Pharmacokinetic interaction of aztreonam with other antibiotics

The pharmacokinetic interaction of the monobactam antibiotic aztreonam with cephradine, clindamycin, gentamicin, metronidazole, and nafcillin was investigated in five separate studies in 48 healthy male volunteers. All drugs were administered by 30-minute intravenous infusions in single-dose, three-way balanced cross-over studies. Drug levels were measured in serum, protein-free filtrate of serum, and urine. Small changes of no clinical significance were seen when aztreonam was given simultaneously with another antibiotic as compared with each drug alone. Maximum serum concentrations of aztreonam were reduced by 12.6 and 9.8 per cent when it was given with gentamicin and metronidazole, respectively. The percentage of serum aztreonam bound to protein fell by a maximum of 5.0 per cent when the monobactam was given in conjunction with nafcillin and rose by 5.1 per cent when accompanied by cephradine. Twenty-four-hour cumulative urinary excretion of aztreonam and clindamycin rose by 5.2 and 10.9 per cent, respectively, when they were administered simultaneously.