Moxalactam epimer kinetics in children.

Area of Science:

• Pharmacokinetics and Drug Metabolism
• Pediatric Infectious Diseases
• Antibiotic Therapy

Background:

• Moxalactam is a beta-lactam antibiotic used for severe infections.
• Understanding the pharmacokinetic differences between its R and S epimers is crucial for optimizing treatment.
• Pediatric populations may exhibit unique drug metabolism profiles.

Purpose of the Study:

• To investigate the pharmacokinetic profiles of R and S epimers of moxalactam in pediatric patients.
• To compare the total body clearance and apparent volume of distribution between the two epimers.
• To assess the implications of pharmacokinetic variability for clinical monitoring.

Main Methods:

• Single intravenous doses of moxalactam (50 mg/kg) administered to 12 pediatric patients (8-45 months) with cellulitis or epiglottitis.
• Serum concentrations quantified using high-pressure liquid chromatography (HPLC).
• Pharmacokinetic parameters including clearance, volume of distribution, and half-life calculated for R and S epimers.

Main Results:

• The R epimer exhibited significantly higher total body clearance (P < 0.004) and apparent volume of distribution compared to the S epimer.
• Total body clearance ranged from 29.01 to 183.7 ml/min/m2 for R, 19.00 to 79.95 ml/min/m2 for S, and 23.34 to 113.6 ml/min/m2 for R+S.
• Mean elimination half-lives were approximately 2.04 hr for R, 2.26 hr for S, and 2.24 hr for R+S.

Conclusions:

• The increased incidence of the more active R epimer and substantial interpatient variability (up to 500%) in moxalactam clearance highlight potential therapeutic challenges.
• Monitoring of serum and cerebrospinal fluid concentrations may be warranted in pediatric patients with severe, unresponsive central nervous system infections treated with moxalactam.
• These findings underscore the need for individualized dosing strategies in pediatric populations to ensure therapeutic efficacy and minimize toxicity.