Background and objectives: Short-term fasting differentially alters cytochrome P450 (CYP) mediated drug metabolism. This has been established by using CYP-enzyme selective probe drugs. However, the observed effects of fasting on the pharmacokinetics of these probe drugs may also include the effects of altered plasma protein binding of these drugs. Therefore, we studied the effect of short-term fasting on protein binding of five commonly used probe drugs [caffeine (CYP1A2), metoprolol (CYP2D6), midazolam (CYP3A4), omeprazole (CYP2C19) and S-warfarin (CYP2C9)].
Methods: The free and total plasma concentrations of the five probe drugs were analyzed by LC-MS/MS in samples retrieved in a cross-over study in which nine healthy subjects received an intravenous administration of the cocktail after an overnight fast (control) and after 36 h of fasting.
Results: Short-term fasting increased plasma free fatty acid concentrations from 0.48 mmol/L (control) to 1.29 mmol/L (36 h fasting) (p = 0.012). Short-term fasting did not alter the free fractions of caffeine, metoprolol and omeprazole compared to the control intervention (p > 0.05). Power to detect a difference for midazolam and S-warfarin was low since the majority of free concentrations were below the limit of quantification.
Conclusions: This study demonstrates that short-term fasting does not alter protein binding of the probe drugs caffeine, metoprolol and omeprazole.