**3.1 Antihypertensive drugs related with the citrus juice interactions**

In addition to increasing drug absorption with GFJ, citrus juices such as GFJ and orange juice can also prevent the intestinal absorption of drugs. For example, the intestinal absorption of fexofenadine, a third-generation antihistamine, is inhibited by GFJ, orange juice, and apple juice (Dresser, 2002). Furthermore, GFJ and orange juice also inhibit absorption of the ß-blocking agents, celiprolol (Lilja, 2003, 2004), atenolol (Lilja, 2005b), acebutolol (Lilja, 2005a), and talinolol (Schwarz, 2005).

#### **3.2 Mechanism of the citrus juice interactions**

It was reported that the citrus juice interactions are caused by inhibition of drugtransporting ability of intestinal organic anion transporting polypeptide (OATP) with contents in citrus juices. Fexofenadine is taken up by intestinal epithelial cells via OATP, which is expressed on the apical membrane, in the first step of absorption into general circulation from intestinal lumen (Dresser et al., 2002, 2005; Nozawa, 2004). Interestingly, GFJ enhances the intestinal absorption of talinolol in rats, putatively through inhibiting MDR1 activity and decreasing efflux from epithelial cells (Spahn-Langguth & Langguth, 2001). In humans, however, GFJ inhibits the intestinal absorption of talinolol (Schwarz et al., 2005). These observations suggest that in GFJ interactions with substrates of both of MDR1 and OATP, OATP uptake may dominate MDR1 efflux in humans but not in rodents.

#### **3.3 Citrus juice components involved in drug interactions**

Naringin, the major ingredient in GFJ, blocks the uptake of fexofenadine by the intestinal cells (Bailey, 2007). Hesperidin, a major component of orange juice, also inhibits intestinal absorption of celiprolol (Uesawa & Mohri, 2008a). Hesperidin is a flavonoid glycoside with

The component inhibitory potentials eliminated by the heat treatment of GFJ may be able to reflect the action *in vivo*. The results indicate that heat treatment could be useful in evaluating the potencies of GFJs in the drug interactions caused by furanocoumarins. It is believed that the *in vitro* evaluation systems using only untreated GFJ do not properly reflect the GFJ - drug interactions *in vivo* because these interactions are induced by furanocoumarin derivatives such as bergamottin and 6',7 '- dihydroxybergamottin in GFJ. Figure 17 and 18 show that order of each bland on the interaction potential estimated by FCI is not necessarily corresponding to the case estimated by only untreated GFJ. Therefore, we suggest that the inhibition potential of GFJ may be estimated by subtracting the microsomal CYP3A activity with HGJ from those activities obtained with the corresponding untreated GFJ. It is anticipated that the technical measurements of the GFJ-drug interaction potentials using FCI established in the present study, may be an effective method to identify the

**3. Citrus juice interactions related with the decrease of plasma drug** 

decreased. In this section, this type of interaction will be described.

acebutolol (Lilja, 2005a), and talinolol (Schwarz, 2005).

**3.3 Citrus juice components involved in drug interactions** 

**3.2 Mechanism of the citrus juice interactions** 

**3.1 Antihypertensive drugs related with the citrus juice interactions** 

Recently, citrus juices such as GFJ and orange juice can prevent the intestinal absorption of some β-blockers. As a result of this type of interactions, plasma concentrations of drugs are

In addition to increasing drug absorption with GFJ, citrus juices such as GFJ and orange juice can also prevent the intestinal absorption of drugs. For example, the intestinal absorption of fexofenadine, a third-generation antihistamine, is inhibited by GFJ, orange juice, and apple juice (Dresser, 2002). Furthermore, GFJ and orange juice also inhibit absorption of the ß-blocking agents, celiprolol (Lilja, 2003, 2004), atenolol (Lilja, 2005b),

It was reported that the citrus juice interactions are caused by inhibition of drugtransporting ability of intestinal organic anion transporting polypeptide (OATP) with contents in citrus juices. Fexofenadine is taken up by intestinal epithelial cells via OATP, which is expressed on the apical membrane, in the first step of absorption into general circulation from intestinal lumen (Dresser et al., 2002, 2005; Nozawa, 2004). Interestingly, GFJ enhances the intestinal absorption of talinolol in rats, putatively through inhibiting MDR1 activity and decreasing efflux from epithelial cells (Spahn-Langguth & Langguth, 2001). In humans, however, GFJ inhibits the intestinal absorption of talinolol (Schwarz et al., 2005). These observations suggest that in GFJ interactions with substrates of both of MDR1

and OATP, OATP uptake may dominate MDR1 efflux in humans but not in rodents.

