In vitro activity: Cefdinir, a new oral 2-amino-5-thiazolyl cephalosporin, inhibits the luminol-amplified chemiluminescence (LACL) response of human neutrophils stimulated by PMA but not opsonized zymosan, in a concentration-dependent but not time-dependent manner. Cefdinir inhibits LACL generation in cell-free systems consisting of H2O2, NaI, and either horseradish peroxidase or amyeloperoxidase-containing neutrophil extract. Cefdinir impairs LACL response induced by the calcium ionophore A23187 and FMLP, and this impairment is increased in cytochalasin B-treated neutrophils. Cefdinir directly inhibits the activity of myeloperoxidase-containing neutrophil extract released into the extracellular medium during neutrophil stimulation by soluble mediators, but has no effect on that released into the phagolysosome during phagocytosis. Cefdinir demonstrates excellent activity against a wide range of gram-positive and gram-negative bacteria. Cefdinir is resistant to a broad variety of β-lactamases and exhibits a β-lactam stability profile generally better than those observed with cefaclor and cefuroxime. Cefdinir elimination is primarily mediated by the kidney. Cefdinir interacts with the dipeptide transporters PEPT1 and PEPT2. Cefdinir tubular reabsorption is substantial, that Cefdinir tubular secretion is inhibitable by probenecid, and that this secretion is probably mediated by the renal organic anion secretory pathway.