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Collaboration between pharmacy and laboratory: defining total allowable error limits for therapeutically monitored
K M Radomski1, B A Bush, M H Ensom
1College of Pharmacy, University of Kentucky, Lexington, USA.
The Annals of Pharmacotherapy
|March 13, 1998
Summary
Therapeutic drug monitoring (TDM) assay variability often exceeds clinically tolerated error for aminoglycosides like amikacin, gentamicin, and tobramycin, impacting their clinical utility.
Area of Science:
- Clinical Chemistry
- Pharmacology
- Laboratory Medicine
Background:
- Therapeutic drug monitoring (TDM) relies on accurate drug concentration measurements.
- Assay variability must be understood in relation to clinically acceptable error margins.
Purpose of the Study:
- To determine the total allowable error (TEa) for common drug assays.
- To compare laboratory performance with clinically defined variability limits.
Main Methods:
- Monthly coefficient of variation (CV) was recorded for 13 drug assays at therapeutic range limits.
- Dosing simulations estimated serum concentrations after practical dosage adjustments.
- Calculated TEa was compared against the laboratory's CV.
Main Results:
- Laboratory CV exceeded TEa for amikacin, gentamicin, and tobramycin at trough levels.
- Simulations in renal impairment and obesity showed TEa less than CV for amikacin.
- Assay variability for these aminoglycosides surpassed expected concentration changes from dosage adjustments.
Conclusions:
- Assay variability for certain aminoglycosides exceeds clinically tolerated error.
- Understanding assay variability relative to TEa is crucial for assessing TDM's clinical usefulness.