Codeine and morphine blood concentrations increase during blood loss.

Area of Science:

• Pharmacology
• Physiology
• Toxicology

Background:

• Plasma volume expands during significant blood loss through extravascular fluid transfer.
• Drugs within this fluid can shift blood concentrations, impacting efficacy and safety.
• Understanding these shifts is crucial for managing patients with hemorrhage.

Purpose of the Study:

• To investigate the impact of standardized exsanguination on codeine and morphine concentrations in rat whole blood.
• To determine if blood loss influences the pharmacokinetics of codeine and its primary metabolite.

Main Methods:

• Oral administration of 5 mg codeine to rats.
• Standardized blood withdrawal (0.8 mL at 10-min intervals for 70 min) in the exsanguination group.
• Control group underwent blood withdrawal only at the start and end of the 70-min period.
• Measurement of codeine and morphine concentrations in whole blood.

Main Results:

• In exsanguinated rats, the final/initial concentration ratios for codeine and morphine increased significantly (1.28 and 1.41, respectively).
• Control rats showed concentration ratios close to 1 (0.70 for codeine, 0.88 for morphine), indicating minimal change without significant blood loss.
• Statistical analysis confirmed a significant effect of blood loss on both codeine and morphine levels (p < 0.05).

Conclusions:

• Exsanguination significantly alters blood drug concentrations.
• Blood loss can lead to an accumulation of codeine and morphine in circulation.
• These findings highlight the importance of considering hemorrhage in drug level monitoring.