Impact of a Pharmacist-Initiated Therapeutic Drug Monitoring Consult Service for Children Treated with Gentamicin

Background: Starting in April 1988, the Pharmacy Department at The Hospital for Sick Children, Toronto, Ontario, provided a therapeutic drug monitoring (TDM) consult service for patients admitted to nursing units that did not have a clinical pharmacist as a member of the interdisciplinary team. This service was withdrawn on July 1, 2003. Objective: To determine the appropriateness of clinicians' response to exceptional serum concentrations of gentamicin (peak concentration outside the range 5 to 10 mg/L or trough concentration outside the range 0.6 to 2 mg/L) and subsequent laboratory monitoring before and after termination of the pharmacist-initiated TDM consult service. Methods: A chart review was conducted for the 6 months before and 6 months after removal of the pharmacist-initiated TDM consult service. All children admitted to general surgery units who received gentamicin therapy and who were reported to have exceptional serum concentrations of this drug were included. The ideal gentamicin dose assessment was determined for each concentration pair (peak and trough), and this ideal assessment was then compared with the dose assessment actually performed. Laboratory tests ordered (serum concentrations of gentamicin and creatinine) were compared with the institution's standard of care. Results: Clinicians' action in response to exceptional serum gentamicin concentrations was appropriate in 99% (93/94) of cases before removal of the consult service and in 64% (64/100) of cases after removal of the service (p < 0.001). Furthermore, there were statistically significant differences in subsequent gentamicin monitoring with respect to ordering of repeat gentamicin concentration after dose adjustment, timeliness of dose adjustment, and ordering and drawing of samples for weekly determination of trough gentamicin concentrations and serum creatinine for patients whose therapy lasted longer than 7 days. Conclusions: The appropriateness of assessment in cases of exceptional serum gentamicin concentration decreased significantly after withdrawal of a pharmacist-initiated TDM consult service.