Falsely elevated aminoglycoside serum levels in jaundiced patients

Two cases in which hyperbilirubinemia produced falsely elevated aminoglycoside concentrations, using the Emit assay, are described. Patients' sera were analyzed by both the Emit and a microbiologic assay. The first patient had a 26-percent greater tobramycin concentration with the Emit assay, as compared with the microbiologic assay, when the total bilirubin was 20.1 mg%. For the same patient, there was essentially no difference between the two assays when the total bilirubin was 4 mg%. The Emit concentrations in the other patient were 34-percent elevated with a total bilirubin of 9.7 mg%. Pharmacokinetic analysis also was performed on serum levels reported by each method. Calculated kinetic parameters and dosage regimens varied greatly. Patients with total bilirubin concentrations greater than 4 mg% may need to have aminoglycoside serum levels assayed by a method other than the Emit assay.