Effects of grapefruit juice on pharmacokinetics of atorvastatin and pravastatin in Japanese

Abstract

Aims

To investigate the effects of repeated grapefruit juice (GFJ) intake on the pharmacokinetics of atorvastatin and pravastatin in Japanese subjects.

Methods

Two randomized, two-way crossover studies were performed. GFJ or water was given to two groups of 10 subjects each three times daily for 2 days. On the third day, single 10 mg doses of atorvastatin or pravastatin were orally administered with GFJ or water, and an additional 250 ml of GFJ or water was taken before lunch and dinner. Plasma concentrations of atorvastatin and its metabolites were determined over 48 h postdosing and of pravastatin and its metabolites over 24 h postdosing.

Results

Compared with in the water group, the AUC(0,48 h) of atorvastatin acid significantly increased by 1.40 fold (95% CI 1.02, 1.92; P < 0.05) when atorvastatin was taken with GFJ. AUC(0,48 h) and C_max of atorvastatin lactone significantly increased by 1.56 (95% CI 1.33, 1.83; P < 0.001) and 1.29 fold (95% CI 1.09, 1.51; P < 0.01), respectively, when atorvastatin was taken with GFJ. No significant changes were detected in any pravastatin pharmacokinetic parameter examined when pravastatin was taken with GFJ. However, AUC(0,24 h) of pravastatin lactone increased 1.31 fold (95% CI 1.01, 1.71; P < 0.05) with GFJ intake.

Conclusions

GFJ was confirmed to significantly affect the pharmacokinetics of atorvastatin but had little or no effect on those of pravastatin in Japanese subjects.

Introduction

Multidrug therapy is common in the clinical setting. Yet along with the possibility of better therapeutic effects provided by combination drugs, problems caused by drug–drug interactions often arise. Following oral administration, drugs are normally absorbed through the GI tract into the portal veins, and enter into the circulating bloodstream after passing through the liver. During this process, some drugs are metabolized to some extent by enzymes such as cytochrome P-450 (CYP) complex enzymes in the liver, and by CYP3A4 in particular in the epithelial cells of the small intestine.

Grapefruit juice (GFJ) contains various furanocoumarin derivatives [1–3] that inhibit CYP3A4 located in the GI tract walls [4]. Concomitant use of GFJ is known to increase plasma concentrations of some dihydropyridine calcium antagonists, anti-allergic agents, immunosuppressive agents, and anti-HIV agents [5, 6]. In addition, GFJ inhibits P-glycoprotein efflux transporters located in the GI tract mucosa, thus enhancing uptake of P-glycoprotein substrate drugs from the intestinal tract [7]. Hence since GFJ is a commonly used beverage, it is of interest to investigate interactions between GFJ and various prescription drugs that are likely to be affected.

Hypercholesterolaemia is a major risk factor for ischaemic heart disease [8]. To decrease concentrations of cholesterol in the blood, three strategies have been considered: suppression of its absorption; inhibition of its biosynthesis; and promotion of its excretion. HMG-CoA reductase inhibitors reduce blood cholesterol concentrations by competitive inhibition of HMG-CoA reductase, a rate-limiting factor in cholesterol biosynthesis. Most of the HMG-CoA reductase inhibitors are metabolized by CYP3A4, and they may possibly interact with other drugs that act at CYP3A4 when taken concomitantly. However, since pravastatin is not metabolized by CYP3A4, there is a low possibility that it enters into such drug–drug interactions. Thus in this respect, pravastatin is considered safer than the other HMG-CoA reductase inhibitors [9, 10].

The effects of GFJ intake on the pharmacokinetic disposition of simvastatin, lovastatin, atorvastatin, and pravastatin have already been examined [11–13]. Plasma concentrations of simvastatin, lovastatin, and atorvastatin, which are all metabolized by CYP3A4, are significantly increased when these drugs are taken with GFJ, whereas those of pravastatin are not affected by GFJ intake. However, no studies have been conducted in Japanese subjects to date. In addition to ethnic differences between the subjects investigated in the previous studies and Japanese subjects, the normally used daily doses of HMG-CoA reductase inhibitors differ from those in European and US populations (10 mg vs 40 mg, respectively). Hence we performed two randomized, two-way crossover studies to investigate the effects of repeated GFJ intake on the pharmacokinetics of pravastatin and its lactone, to which it undergoes partial biotransformation in vivo[13], and of atorvastatin, atorvastatin lactone, and the CYP3A4-mediated conversion products 2-hydroxyatorvastatin acid and 2-hydroxyatorvastatin lactone [13, 14], respectively, in Japanese subjects using a common brand of GFJ marketed in Japan.

