To assess methadone analgesia, adverse effects, and calculation method of equianalgesic doses with oral morphine.
Methadone was administered to 21 opioid-tolerant cancer patients because of pain (numerical rating scale [NRS] > 5) on morphine (ten patients), transdermal fentanyl (TF; four patients), morphine, ketamine, and TF (one patient), tramadol (one patient), pethidine (one patient), pain with drowsiness on morphine with ketamine (three patients), and pain with nausea on morphine (one patient). Dose ratios of equivalent daily dose of oral morphine (ddom) to daily dose of oral methadone (ddomet) were 4:1 (ddom to 100 mg), 6:1 (101-300 mg), 12:1 (301-1,000 mg), and 20:1 (over 1,000 mg). Previous opioid treatment was stopped completely (stop-start approach) in 19 patients; two received methadone and other opioids. The mean ddom before switch was 812 +/- 486 mg. Methadone was administered regularly three times daily; 20 patients received oral methadone, one patient received rectal suppositories. Breakthrough pain was treated with methadone (half of regular dose), morphine, fentanyl, metamizol, ketoprofen, or ketamine.
Mean time of methadone treatment was 38.3 +/- 27.1 days (range 3-95 days), mean daily doses: start 48.1 +/- 19.7 mg, maximal 148.5 +/- 104.1 mg, treatment completion 131.1 +/- 104.3 mg. Good analgesia (NRS < 4) was observed in 11 patients, partial (NRS 4-5) in nine patients, and unsatisfactory (NRS > 5) in one patient. Adverse effects such as drowsiness (six patients), constipation (six patients), nausea and vomiting (two patients), sweating (two patients), and respiratory depression (one patient) the last one resolved by methadone cessation and naloxone.
Results confirmed high analgesic efficacy, acceptable methadone adverse event profile, safety, and effectiveness of ddom to ddomet dose calculation method.