Background: Many premature born neonates receive antibiotic drugs to treat infections, which are applied during active nephrogenesis. We studied the impact of clinical concentrations of gentamicin and alternatives, ceftazidime and meropenem, on ureteric branching. Methods: Mice metanephroi were dissected at embryonic day 13 and cultured in media with or without various concentrations of gentamicin, ceftazidime, or meropenem. Zero and 24 h kidney size were assessed by surface area measurements, and the ureteric tree was visualized by whole mount staining and confocal microscopy. Branching was evaluated by counting and gene expression levels of Wt1, Sox9, Bmp7, Fgf8, and Gdnf were investigated. results: A concentration of 2,000 μmol/l ceftazidime impaired ureteric development. In addition, a 4.5-fold and a 2.5-fold downregulation was noted in Fgf8 and Gdnf, respectively. No adverse effects were noted after gentamicin or meropenem treatment. No relationship was noted between surface area expansion and ureteric bud formation, but surface area at explantation related to bud count after 24 h of culture. conclusion: Ceftazidime, but not gentamicin or meropenem reduced ureteric branching in mice and suggest a role for Fgf8 and Gdnf in its mechanism. Metanephros surface area measurements can be used to reduce intra-and inter-litter variation. k idney development, leading to the formation of nephrons, starts around the 5th wk of gestation and terminates before term birth, around the 34th-36th wk of gestation. Many factors have been described to disturb this developmental process, leading to long-term problems such as hypertension and chronic kidney disease (1).One such disturbing factor may be the use of (nephrotoxic) drugs during kidney development, such as in pregnant women or neonates born before termination of nephrogenesis. Gentamicin, as well as other aminoglycosides, is widely used as part of the first line treatment of (suspected) bacterial infection in neonates to combat Gram-negative infections. Based on data from the Netherlands Perinatal Registry, 62% of neonates born before 32 wk, who can be considered the most vulnerable group, are treated with aminoglycosides (2). However, due to the fact that gentamicin is classified as a nephrotoxic drug, controversy remains on its safety as aminoglycosides have been shown to disturb kidney development and lead to a reduced nephron number in some experimental animals (3-6) and organ culture studies (7).The aim of our research was to study the impact of antibiotic treatments on nephrogenesis in a model of early nephrogenesis. Gentamicin was studied as well as clinically relevant, alternative drug treatments to compare the toxic potentials of these drugs in a clinical dose range. As alternative treatments, we chose a third generation cephalosporin, ceftazidime, and the carbapenem meropenem. These two drugs both have properties to deal with Gram-negative bacteria and have different mechanisms of action compared to gentamicin. Although beta-lactams have their own potencies to...