Therapeutic Drug Monitoring of Moxifloxacin to Guide Treatment of Mycoplasma hominis Meningitis in an Extremely Preterm Infant

Mycoplasma hominis (M hominis) is a rare cause of neonatal bacterial meningitis. Treatment can be challenging because of M hominis' intrinsic antibiotic resistance and the difficulty in accessing antimicrobial susceptibility testing. In this report, we describe an extremely preterm male infant with seizures who had a subsequent diagnosis of M hominis meningitis. Because of severity of illness, doxycycline (4 mg/kg IV every 24 hours) and moxifloxacin (5 mg/kg IV every 24 hours) were started empirically. Repeat cerebrospinal fluid cultures were negative and showed decreasing pleiocytosis. Given the concentration-dependent killing of moxifloxacin and concern for endovascular infection from a concomitant cerebral venous sinus thrombosis, serum concentrations of moxifloxacin were obtained to estimate pharmacokinetic and pharmacodynamic parameters. These were compared to the targets described in other case reports of M hominis meningitis. The maximum serum concentration (Cmax) was 2.5 mg/L, volume of distribution was 2.2 L/kg, clearance was 0.18 L/kg/hr, terminal half-life was 8.6 hours, and area-under-the-concentration-time curve (AUC) was 28.1 mg•hr/L. Using the range of minimum inhibitory concentrations (MICs) reported in the literature, the estimated Cmax/MIC for this patient was 21 to 158 (target Cmax/MIC: >10) and AUC/MIC was 234 to 1757 (target AUC/MIC: ≥100). Doxycycline and moxifloxacin were continued for 6 weeks. No adverse events to moxifloxacin or doxycycline were observed in the NICU. This report describes the successful treatment of M hominis neonatal meningitis and adds to the knowledge of pharmacokinetic and pharmacodynamic parameters of moxifloxacin in neonates. Additional data will help to confirm the role for routine therapeutic drug monitoring of moxifloxacin in neonates.