Ayuko Imaoka

Prediction of the extent and variation of grapefruit juice-drug interactions from the pharmacokinetic profile in the absence of grapefruit juice

The aim of this study was to develop a method for predicting the extent of grapefruit juice (GFJ)–drug interactions and their interindividual variations from the pharmacokinetic profile in the absence of GFJ. The pharmacokinetic profiles of 13 drugs after intravenous and oral administration were used to develop and validate the method. For each drug, the proportion absorbed into the intestine and the intestinal availability (Fg) were calculated from clinical data taken from the literature. Then, the AUC ratio (the ratio of the AUC with GFJ to that without GFJ) was predicted by assuming that Fg was 1.0 when GFJ was concomitantly ingested. According to the developed method, the AUC ratio of felodipine was 2.50 and its coefficient of variation (CV) was 45%, which agreed well with the observed AUC ratio of 2.48 and CV of 51%. Although the developed method overestimated the AUC ratios of some drugs such as nisoldipine, no underestimation occurred. The predicted CV values were consistent with those observed. The developed method might be useful to predict the AUC ratio, along with its interindividual variation, from the pharmacokinetic profile in the absence of grapefruit juice. Copyright

5-Fluorouracil treatment alters the expression of intestinal transporters in rats

5‐Fluorouracil (5‐FU), an anticancer drug, causes severe gastrointestinal damage, which may affect the absorption of orally administered drugs including the substrates of intestinal uptake and efflux transporters. This study aimed to investigate quantitatively the effect of 5‐FU‐induced intestinal damage on the expression of intestinal transporters: P‐glycoprotein (P‐gp), breast cancer resistance protein (BCRP) and peptide transporter 1 (PEPT1) in rats. The rats were treated with 5‐FU (30 mg/kg/day, p.o.) for 5 days to induce intestinal damage, and then the upper, middle and lower intestinal segments were removed. The mRNA and protein expression levels of these transporters in each segment were determined using quantitative real‐time PCR and Western blotting, respectively. In the 5‐FU‐treated rats, the protein levels of P‐gp and Bcrp in the upper segment were significantly increased to 15‐ and 2.6‐fold of the control, respectively, while those in other segments were unaffected. Pept1 expression was increased by 5‐FU in almost all segments. A remarkable increase in P‐gp expression was shown, the uptake of digoxin, a P‐gp substrate, in each intestinal segment was measured using a rat everted sac. As a result, the uptake of digoxin in the upper segments of 5‐FU‐treated rats was decreased compared with that of the control. In conclusion, 5‐FU‐induced intestinal damage was shown to alter the expression of these transporters, especially in the upper intestinal segment, while the characteristics of the influence varied among the transporters. The 5‐FU‐induced intestinal damage may affect transporter‐mediated drug absorption of orally administered drugs in the clinical setting.

Inactivation kinetics and residual activity of CYP3A4 after treatment with erythromycin

This study aimed to characterize the inactivation kinetics of cytochrome P450 3A4 (CYP3A4) by erythromycin, which involves mechanism‐based inhibition (MBI), in detail. In addition to an MBI assay based on the conventional method in which erythromycin and recombinant CYP3A4 were pre‐incubated for 15 min, the study also evaluated the long‐term MBI kinetics of this reaction by pre‐incubation for 120 min. Mechanism‐based inhibition profiles were obtained using three typical substrates, testosterone, midazolam and nifedipine. In the long‐term assay, erythromycin evoked a time‐dependent biphasic reduction in enzyme activity, but some residual activity (α) was detected in the terminal phase. The inactivation rate constant obtained in the presence of 30 μm erythromycin using nifedipine as a substrate was 1.44‐fold higher than that acquired using testosterone, while there was no difference among the α values obtained with the three substrates. In the short‐term assay, time‐dependent monophasic inactivation was observed. To extrapolate these data to in vivo, the extent of the increase in the area under the curve (AUC ratio) induced by erythromycin was estimated from the results of the conventional short‐term experiment and the long‐term experiment examining residual activity. The AUC ratio estimated from the long‐term kinetics (2.92) was closer to the clinically reported values (3.3–4.42). In conclusion, the relatively long‐term evaluation of the kinetics of CYP3A4 inactivation revealed that the enzyme was not fully inactivated by erythromycin. To improve the estimation of the extent of the drug–drug interactions induced by MBI from in vitro data, longer‐term investigations of the target enzymes inactivation profile might be necessary.

In silico evaluation of warfarin–bucolome therapy

Purpose: Some reports have suggested that bucolome, an inhibitor of cytochrome P450 2C9, is useful for decreasing inter‐patient variation in warfarin clearance. The purpose of the present study was to evaluate the utility of the concomitant administration of bucolome and warfarin using an in silico approach. Methods: In vitro data regarding the enzymatic kinetics of (S)‐warfarin and bucolome were collected from the literature. As a validation study, the geometric mean (GM) of the oral unbound clearance of (S)‐warfarin and its inter‐patient variation (assessed using the standard deviation of its natural logarithm (σ)) were predicted using a physiologically based population pharmacokinetic simulator (SimcypTM) and compared with clinical data. The utility of the concomitant administration was evaluated by comparing the GM and σ values predicted under various conditions (the prediction study). Results and Discussion: The σ values in the presence and absence of bucolome were predicted to be 0.73 and 0.68, respectively, suggesting that bucolome might increase the inter‐patient variation, as clinically observed. In the prediction study, the σ value of the bucolome co‐administered group was greater in almost all of the examined conditions. In conclusion, the concomitant administration of bucolome might not be useful for reducing the inter‐patient variation of (S)‐warfarin pharmacokinetics. Copyright