Gentamicin Level Trough

1. Pharmokinetic factors including dosage form, mode of administration, and concomitant drug therapy can influence appropriate time of specimen collection following administration of gentamicin.

2. For patient’s receiving gentamicin via conventional dosing methods peak and trough drug monitoring should begin after a steady-state is achieved (usually 3-4 doses).

A. Specimen for peak concentration should be drawn 60-90 minutes after intravenous infusion.

B. Specimen for trough concentration should be drawn within 30 minutes of next dose.

3. For patient’s receiving gentamicin via a pulse-dosing method, monitoring can begin after first dose, because steady-state conditions are not obtained. Monitoring strategies will vary with dosing regimens. When using pulse dosing nomograms, a timed specimen should be drawn 8 to 12 hours after completion of drug infusion in order to determine subsequent dosing interval. This should be repeated at 3 to 7 day intervals or more frequently as warranted.

4. Concentration of beta-lactam antibiotics (penicillin and cephalosporin) at therapeutic levels may inactivate gentamicin in vivo and in vitro. Specimen from patient’s receiving beta-lactam antibiotics must be analyzed immediately upon receipt or stored to prevent in vitro inactivation of gentamicin.