Peak plasma concentrations after oral morphine: a systematic review

Area of Science:

• Pharmacokinetics
• Drug Absorption and Metabolism
• Clinical Pharmacology

Background:

• Understanding oral morphine pharmacokinetics is crucial for effective pain management.
• Variability in drug absorption can impact therapeutic outcomes.
• Previous studies have yielded diverse results regarding oral morphine bioavailability.

Purpose of the Study:

• To systematically review pharmacokinetic data for oral morphine formulations.
• To analyze maximum plasma concentration (Cmax) and time to Cmax (Tmax).
• To identify factors contributing to pharmacokinetic variability.

Main Methods:

• Systematic review of 69 studies.
• Inclusion of data from 2146 subjects (454 patients, 1692 healthy volunteers).
• Analysis of Cmax and Tmax for various oral morphine formulations (immediate-release, controlled-release, solutions, tablets, different salts).

Main Results:

• Healthy volunteer data mirrored patient data but showed less variability.
• No significant accumulation of morphine observed with single versus multiple doses.
• Immediate-release morphine: no difference in dose-corrected Cmax or Tmax between solutions and tablets, or salts.
• Controlled-release formulations: minimal brand differences; once-daily formulations showed longer Tmax in fed vs. fasted states.
• No analytical method (RIA vs. HPLC) influenced results.

Conclusions:

• Oral morphine formulations exhibit predictable pharmacokinetic profiles.
• Formulation type (immediate vs. controlled-release) and dosing frequency (once-daily) are key factors influencing absorption.
• Food intake significantly impacts Tmax for once-daily formulations.
• Analytical method does not affect pharmacokinetic parameter determination.