Quantitative and qualitative assessment of serum concentration monitoring and dosage adjustment of aminoglycosides

A prospective study was carried out in 50 adult patients to determine the extent and quality of aminoglycoside serum concentration monitoring and dosage adjustment in a U.K. teaching hospital. Data were collected concerning prescription details, assay results, and subsequent dosage adjustment, methods of dosage determination, and timing of samples. Thirty-three patients received aminoglycosides without a positive culture. The mean +/- SD initial doses were 1.75 +/- 0.45 mg/kg for gentamicin and 2.33 +/- 0.55 mg/kg for netilmicin. Doses were derived from physicians' personal experience for 35 patients and using nomograms for 11 patients. Prescribed and actual administration times were observed on 218 occasions. The difference between these times were significantly different (p less than 0.005). Fifty-six trough, 61 peak, and 61 random assays were carried out, of which 48% of troughs and 56% of peaks were in the therapeutic range. Dosage regimens were calculated based on actual serum concentration assay results using the Sawchuk-Zaske method. These calculated doses were compared to actual prescribed doses for each patient. The calculated doses were greater than 120% of the prescribed doses in 78% of patients. There was a significant tendency to underdose (p = 0.001). It is concluded that the service might benefit from an individualised approach to dosage determination.