Cost containment through therapeutic substitution of aminoglycosides

A therapeutic substitution policy (TSP) for tobramycin and gentamicin sulfate was implemented at the University of Texas Medical Branch (UTMB). The policy was designed by various physician-chaired hospital committees and clinical departments that collaborated with the pharmacy service. The goal was to encourage the medical house staff to use the most economical yet safe and effective aminoglycoside, without limiting the medical team's prerogative to select among alternatives within this antibiotic group. Cost data from the first 6 months of aminoglycoside use under the new policy projected an annual savings of $139,071 in drug expenditures and $242,472 in patient charges. Following the implementation of the TSP, a concurrent drug utilization review (DUR) was performed in 50 consecutive inpatients prescribed amikacin, tobramycin, or gentamicin sulfate. The objectives were to identify those aspects of prescribing and monitoring of aminoglycosides by house staff that could be improved by specific policy and/or education, and to evaluate those specific cases in which attending physician's approval allowed house staff to prescribe an aminoglycoside other than designated in the TSP. The audit revealed that house staff were compliant with 72% of the DUR criteria; however, at least one instance (mean of 5.04 +/- 2.21) of noncompliance occurred during the treatment of each patient. The most frequently encountered deficiencies were failure to monitor for ototoxicity, incorrect orders for at least one set of serum aminoglycoside concentrations, and improper dosage adjustments for those patients with renal insufficiency. In three cases, the attending physician approved house staff use of tobramycin instead of gentamicin sulfate for reasons of organism resistance, pre-existing renal impairment, and long-term treatment of osteomyelitis.