title: The oral-to-intravenous equianalgesic ratio of morphine based on plasma concentrations of morphine and metabolites in advanced cancer patients receiving chronic morphine treatment.
abstract: 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.
authors.affiliation: 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
authors.forename: Masahiko
authors.initials: M
authors.lastname: Takahashi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ohara
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamanaka
authors.forename: Akira
authors.initials: A
authors.lastname: Shimada
authors.forename: Toshimichi
authors.initials: T
authors.lastname: Nakaho
authors.forename: Yamamuro
authors.initials: Y
authors.lastname: Makoto
mesh_terms: 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
chemical_list: D000701:Analgesics, Opioid; D009022:Morphine Derivatives; C035349:morphine-6-glucuronide; D009020:Morphine; C018108:morphine-3-glucuronide