The blood levels and renal clearance in rabbits and man of an antibiotic derived from B. subtilis (bacitracin).

The renal clearances of penicillins F, G, and X have been shown to approximate the total renal plasma flow (1, 2), varying between 529 and 865 ml. per minute in man, and 23 to 111 ml. per minute in rabbits (2). In consequence of that rapid excretion, the serum concentration of penicillin G decreases after its intramuscular injection in aqueous solution, at an average rate of 2 to 3 per cent of the residual penicillin per minute, and 70 to 80 per cent per hour; and it disappears from the blood even more rapidly after intravenous injection (3, 8). A therapeutic agent equal to penicillin in bactericidal activity, but with a slower rate of absorption or excretion, would provide effective levels for longer periods of time, and might be correspondingly more effective than penicillin similarly injected. The antibiotic agent discovered, by Johnson, Anker and Meleney (4) in culture filtrates of a strain of B. subtilis (Tracy), and termed by them bacitracin, possesses some of these properties. As will be here shown, it is excreted by both rabbits and man at a rate which corresponds approximately to the rate of glomerular filtration, rather than to the total renal plasma flow. In consequence, the blood levels observed after its intravenous or intramuscular injection fall off more slowly than do those of penicillin, and a given dosage provides effective levels for longer periods. The implications of these findings with respect to the therapeutic efficacy of this agent are discussed in the text.