain.

BACKGROUND

Patients with cancer often are rotated from other opioids to methadone to improve the balance between analgesia and side effects. To the authors' knowledge, no clear guidelines currently exist for the safe and effective rotation from transdermal fentanyl to methadone.

METHODS

The authors evaluated a protocol for switching opioid from transdermal fentanyl to oral methadone in 17 patients with cancer. Reasons for switching were uncontrolled pain (41.1% of patients) and neurotoxic side effects (58.9% of patients). Methadone was initiated 8-24 hours after fentanyl withdrawal, depending on the patient's previous opioid doses (from < 100 microg per hour to > 300 microg per hour). The starting methadone dose was calculated according to a 2-step conversion between transdermal fentanyl:oral morphine (1:100 ratio) and oral morphine:oral methadone (5:1 ratio or 10:1 ratio). The correlation between previous fentanyl dose and the final methadone dose or the fentanyl:methadone dose ratio was assessed by means of Pearson and Spearman correlation coefficients (r), respectively. A Friedman test was used to compare pain intensity before and after the switch and the use of daily rescue doses.

RESULTS

Opioid rotation was fully or partially effective in 80% and 20%, respectively, of patients with somatic pain. Neuropathic pain was not affected by opioid switching. Delirium and myoclonus were reverted in 80% and 100% of patients, respectively, after opioid switching. A positive linear correlation was obtained between the fentanyl and methadone doses (Pearson r, 0.851). Previous fentanyl doses were not correlated with the final fentanyl:methadone dose ratios (Spearman r, - 0.327).

CONCLUSIONS

The protocol studied provided a safe approach for switching from transdermal fentanyl to oral methadone, improving the balance between analgesia and side effects in patients with cancer.