A pharmacokinetic and tolerance study of Ro13-9904, a new cephalosporin antibiotic.

1 Six healthy male volunteers received a total of 2500 mg of a new cephalosporin antibiotic Ro13-9904 by intramuscular injection in five divided doses at intervals of 12 h. 2 No significant systemic side-effects were observed and this was confirmed haematologically and biochemically. 3 The drug was distributed following intramuscular injection reaching a mean peak plasma concentration of 55 micrograms ml-1 (range 46-66) 1 to 2 h after the first injection. 4 Monoexponential elimination of drug was demonstrated. No significant difference was recorded in the plasma half-life after the initial dose (mean 6.7 h) and at steady state (mean 6.7 h). The half-life is long compared with other cephalosporin antibiotics. 5 On the basis of the observed half-life, steady state should be reached within 48 h. A mean peak plasma concentration of 74 micrograms ml-1 (range 65-87) was recorded at steady state. Steady state plasma concentrations of Ro13-9904 with a dose of 500 mg every 13 h may be predicted from the pharmacokinetics of a single dose.