The oral-to-intravenous equianalgesic ratio of morphine based on plasma concentrations of morphine and metabolites in advanced cancer patients receiving chronic morphine treatment.
To provide additional pharmacokinetic evidence for the oral-to-parenteral relative potency ratio of 1:2 to 1:3 for chronic morphine use in a palliative care setting, we determined the plasma concentrations of morphine and its major metabolites, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), in hospitalized advanced cancer patients maintained on long-term oral or intravenous morphine. There were significant linear correlations between daily doses of morphine and plasma concentrations (molar base) of morphine, M3G and M6G for both routes of administration. The oral-to-intravenous relative ratios of the regression coefficients were 2.9 for morphine and 1.8 for morphine + M6G. The morphine kinetic variables were not significantly influenced by any hepato-renal biochemical markers. These results support the commonly used oral-to-intravenous relative potency ratio of 1:2 to 1:3 in patients with cancer pain receiving chronic morphine treatment.
Takahashi
Masahiko
M
Division of Pain Control, Department of Anesthesiology and Emergency Medicine, Tohoku University Postgraduate Medical School, 1-1 Seiryo, Aoba-ku, Sendai 980-8574, Japan. m-takaha@mail.cc.tohoku.ac.jp
Ohara
Takeshi
T
Yamanaka
Hiroyuki
H
Shimada
Akira
A
Nakaho
Toshimichi
T
Makoto
Yamamuro
Y
D000284:Administration, Oral; D000368:Aged; D000701:Analgesics, Opioid / Q000008:administration & dosage* / Q000097:blood*; D002908:Chronic Disease; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007263:Infusions, Parenteral; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage* / Q000097:blood*; D009022:Morphine Derivatives / Q000097:blood; D009369:Neoplasms / Q000097:blood / Q000150:complications*; D010146:Pain / Q000097:blood / Q000188:drug therapy* / Q000209:etiology; D010166:Palliative Care
D000701:Analgesics, Opioid; D009022:Morphine Derivatives; C035349:morphine-6-glucuronide; D009020:Morphine; C018108:morphine-3-glucuronide