Pharmacokinetics of Penicillin G in Very-Low-Birth-Weight Neonates

Abstract

Data on the pharmacokinetics (PKs) of penicillin G (PEN) in neonates date back to the 1970s and do not include data for very-low-birth-weight (VLBW) neonates. The aim of this study was to describe the steady-state PKs and to establish an optimal regimen for the dosing of PEN in neonates with gestational ages of less than 28 weeks and birth weights of less than 1,200 g. Two PEN dosing regimens were studied: 50,000 IU (30 mg)/kg of body weight every 12 h (q12h) (group 1; n ‫؍‬ 9) and 25,000 IU (15 mg)/kg q12h (group 2; n ‫؍‬ 9). Samples for PK analysis were drawn before the injection of PEN and at 2 and 30 min and 1.5, 4, 8, and 12 h after intravenous injection of the third to eighth PEN doses. The PEN concentration was measured by a highperformance liquid chromatography with UV detection technique. The median peak and trough concentrations of PEN were 147 g/ml (lower and upper quartiles, 109 and 157 g/ml, respectively) and 7 g/ml (lower and upper quartiles, 5 and 13 g/ml, respectively) after administration of the dose of 50,000 IU and 59 g/ml (lower and upper quartiles, 53 and 78 g/ml, respectively) and 3 g/ml (lower and upper quartiles, 3 and 4 g/ml, respectively) after administration of the dose of 25,000 IU. The PEN half-life (median and lower and upper quartiles for group 1, 3.9 h and 3.3 and 7.0 h, respectively; median and lower and upper quartiles for group 2, 4.6 h and 3.8 and 5.6 h, respectively) was longer in VLBW neonates than in adults and term infants. PEN renal clearance correlated with creatinine clearance (R 2 ‫؍‬ 0.309596; P ‫؍‬ 0.038). Only a median of 34% (lower and upper quartiles, 28 and 37%, respectively) of the administered dose was excreted in urine within the following 12 h. We conclude that in VLBW infants a PEN dose of 25,000 IU (15 mg)/kg q12h is safe and sufficient to achieve serum concentrations above the MIC 90 for group B streptococci for the entire dosing interval.Antibiotics are widely used in neonatal intensive care units (NICUs), and their widespread use has been associated with the development of antibiotic resistance. These developments have led to the preferred use of antibiotics known or assumed to have lower potentials for the selection of resistant microorganisms (22).Penicillin G (PEN) is a safe and narrow-spectrum antibiotic that, in combination with gentamicin, is recommended for use for the empirical therapy of neonatal sepsis (31). It has many advantages over wide-spectrum penicillins and cephalosporins. First, it has demonstrated favorable efficacy against the majority of organisms that cause neonatal sepsis (14, 27); second, it is well tolerated and does not cause allergic reactions in neonates; third, compared to other beta-lactam antibiotics, penicillin has the least effect on the development of resistance by gram-negative bacteria (9); and fourth, narrow-spectrum penicillins have a minimal effect on the normal bowel colonization in neonates and young infants (4, 17).The currently recommended PEN dosage for infants born at less than 29 weeks of gestation is 25,000...

Clinical pharmacokinetics of penicillins in the neonate: a review of the literature

“…The half-life (t ½ ) decreased from 3.2 h in the first week of life to 1.4 h in week 3. A study in 18 very low birth weight (VLBW) neonates confirmed that the t ½ in VLBW neonates is longer (4.2 h), and these authors concluded that 15 mg kg −1 12 h −1 results in serum concentrations above the minimum inhibitory concentration for 90% of group B streptococci strains (MIC 90 ) [6].…”

“…There have been three separate studies on benzylpenicillin (penicillin G) [5][6][7] ( Table 1). The first detailed study of the PK of penicillin in neonates [5] was performed in the early 1970s in 47 newborn infants (no details are given of the gestation except that the group included both preterm and term neonates).…”

Blood Loss Related to Participation in Pharmacokinetic Study in Preterm Neonates

“…The control group consisted of 35 gestational age-, postnatal age-and birth weight-matched neonates who had not participated in a PK study. Results: We did not observe significant differences in 112 that extra blood loss of up to 2.3 ml/kg over 12 h due to participation in a pharmacokinetic (PK) study [3] does not exert adverse influence on hemodynamic stability and/or increase the risk of complications in VLBW neonates.…”

“…1,200 g and aged ! 5 days, needing treatment with penicillin-G and gentamicin for risk of early onset sepsis [3] .…”

“…A prespecified volume of 0.3 ml of blood per sample was drawn before and at 2 min, 30 min, 1.5 h, 4 h, 8 h and 12 h after the third to eighth intravenous injection of penicillin-G (study dose) [3] . The study dose for the control infant, and hence the period of data collection, was the same as for the respectively matched study infant.…”