Comparison of colistin-carbenicillin, colistin, and carbenicillin in Pseudomonas sepsis in monkeys.

Intravenous inoculation of 6.2 x 10(10) to 6.7 x 10(10)Pseudomonas aeruginosa organisms into rhesus monkeys 5 days after intratracheal inoculation of 2.0 to 2.5 mg of vincristine sulfate resulted in fatal sepsis in 8 of 10 untreated monkeys. When similarly infected monkeys were treated intramuscularly with 2.5 mg of colistin or 50 mg of carbenicillin per kg per day, all three monkeys in each treatment group survived; one of three monkeys receiving both antibiotics at the above doses died. Six of seven monkeys treated with 1.25 mg of colistin per kg per day and three of seven treated with 25 mg of carbenicillin per kg per day died; four of nine monkeys receiving both antibiotics at these doses died. A combination of the data obtained at both dose levels tested shows that 6 of 10, 3 of 10, and 5 of 12 monkeys, respectively, died after treatment with colistin, carbenicillin, and the colistin-carbenicillin combination. Antibacterial activity of serum from both infected and normal monkeys was not appreciably different when the two antibiotics were given singly or in combination. Under the conditions of this study and with the doses employed, the response of monkeys treated with the antibiotic combination did not differ significantly from that of monkeys treated with a single agent.