Therapy of staphylococcal infections in monkeys. VII. Comparison of cyclacillin and nafcillin.

Intravenous inoculation of a penicillin-resistant phage type 80/81 staphylococcus caused lethal infection in seven of eight untreated monkeys. Daily intragastric administration of 50 mg/kg given in two equal morning and afternoon doses of cyclacillin and nafcillin was followed by mortalities of four of four and two of four monkeys, respectively. After 100 mg per kg per day, three of four and one of four monkeys receiving cyclacillin and nafcillin, respectively, died. Thus, mortality in controls and cyclacillin-treated monkeys was seven of eight as compared to three of eight after nafcillin treatment. Although the staphylococcus was more resistant to cyclacillin (minimal inhibitory concentration = 7.80 mug/ml) than to nafcillin (minimal inhibitory concentration = 0.31 mug/ml), regular rapid absorption and high levels of the former suggested potential efficacy. However, the similar mortality in cyclacillin-treated and control monkeys indicated that the in vitro data did not, in this instance, conform to the in vivo observations.