Methods

Subjects

Twenty healthy male adult volunteers were randomized into two study groups of 10 subjects each. In study I (age 20–33 years; weight 55.0–71.0 kg; BMI 19.8–24.7) atorvastatin was administered to all 10 subjects, and in study II (age 21–33 years; weight 50.8–76.9 kg; BMI 18.6–24.9) pravastatin was administered to all 10 subjects. Written informed consent was obtained from all subjects prior to participation.

All subjects underwent past medical history interviews and physical and laboratory examinations (haematology, serum biochemistry, and urinalysis) to confirm that they were healthy. Smokers were not included, nor were subjects deemed alcohol or drug dependent. Other exclusion criteria included having participated in a clinical study during the past 4 months, having had drawn >200 ml of blood in the past 3 months, and taking grapefruit, GFJ, St John's Wort, or any other drugs within 2 weeks prior to the study.

This study was conducted between July 10, 2001 and September 13, 2001 at the Medical Corporation Keiyu-Kai-Group, Obara Hospital, Tokyo, Japan, in compliance with the GCP and other related statutes. Approval was obtained from the clinical study review board of the medical institution in which the study was conducted.

Study design

Two randomized two-phase open crossover studies were conducted each in 10 subjects. The drug washout period was 3 weeks. For 2 days prior to the study-drug administration, 250 ml of either 100% GFJ from concentrate (Tropicana Homemade Style, Kirin Beverage Corp., Tokyo, Japan) or water was given to half of the subjects in each group three times daily (09.00 h, 13.00 h, 18.00 h). On the day of the study drug administration, the subjects were fasted overnight, and a single dose (10 mg) of either atorvastatin (Lipitor® 10 mg tablet, Yamanouchi Pharmaceutical Co, Ltd, Tokyo, Japan; study I) or pravastatin (Mevalotin® 10 mg tablet, Sankyo Co, Ltd, Tokyo, Japan; study II) was orally administered with 250 ml of either GFJ or water at 09.00 h. On the same day, 250 ml of either GFJ or water was taken at 13.00 h and 18.00 h. Both studies were then repeated substituting GFJ for water in those who had been taking water and vice versa; hence each subject acted as his own control.

Blood sample collection

Venous blood (10 ml) was collected from the brachial vein of each subject at each blood sampling time. In study I, in both phases, blood was collected immediately before and at 0.5, 1, 2, 3, 4, 6, 8, 12, 24, 36, and 48 h after administration of atorvastatin. In study II, blood was collected immediately before and at 0.5, 1, 2, 3, 4, 6, 8, 12, and 24 h after administration of pravastatin. Blood samples were centrifuged for 10 min at 4 °C and 3000 rev min⁻¹, promptly after collection and the separated plasma was frozen at −20 °C until use.

Drug concentrations

Concentrations of atorvastatin acid, atorvastatin lactone, 2-hydroxyatorvastatin acid, 2-hydroxyatorvastatin lactone, pravastatin, and pravastatin lactone in plasma were determined by liquid chromatography-mass spectrometry (LC/MS/MS) at MDS Pharma Services Inc (Montreal, Canada). The quantification limit was 0.2 ng ml⁻¹ for all substances determined. The interassay coefficient of variation (CV) was less than 15% for all analytes at relevant concentrations. AUC(0,48 h), AUC(0,24 h), AUC(0,∞), C_max, t_max, mean residence time (), and t_1/2 were calculated from the plasma concentrations using a commercially available software package (WinNonlin®, Ver. 3.1; Pharsight, Inc, Mountain, CA). In addition, CL/F was calculated for atorvastatin acid and pravastatin only.

Statistical analysis

Geometric means and their 95% confidence intervals were calculated for AUC(0,48 h), AUC(0,24 h), AUC(0, ∞) and C_max. For the other pharmacokinetic parameters, arithmetic means and their 95% confidence intervals were calculated. Analysis of variance proper for the crossover study was conducted for each of the pharmacokinetic parameters (log [AUC(0,48 h)], log [AUC(0,24 h)], log [AUC(0, ∞)], log [C_max], t_max, CL/F, and t_1/2) to calculate the 95% confidence intervals and to detect differences between the administration groups. Furthermore, the 95% confidence intervals for the mean value of the GFJ and water intake ratios were calculated from exponential conversions of AUC(0,48 h) and C_max in study I and AUC(0,24 h) and C_max in study II.

