The oral-to-intravenous equianalgesic ratio of morphine based on plasma concentrations of morphine and metabolites in advanced cancer patients receiving chronic morphine treatment

Masahiko Takahashi, Takeshi Ohara, Hiroyuki Yamanaka, Akira Shimada, Toshimichi Nakaho, Makoto Yamamuro

Research output: Contribution to journalArticle

16 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)673-678
Number of pages6
JournalPalliative Medicine
Volume17
Issue number8
Publication statusPublished - 2003

Keywords

  • Morphine pharmacokinetics
  • Oral/intravenous relative potency ratios for morphine

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

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