Following a single intramuscular application of 1 g ceftizoxime, levels of the drug were determined in plasma as well as in suction blister fluid (SBF) and cantharides blister fluid (CBF). This regimen invariably led to both high and long-lasting plasma levels: 81 +/- 16 min post dose maximum plasma levels of 17.5 +/- 3.1 micrograms/ml were reached; 6 h post dose levels of 4.6 +/- 0.4 micrograms/ml were still found, i.e., 4375 and 1150 times, respectively, the MIC90% of Neisseria gonorrhoeae. The high plasma levels were parallelled by high concentrations in SBF, with peaks amounting to 8.4 +/- 1.0 micrograms/ml. Peak concentrations in CBF ranged from 8.1 to 15.7 micrograms/ml. Thus, the pharmacokinetic behavior of ceftizoxime given as a single intramuscular injection of 1 g explained the excellent clinical results of this regimen in uncomplicated gonorrhea.