Results

Study I

Average AUC(0,48 h) and AUC(0, ∞) of atorvastatin acid in plasma increased 1.40 fold (95% CI 1.02, 1.92; P < 0.05) and 1.33 fold (95% CI 1.06, 1.68; P < 0.05), respectively, when GFJ was taken together with atorvastatin. Average CL/F decreased by 117 l h⁻¹ (95% CI 27, 206; P < 0.05). However, no significant changes were detected in C_max, t_max, , or t_1/2(Figure 1, Tables 1 and 2).

Figure 1.

Plasma concentrations (mean ± SD) of atorvastatin acid (above) and atorvastatin lactone (below) after a single 10 mg dose of atorvastatin. Water intake group (○); GFJ intake group (•)

Table 1.

AUC(0,48 h), AUC(0,24 h), AUC(0, ∞) and C_max

(a)	Atorvastatin acid			Atorvastatin lactone
	Water	GFJ	Ratio	Water	GFJ	Ratio
AUC(0,48 h)	19.0	26.6	1.40*	10.5	16.3	1.56‡
(ng ml−1 h)	(12.6, 28.6)	(18.1, 39.0)	(1.02, 1.92)	(5.7, 19.2)	(8.4, 31.5)	(1.33, 1.83)
AUC(0, ∞)	24.5	32.6	1.33*	20.1	32.0	1.63‡
(ng ml−1 h)	(17.7, 33.8)	(24.0, 44.2)	(1.06, 1.68)	(12.4, 32.4)	(20.5, 49.9)	(1.40, 1.89)
Cmax	4.6	3.6	0.80	0.8	1.0	1.29†
(ng ml−1)	(3.2, 6.6)	(2.5, 5.3)	(0.47, 1.34)	(0.5, 1.3)	(0.7, 1.7)	(1.09, 1.51)

(b)	2-Hydroxyatorvastatin acid			2-Hydroxyatorvastatin lactone
	Water	GFJ	Ratio	Water	GFJ	Ratio
AUC(0,48 h)	17.4	6.0	0.34*	29.2	23.3	0.80*
(ng ml–1 h)	(11.7, 25.8)	(2.0, 18.3)	(0.15, 0.81)	(20.5, 41.7)	(15.3, 35.5)	(0.67, 0.95)
AUC(0, ∞)	26.7	20.9	0.79	35.6	32.9	0.91
(ng ml−1 h)	(20.4, 34.9)	(14.6, 30.0)	(0.63, 1.00)	(25.4, 50.1)	(23.0, 47.1)	(0.82, 1.02)
Cmax	1.5	0.5	0.34†	1.6	1.1	0.67‡
(ng ml−1)	(1.1, 2.1)	(0.3, 0.8)	(0.21, 0.56)	(1.1, 2.4)	(0.7, 1.6)	(0.56, 0.80)

(c)	Pravastatin			Pravastatin lactone
	Water	GFJ	Ratio	Water	GFJ	Ratio
AUC(0,24 h)	37.2	37.1	1.00	1.7	2.3	1.31*
(ng ml−1 h)	(25.7, 53.9)	(29.3, 46.8)	(0.74, 1.34)	(1.4, 2.2)	(1.7, 2.9)	(1.01, 1.71)
AUC(0, ∞)	40.0	39.9	1.00	2.4	3.1	1.25
(ng ml−1 h)	(28.1, 57.0)	(31.4, 50.5)	(0.73, 1.35)	(2.0, 3.0)	(2.5, 3.8)	(0.92, 1.69)
Cmax	13.3	11.6	0.88	0.8	1.0	1.28
(ng ml−1)	(8.2, 21.3)	(9.3, 14.5)	(0.62, 1.24)	(0.6, 1.0)	(0.8, 1.1)	(0.95, 1.73)

AUC(0,48 h), AUC(0,24 h), AUC(0, ∞) and C_max values indicate geometric means. Ratio indicates ratio of GFJ to water values. Values in parentheses represent 95% confidence intervals.

^*P < 0.05;

^†P < 0.01;

^‡P < 0.001.

Table 2.

t_max, , t_1/2, and CL/F

(a)	Atorvastatin acid			Atorvastatin lactone
	Water	GFJ	GFJ-water	Water	GFJ	GFJ-water
tmax (h)	0.7	1.3	0.5	5.5	6.2	0.7
	(0.5, 0.9)	(0.7, 1.8)	(−0.2, 1.3)	(3.3, 7.7)	(4.3, 8.0)	(−2.5, 3.8)
(h)	12.1	14.4	2.3	15.2	19.3	4.2*
	(9.6, 14.6)	(12.8, 16.1)	(−0.3, 5.0)	(12.6, 17.8)	(15.2, 23.3)	(1.2, 7.2)
t1/2 (h)	9.7	10.6	0.9	9.4	12.3	3.0*
	(7.7, 11.7)	(9.4, 11.7)	(−1.7, 3.4)	(7.6, 11.1)	(9.5, 15.1)	(1.1, 5.0)
CL/F	446	329	−117*
(l h−1)	(309, 583)	(245, 413)	(−206, −27)

