Ticarcillin vs carbenicillin: clinical pharmacokinetics.

The pharmacokinetic characteristics of ticarcillin, a semisynthetic penicillin more active than carbenicillin against Pseudomonas, were compared to those of carbenicillin in 12 healthy volunteers. Following an intravenous infusion of 2 gm in 5 min, there was a lower average serum level for ticarcillin (218 mug/ml) than for carbenicillin (301 mug/ml), but after 2 hr the differences were not significant. The biologic half-life of ticarcillin was slightly longer than that of carbenicillin (72 and 65 min, P smaller than 0.01) and its volume of distribution was larger (15.7 and 12.3 l, P smaller than 0.01). Eighty-six per cent of the dose of ticarcillin and 99 percent of the dose of carbenicillin was recovered in the urine in 24 hr. Similar but much less marked blood level differences were noted with 2 gm, 30-min infusions. An intravenous infusion of 1 gm/hr gave average steady-state blood levels of about 124 mug/ml for both antibiotics. Probenecid, administered 1 hr before the infusion, caused significant and similar increases in blood levels, half-lives, and volumes of distribution of the 2 antibiotics. Protein binding in 100 percent human serum was 50 percent and 65 percent for carbenicillin and ticarcillin, respectively. These relatively small but definite differences in the pharmacokinetics of ticarcillin and carbenicillin are not likely to be of clinical significance.