Gentamicin serum concentration monitoring

Gram-negative coverage is indicated for patients with diabetes, HIV infection, prosthetic valves, or those receiving immunosuppressive agents (gentamicin 2 mg/kg intravenously with serum concentration monitoring). 

The aminoglycosides (i.e., amikacin, gentamicin, and tobramycin) and vancomycin remain the most common agents for which serum concentrations are monitored. A summary of the recommendations for serum concentration monitoring of these agents is shown in Table 103-2. 

Gentamicin is an aminoglycoside. All aminoglycosides tend to be nephrotoxic and ototoxic. The dose must be reduced and serum concentrations must be monitored in patients with impaired renal function. Concomitant administration of aminoglycosides and other nephrotoxic drugs, such as certain diuretics, ciclosporin, teicoplanin and vancomycin should be avoided. 

Gentamicin-induced magnesium depletion is most likely to occur in older patients when large doses are used over long periods of time (16). Under these circumstances, serum concentrations and urinary electrolyte losses should be monitored. 

Fig. 1.12 Serum concentration-time profile of gentamicin in an animal after intravenous administration, illustrating three phases of disposition. Alpha and beta phases, relevant for therapeutic monitoring, are the only phases evident when drug concentrations are monitored over a short time after dosing (inset). When a sensitive assay is employed to monitor drug concentrations for prolonged periods, the third (gamma) phase becomes evident. It is this last phase that is responsible for predicting tissue withdrawal times. (Reproduced with permission from Riviere (1988).)...

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