(b)	2-Hydroxyatorvastatin acid			2-Hydroxyatorvastatin lactone
	Water	GFJ	GFJ-water	Water	GFJ	GFJ-water
tmax (h)	1.9	12.0	10.1‡	7.2	11.2	4.0†
	(0.9, 2.9)	(12.0, 12.0)	(9.1, 11.1)	(5.1, 9.4)	(10.0, 12.4)	(1.8, 6.2)
(h)	16.0	29.9	14.0†	17.0	29.5	12.3‡
	(13.1, 18.9)	(23.6, 36.2)	(8.3, 19.7)	(14.8, 19.2)	(23.0, 35.9)	(7.1, 17.5)
t1/2 (h)	10.8	17.6	6.9*	10.5	16.9	6.3†
	(9.3, 12.3)	(12.7, 22.4)	(2.1, 11.8)	(9.0, 11.9)	(12.9, 20.8)	(3.0, 9.6)

(c)	Pravastatin			Pravastatin lactone
	Water	GFJ	GFJ-water	Water	GFJ	GFJ-water
tmax (h)	1.2	1.4	0.2	1.4	1.9	0.4*
	(0.9, 1.5)	(1.0, 1.8)	(−0.3, 0.7)	(1.0, 1.8)	(1.6, 2.1)	(0.0, 0.8)
(h)	4.1	4.2	0.2	3.1	3.1	0.0
	(3.4, 4.7)	(3.5, 4.9)	(−0.7, 1.0)	(2.8, 3.5)	(2.7, 3.5)	(−0.4, 0.4)
t1/2 (h)	3.0	3.0	0.0	1.7	1.5	−0.1
	(2.1, 3.9)	(2.2, 3.7)	(−0.8, 0.8)	(1.3, 2.0)	(1.1, 1.9)	(−0.5, 0.2)
CL/F	287	264	−23
(l h−1)	(140, 434)	(199, 328)	(−157, 110)

t_max, t_1/2 and CL/F values indicate geometric means. GFJ–water value indicates difference between GFJ and water. Values in parentheses represent 95% confidence intervals.

^*P < 0.05;

^†P < 0.01;

^‡P < 0.001.

Average AUC(0,48 h), AUC(0, ∞) and C_max of atorvastatin lactone in plasma increased 1.56 fold (95% CI 1.33, 1.83; P < 0.001), 1.63 fold (95% CI 1.40, 1.89; P < 0.001), and 1.29 fold (95% CI 1.09, 1.51; P < 0.01), respectively, when GFJ was taken with atorvastatin. Furthermore, average and t_1/2 values were significantly prolonged by 4.2 h (95% CI 1.2, 7.2; P < 0.05) and 3.0 h (95% CI 1.1, 5.0; P < 0.05), respectively. No significant changes were detected in t_max (Figure 1, Tables 1 and 2).

Average AUC(0,48 h) and C_max of 2-hydroxyatorvastatin acid decreased 0.34 fold (95% CI 0.15, 0.81; P < 0.05) and 0.34 fold (95% CI 0.21, 0.56; P < 0.01), respectively, when GFJ was taken with atorvastatin. Furthermore, average t_max, , and t_1/2 were significantly prolonged by 10.1 h (95% CI 9.1, 11.1; P < 0.001), 14.0 h (95%CI 8.3, 19.7; P < 0.01), and 6.9 h (95% CI 2.1, 11.8; P < 0.05), respectively. No significant changes were detected in AUC(0, ∞) (Figure 2, Tables 1 and 2).

Figure 2.

Plasma concentrations (mean ± SD) of 2-hydroxyatorvastatin acid (above) and 2-hydroxyatorvastatin lactone (below) after a single 10 mg dose of atorvastatin. Water intake group (○); GFJ intake group (•)

Average AUC(0,48 h) and C_max of 2-hydroxyatorvastatin lactone decreased 0.80 fold (95% CI 0.67, 0.95; P < 0.05) and 0.67 fold (95% CI 0.56, 0.80; P < 0.001), respectively, when GFJ was taken with atorvastatin. Furthermore, average t_max, , and t_1/2 significantly increased by 4.0 h (95% CI 1.8, 6.2; P < 0.01), 12.3 h (95% CI 7.1, 17.5; P < 0.001), and 6.3 h (95% CI 3.0, 9.6; P < 0.01), respectively. No significant changes were detected in AUC(0, ∞) (Figure 2, Tables 1 and 2).

