Serum levels following epidural administration of morphine and correlation with relief of postsurgical pain

S. J. Weddel, R. R. Ritter

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79 Scopus citations

Abstract

This study was undertaken to determine the serum levels of free morphine base resulting from the epidural administration of morphine, and to correlate these serum levels with analgesic effect. Results from twenty-one patients are presented. Following major surgery with bupivacaine or lidocaine continuous epdidural block as the primary anesthetic, 5 or 10 mg/70 kg body weight of preservative-free morphine sulfate was administered through the epidural catheter when the patient noted the onset of post-surgical pain. Serum morphine levels were determined at intervals between 5 and 240 min post injection using a liquid chromatography technique with electrochemical detection, and analgesic effectiveness was assessed using a linear pain analogue scale and the subjective response of the patient. The mean peak serum level in the patients receiving 5 mg/70 kg was 28.0 ± 20.6 ng/ml with mean serum levels declining to 2.1 ± 1.6 ng/ml over the four-hour post injection period. The patients receiving 10 mg/70 kg had a mean peak serum level of 49.7 ± 35.6 ng/ml with mean serum levels declining to 5.4 ± 4.8 ng/ml over the 4-hour postinjection period. Average onset of significant analgesia was 15 min postinjection. Duration of adequate analgesia varied from 4 hours to several days, the mean being 37.9 hours for those receiving 5 mg/70 kg, and 51.6 hours for those receiving 10 mg/70 kg. Side effects included pruritis, ameliorated with diphenhydramine, and urinary retention. Somnolence and slowing of respiratory rate which developed in one patient were reversed with naloxone without notable effect on the duration or intensity of the analgesic response to the epidural morphine. This study demonstrates the analgesic effectiveness of and the serum morphine levels consequent to the epidural administration of morphine, and supports the concept of a selective spinal analgesic action.

Original languageEnglish (US)
Pages (from-to)210-214
Number of pages5
JournalAnesthesiology
Volume54
Issue number3
DOIs
StatePublished - 1981
Externally publishedYes

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine

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