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Falsely elevated aminoglycoside serum levels in jaundiced patients
Drug Intelligence & Clinical Pharmacy
|July 1, 1983
Summary
Hyperbilirubinemia can cause falsely high aminoglycoside levels when using the Emit assay. Alternative testing methods are recommended for patients with elevated bilirubin levels to ensure accurate drug monitoring.
Area of Science:
- Clinical Chemistry
- Pharmacology
- Laboratory Medicine
Background:
- Accurate therapeutic drug monitoring is crucial for optimizing aminoglycoside efficacy and minimizing toxicity.
- The Emit assay is a common method for quantifying aminoglycoside concentrations in serum.
Observation:
- Two cases demonstrated significantly elevated aminoglycoside concentrations using the Emit assay in the presence of hyperbilirubinemia.
- Tobramycin levels were 26% higher with the Emit assay when total bilirubin was 20.1 mg/dL, compared to a microbiologic assay.
- Elevated Emit concentrations (34%) were also observed in another patient with a total bilirubin of 9.7 mg/dL.
Findings:
- Hyperbilirubinemia interferes with the Emit assay, leading to falsely increased aminoglycoside readings.
- Discrepancies between Emit and microbiologic assays diminished as bilirubin levels decreased below 4 mg/dL.
- Pharmacokinetic parameters and calculated dosage regimens varied substantially based on the assay method used.
Implications:
- Patients with total bilirubin levels exceeding 4 mg/dL may require alternative methods for aminoglycoside serum level determination.
- Clinical decisions based on Emit assay results in hyperbilirubinemic patients could lead to inappropriate dosing.
- This highlights the importance of considering potential interferences in immunoassays and validating results with orthogonal methods when necessary.