Naringin, the major ingredient in GFJ, blocks the uptake of fexofenadine by the intestinal cells (Bailey, 2007). Hesperidin, a major component of orange juice, also inhibits intestinal absorption of celiprolol (Uesawa & Mohri, 2008a). Hesperidin is a flavonoid glycoside with

intensity of GFJ in the interactions.

**concentrations** 

a similar molecular structure to naringin. Hesperidin and naringin both inhibit the transport of OATP1A2 (Bailey et al., 2007), which mediates the intestinal uptake and systemic accessibility of ß-blockers, providing a mechanism for inhibiting absorption (Bailey et al., 2007).

In this section, our findings related with demonstration of a causal ingredient of the pharmacokinetic interaction between orange juice and celiprolol. It has been reported that the bioavailability of celiprolol is decreased by interaction with orange juice as well as GFJ because of inhibition of intestinal absorption of the drug (Lilja et al., 2004). We attempted to characterize this interaction by means of pharmacokinetic experiments with rats. Figure 19 shows pharmacokinetic profiles of plasma celiprolol levels when celiprolol with water (control), orange juice, and hesperidin solution were injected into the rat duodenum. However, under the abundant period of the elimination phase, especially for the orange juice group, the pharmacokinetic parameters were calculated in the period for descriptive purposes as well as other groups. AUC of celiprolol in the orange juice group was significantly decreased by 75.3 % compared with the control group. This observation corresponds with results in humans in which the AUC of celiprolol decreased by 83 %. It has been known in detail that when fexofenadine is taken with grapefruit or orange juice, both plasma concentration and AUC are decreased, as in the case of celiprolol. It has been reported that naringin, a major ingredient in GFJ, was the cause of the pharmacokinetic interaction between GFJ and fexofenadine (Bailey et al., 2007). Hesperidin, a major component of orange juice, is a flavonoid glycoside with an appearance and molecular structure similar to that of naringin. It has been demonstrated that hesperidin as well as naringin inhibit the transport of OATP1A2, an intestinal transporter related to the absorption of fexofenadine (Bailey et al., 2007). OATP1A2 probably facilitates the intestinal uptake and systemic accessibility of a broad battery of orally administered medications (Lee, 2005; Glaeser, 2007). Rat intestinal oatp3 is an orthologue of human OATP1A2 (Dresser et al., 2002). Although the mechanism of inhibition of celiprolol absorption by orange juice is unknown, flavonoids possibly contribute to the interaction because celiprolol undergoes inhibition with both orange juice and GFJ in the same way as fexofenadine. In fact, hesperidin as well as naringin affected significantly the uptake of fexofenadine by rat oatp3 (Dresser et al., 2002). We therefore designed our study with rats with the intention of identifying the role of hesperidin in orange juice in the interaction with celiprolol. As a result of the administration of celiprolol with hesperidin, significant decreases in AUC were observed compared with control, as also in the case of concomitant orange juice administration. On the other hand, the AUC in the hesperidin group was not significantly different from that in the orange juice group. These results demonstrate that hesperidin in orange juice contributes to the interaction observed. Inhibition of the celiprolol transporting pathway by hesperidin in the intestine is a possible mechanisms as is the case with fexofenadine - orange juice interaction. Furthermore, physicochemical effects such as binding and degradation of celiprolol with hesperidin might also contribute to the reduction in plasma concentrations due to decreased solubility and absolute amount of the drug in the intestinal duct. Initial decrementation of the celiprolol concentration in plasma by the coadministration of orange juice was greater than that due to hesperidin (Figure 19). In the rats receiving orange juice but not hesperidin, Tmax was also elongated significantly compared with controls. These observations suggest that a component or components of orange juice other than hesperidin may also contribute to variations in the absorption kinetics of celiprolol.

Pharmacokinetic Interactions of Antihypertensive Drugs with Citrus Juices 115

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Dose of celiprolol was 5 mg/kg body weight. Each point and vertical bar represents the mean and S.E., respectively (n=4 - 5). This figure was cited from the literature (Uesawa & Mohri, 2008a).

Fig. 19. Plasma concentration-time curves for celiprolol after it was administered into the duodenum of rats with water (control, white circle), orange juice (black circle) and 207.7 μg/mL hesperidin aqueous solution (black triangle).
