Neonatal Intensive Care Drug Manual

Preterm neonates have reduced azithromycin clearance and increased volume of distribution compared to older children. The estimated half-life is approximately 58 hours for a typical 1 kg neonate. Once administered, very little of azithromycin resides in the plasma and the vast majority of azithromycin accumulates intracellularly leading to a prolonged elimination t_1/2 and extended mean residence time (MRT). These characteristics favour administering higher dosage regimens of azithromycin. For effective Ureaplasma eradication, the plasma concentration of free unbound azithromycin must be maintained above the minimum inhibitory concentration that is required to inhibit 50% (MIC₅₀) of Ureaplasma. Multiple dose administration of 10 mg/kg/day for 3 days azithromycin is inadequate to maintain azithromycin plasma concentrations above the MIC₅₀. On the other hand, a dosage regimen of 20 mg/kg/day for 3 days would be sufficient to maintain azithromycin plasma concentration above the MIC₅₀.¹⁶