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A sensitive radioligand binding assay for timolol in plasma.

¹Department of Clinical Pharmacology, University of Turku, Finland.

Journal of Pharmaceutical Sciences

|March 1, 1991

Summary

A new radioreceptor assay (RRA) accurately measures low picogram levels of timolol in plasma. This sensitive method offers superior detection limits compared to GC-MS, enabling effective drug monitoring.

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Area of Science:

Pharmacology
Analytical Chemistry
Biochemistry

Background:

Accurate quantification of beta-antagonists like timolol in biological fluids is crucial for therapeutic drug monitoring.
Existing analytical methods may lack the sensitivity or reproducibility required for low-dose drug analysis.

Purpose of the Study:

To develop and validate a sensitive and reproducible radioreceptor assay (RRA) for determining picogram levels of timolol in plasma.
To compare the performance of the RRA with established gas chromatography-mass spectrometry (GC-MS) techniques.

Main Methods:

Plasma sample preparation involving selective extraction or protein precipitation.
Radioligand binding assay using [3H](-)-CGP-12177 as the radioligand and rat reticulocyte membranes.
Quantification of timolol by competition with the radioligand for receptor binding sites.

Main Results:

The RRA demonstrated high recovery rates (≥90%) during sample preparation.
Achieved a detection limit of 30 pg/mL for timolol, exceeding GC-MS sensitivity by over 50-fold.
Excellent correlation (r = 0.99) between RRA and GC-MS results from clinical samples.
No interference observed from timolol metabolites.

Conclusions:

The developed RRA is a sensitive, reproducible, and accurate method for quantifying low picogram levels of timolol in plasma.
The RRA allows for monitoring of timolol concentrations after oral and ocular administration.
The assay methodology is adaptable for measuring other beta-antagonist drugs at picogram per milliliter concentrations.

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