FIGURE 11-6 (Continued)

B, Kidney cortical concentrations of gentamicin in rats given equal daily amounts of aminoglycoside in single injections, three injections, or by continuous infusion over 8 days. Each block represents the mean of seven rats ±SD. Significance is shown only between cortical levels achieved after continuous infusion and single injections (asterisk— P < 0.05; double asterisk—P < 0.01) [9].

In rats, nephrotoxicity of gentamicin is more pronounced when the total daily dose is administered by continuous infusion rather than as a single injection. Thus, a given daily drug does not produce the same degree of toxicity when it is given by different routes. Indeed, renal cortical uptake is "less efficient" at high serum concentration than at low ones. A single injection results in high peak serum levels that overcome the saturation limits of the renal uptake mechanism. The high plasma concentrations are followed by fast elimination and, finally, absence of the drug for a while. This contrasts with the continuous low serum levels obtained with more frequent dosing when the uptake at the level of the renal cortex is not only more efficient but remains available throughout the treatment period. Vm —maximum velocity.

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