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Updated: Aug 7, 2026

A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
Major determinant factors of the extent of interaction between grapefruit juice and calcium channel antagonists
Ayako Ohnishi1, Hisakazu Ohtani, Yasufumi Sawada
1Biostatistics Department, Shionohi and Co., Ltd, Osaka, Japan.
Aim:
To evaluate quantitatively the influence of bioavailability and plasma unbound fraction (f(u)) on the extent of interaction between grapefruit juice (GFJ) and calcium antagonists.
Methods:
The extent of drug-GFJ interaction was evaluated from reported clinical interaction studies of 11 calcium antagonists. The relationship between extent of interaction and bioavailability or f(u) was analysed.
Results:
The following significant hyperbolic relationships were observed: [Extent] = 12.2/[bioavailability] + 1 and [Extent] = 0.718/[f(u)] + 1.
Conclusions:
Bioavailability and f(u) are major determinant factors of calcium antagonist-GFJ interaction: a drug with smaller bioavailability or lower f(u) is likely to exhibit a more potent interaction, and vice versa.
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