A radioreceptor assay for propranolol and 4-hydroxypropranolol

Area of Science:

• Pharmacology
• Analytical Chemistry

Background:

• Propranolol is a widely used beta-adrenergic blocker.
• Accurate measurement of propranolol and its active metabolite, 4-hydroxypropranolol, in plasma is crucial for therapeutic drug monitoring and pharmacokinetic studies.

Purpose of the Study:

• To describe a sensitive and reliable radioreceptor assay for quantifying propranolol and 4-hydroxypropranolol in plasma.
• To adapt the assay for measuring total beta-adrenergic blocking activity and the levels of free propranolol and 4-hydroxypropranolol.

Main Methods:

• Development and validation of a radioreceptor assay.
• Measurement of propranolol and 4-hydroxypropranolol concentrations in plasma.
• Assay modifications to determine total beta-adrenergic activity by stabilizing or oxidizing the metabolite.
• Quantification of free drug and metabolite levels.

Main Results:

• The assay demonstrated high sensitivity for propranolol (1.2 ng/ml) and 4-hydroxypropranolol (4.2 ng/ml).
• Inter- and intra-assay variations were below 10% for both compounds.
• The modified assay successfully differentiated total beta-adrenergic blocking activity from parent drug and metabolite contributions.
• More 4-hydroxypropranolol than propranolol was found to circulate in the free form.

Conclusions:

• The developed radioreceptor assay is feasible for measuring propranolol and 4-hydroxypropranolol in plasma.
• The assay can be adapted to determine total beta-adrenergic blocking activity and its components.
• This method allows for the measurement of free drug and metabolite levels, providing valuable pharmacokinetic insights.