PK/PD-guided ceftazidime–avibactam dosing for multidrug-resistant Pseudomonas aeruginosa infection in a preterm infant with chylothorax and ascites: a case report

Background Multidrug-resistant Pseudomonas aeruginosa (MDR-PA) infection in preterm infants is associated with high mortality, and treatment options are limited. Ceftazidime-avibactam (CAZ-AVI) is a novel β-lactam/β-lactamase inhibitor combination, but data on its pharmacokinetic/pharmacodynamic (PK/PD)-guided use in preterm infants are scarce. Methods We report a 33-week preterm infant with congenital chylothorax/ascites complicated by MDR-PA infection. Antimicrobial susceptibility testing revealed resistance to meropenem (MIC > 16 μg/mL) and ceftazidime (MIC > 32 μg/mL) but sensitivity to CAZ-AVI (MIC = 4 μg/mL). A PK/PD-guided regimen of CAZ-AVI 40–50 mg/kg (based on the ceftazidime component, every 8 h, prolonged infusion ≥2 h) was administered to achieve a %fT > MIC target of ≥ 70%, considering the preterm infant’s immature renal function and increased volume of distribution. Results After initiation of CAZ-AVI, high-sensitivity C-reactive protein (hs-CRP) decreased from 30.00 mg/L to 7.21 mg/L within 5 days and normalized by day 7. Thoracic and abdominal drainage volumes declined significantly. The infant was successfully weaned from mechanical ventilation and discharged with clinical recovery. No drug-related adverse events were observed. Conclusion PK/PD-based individualized CAZ-AVI therapy achieved a favorable clinical outcome in this preterm infant with MDR-PA infection. A dosing strategy targeting %fT> MIC ≥ 70% appears feasible and safe in neonates. This case provides quantitative PK/PD support for CAZ-AVI dosing in preterm infants, a population with limited existing evidence.