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Appl Environ Microbiol. 1969 March; 17(3): 457-461
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

In Vitro Antimicrobial Activity and Human Pharmacology of Cephalexin, a New Orally Absorbed Cephalosporin C Antibiotic

^a Department of Medicine, The New York Hospital-Cornell Medical Center, New York, New York 10021

ABSTRACT

Concentrations of cephalexin (an orally absorbed derivative of cephalosporin C) in serum and urine were determined in normal volunteers and patients. The in vitro antibacterial activity was also studied. All strains of group A ß-hemolytic streptococci and Diplococcus pneumoniae were inhibited by 3.1 µg/ml. Of the Staphylococcus aureus strains, 88% were inhibited by 6.3 µg/ml, and 12.5 µg/ml was inhibitory for all S. aureus, 80% of Escherichia coli, 72% of Klebsiella-Aerobacter, and 56% of Proteus mirabilis strains. About 90 to 96% of E. coli, Klebsiella Aerobacter, and P. mirabilis strains were inhibited by 25 µg of cephalexin per ml. Pseudomonas and indole-positive Proteus strains proved to be quite resistant to cephalexin. Cephalexin was well absorbed after oral administration. A peak serum concentration of cephalexin of at least 5 µg/ml was achieved in each volunteer with 250 and 500-mg doses. A mean peak serum concentration of 7.7 µg/ml was achieved with 250-mg doses; 12.3µg/ml was achieved with 500-mg doses of antibiotic. Food did not interfere with absorption. Probenecid enhanced both the peak serum concentration and the duration of antibiotic activity in the serum. Over 90% of the administered dose was excreted in the urine within 6 hr. The mean peak serum concentration of cephalexin after an oral dose of 500 mg was adequate to inhibit all group A streptococci, D. pneumoniae, and S. aureus, 85% of E. coli, and about 40 to 75% of Klebsiella-Aerobacter and P. mirabilis strains. Levels of cephalexin in urine were adequate to inhibit over 90% of E. coli, and P. mirabilis and 80 to 96% of Klebsiella-Aerobacter strains.

¹ Career Scientist of the Health Research Council of the City of New York (contract I-489).