Aztreonam in the treatment of severe urinary tract infections in pediatric patients

Dosing Recommendations for Pediatric Patients With Renal Impairment

A treatment gap exists for pediatric patients with renal impairment. Alterations in renal clearance and metabolism of drugs render standard dosage regimens inappropriate and may lead to drug toxicity, but these studies are not routinely conducted during drug development. The objective of this study was to examine the clinical evidence behind current renal impairment dosage recommendations for pediatric patients in a standard pediatric dosing handbook. The sources of recommendations and comparisons included the pediatric dosing handbook (Lexicomp), the U.S. Food and Drug Administration-approved manufacturer's labels, and published studies in the literature. One hundred twenty-six drugs in Lexicomp had pediatric renal dosing recommendations. Only 14% (18 of 126) of Lexicomp pediatric renal dosing recommendations referenced a pediatric clinical study, and 15% of manufacturer's labels (19 of 126) described specific dosing regimens for renally impaired pediatric patients. Forty-two products had published information on pediatric renal dosing, but 19 (45%) were case studies. When pediatric clinical studies were not referenced in Lexicomp, the renal dosing recommendations followed the adult and pediatric dosing recommendations on the manufacturer's label. Clinical evidence in pediatric patients does not exist for most renal dosing recommendations in a widely used pediatric dosing handbook, and the adult renal dosing recommendations from the manufacturer's label are currently the primary source of pediatric renal dosing information.

Clinical pharmacokinetics of aztreonam

Aztreonam (azthreonam) is practically completely absorbed after intramuscular injection. After intravenous injection plasma concentrations follow a 2-compartment open model, with a t1/2 alpha of 0.20 hours. Volume of distribution at steady-state (Vdss) after intravenous or intramuscular injection is about 0.16 L/kg (0.42 L/kg for the free drug). After oral administration less than 1% of the drug is absorbed. Over a large dosage range plasma concentrations increase linearly with dose. No accumulation occurs after multiple dosing. Plasma binding in healthy subjects is about 56% and is not concentration dependent. Diffusion into tissues is generally slow, and the ratio between mean tissue and plasma concentration seems to depend mainly on the composition of the tissue. In inflamed meninges, penetration of aztreonam into CSF is more rapid than with uninflamed meninges. Diffusion through the placenta is poor, as is diffusion into breast milk. The main route of elimination of aztreonam is by the kidney, partly by active tubular excretion, but this can be inhibited by probenecid. Extrarenal clearance is probably due to excretion by the liver. Metabolism occurs to a very limited extent. Total plasma clearance in healthy adults is about 140 ml/min (8.4 L/h) or 2 ml/min/kg (0.12 L/h/kg), and terminal half-life is 1.7 hours. In children clearance is similar to that in adults when expressed as a function of bodyweight, but in neonates, especially in low birthweight infants, it is less [about 1 ml/min/kg (0.06 L/h/kg)]. In various disease states the Vdss of aztreonam is not appreciably different from that found in healthy individuals.(ABSTRACT TRUNCATED AT 250 WORDS)