In six healthy volunteers receiving constant intravenous infusions of cefazolin sodium, a steady state was reached during the third hour, with serum concentrations four times as high as those obtained with cephalothin sodium. Single intramuscular injections gave average peak blood levels more than twice as high as with cephaloridine. Serum half-life was 1.8 hours for cefazolin, compared with 1.12 hours for cephaloridine and 0.47 hour for cephalothin. Lower renal clearance of cefazolin, as compared to that of cephaloridine and cephalothin, was mainly responsible for its higher and more prolonged blood levels. Serum protein binding was 86% for cefazolin, compared to 65% for cephalothin and 20% for cephaloridine; this was associated with a smaller apparent volume of distribution. Almost all of the cefazolin administered was recovered in the urine within 24 hours, and no metabolic breakdown product was detectable.
Regamey C, Gordon RC, Kirby WMM. Cefazolin vs Cephalothin and Cephaloridine: A Comparison of Their Clinical Pharmacology. Arch Intern Med. 1974;133(3):407–410. doi:10.1001/archinte.1974.00320150081009
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