The aim of this study was to explore the mechanism(s) by which oral cephalosporins penetrate into human oropharyngeal mucosa, and thus, the availability of sufficient concentrations at the site of infection. Two oral cephalosporin prototypes, cephalexin (first generation) and cefixime (third generation), were administered to five healthy subjects at two different visits with a 1-week washout period. Plasma and saliva samples were collected and drug concentrations were measured using an appropriate HPLC method. The maximum plasma concentrations (Cmax) of cefixime and cephalexin were 2.97+/-0.24 microg ml(-1) and 77.65+/-18.91 microg ml(-1), respectively. These concentrations were associated with a maximum salivary concentration (CSmax) of 0.56 microg ml(-1) for cefixime and 3.34 microg ml(-1) for cephalexin. Such levels exceed the reported minimal inhibitory concentration (MIC) for Streptococcus pyogenes and Streptococcus pneumoniae. The average concentration of cefixime in saliva corresponded to its plasma free fraction (saliva/plasma [S/P] ratio; 0.34). However, this observation was not true for cephalexin, for which antibiotic concentrations in the saliva did not appear to correspond to its plasma free fraction (0.8-0.85), with an S/P ratio of only 0.092. Our findings indicate that an active transport mechanism exists for cefixime excretion into human oropharyngeal mucosa, whereas cephalexin is passively diffused, although to a limited extent, as measured by its salivary concentrations.