Study II

GFJ did not produce any significant effects on any pravastatin pharmacokinetic parameter measured (Figure 3, Tables 1 and 2).

Figure 3.

Plasma concentrations (mean ± SD) of pravastatin (above) and pravastatin lactone (below) after a single 10 mg dose of pravastatin. Water intake group (○); GFJ intake group (•)

Although mean AUC(0,24 h) of pravastatin lactone was increased 1.31 fold (95% CI 1.01, 1.71; P < 0.05) when GFJ was taken with pravastatin, no significant change was detected in average AUC(0, ∞). Furthermore, average t_max increased by 0.4 h (95% CI 0.0, 0.8; P < 0.05). No significant changes were detected in the other parameters measured (Figure 3, Tables 1 and 2).

Discussion

The present results suggest that repeated GFJ intake significantly affects the pharmacokinetics of atorvastatin acid and its three metabolites, whereas it does not cause any significant effects on pravastatin disposition and only slightly affects that of pravastatin lactone.

GFJ contains CYP3A4 inhibitors such as furanocoumarin derivatives [1–3] that bind to CYP3A4 present in small intestine epithelial cells. When taken with GFJ, drugs that are normally metabolized by CYP3A4 and that have low oral availability exhibit increased plasma concentrations [4]. In addition, repeated intake of GFJ selectively down-regulates small intestine CYP3A4 activity [15]. As a pilot study of the present study, the inhibitory effects of each GFJ lot used in the present study were examined on CYP3A4 metabolic activity (6β-hydroxytestosterone production activity). No differences in the inhibitory effects on metabolic activity of CYP3A4 were detected in the two lots used in the two studies.

It was recently reported that increases in the plasma concentrations of cyclosporin A caused by GFJ intake are not elicited by CYP3A4 inhibition but rather caused by inhibition of excretion of this molecule to the GI tract mediated by P-glycoprotein transporters [7]. In general, CYP3A4 substrates are also likely to be P-glycoprotein substrates [16]. Atorvastatin is one such substrate of P-glycoprotein transporters [17]; pravastatin is not [18]. In the present study, however, the effect of GFJ on P-glycoprotein transporters in the intestinal tract was suggested to be minor, since no effects of GFJ were observed on C_max of atorvastatin acid and atorvastatin has a lower affinity for the transporter than other HMG-CoA reductase inhibitors such as lovastatin and simvastatin [17]. Hence the effects of repeated ingestion of GFJ observed in the present study are likely mostly due to CYP3A4 inhibition elicited in the small intestine.

Besides the small intestine, most drug metabolism by CYP3A4 takes place in the liver. In the present study, since the plasma concentration of 2-hydroxyatorvastatin acid was kept under the detection limit for several hours by repeated GFJ intake, it is suggested that repeated GFJ intake induces strong CYP3A4 inhibition and that CYP3A4 metabolizes atorvastatin mainly in the small intestine during the early stages of absorption.

The elimination t_1/2 values of atorvastatin lactone, 2-hydroxyatorvastatin acid, and 2-hydroxyatorvastatin lactone but not atorvastatin acid were significantly increased during the GFJ vs the water phase. These results are similar to those obtained by Lilja et al.[13] who speculated that inhibition of P-glycoprotein or down-regulation of CYP3A4 might be a causative factor. In this study, however, we assumed the inhibition of P-glycoprotein was minor, so down-regulation of CYP3A4 could be the possible explanation. CYP-dependent metabolism of atorvastatin lactone to its hydroxy metabolite is significantly higher than that of the acid form, and since the lactone is a strong competitive inhibitor of atorvastatin acid metabolism, 2-hydroxyatorvastatin acid may be mainly formed from interconversion of 2-hydroxatorvastatin lactone in vivo[14]. These differences in substrate specificity and the apparent metabolic equilibrium between acid and lactone might contribute to the observed increases in the elimination t_1/2 values of lactone form.

AUC(0,48 h) and AUC(0, ∞) of atorvastatin lactone were 55% and 82%, respectively, of those of atorvastatin acid. Since repeated GFJ intake inhibited the conversion of atorvastatin lactone to 2-hydroxyatorvastatin lactone in the present study, atorvastatin lactone is suggested to be formed mainly in the GI tract.

In vitro studies using liver microsomes and studies on the concomitant use of CYP3A4 inhibitors (itraconazole, diltiazem) with pravastatin have shown that pravastatin metabolism is not affected by such inhibitors [19–21]. The present results appear to confirm that pravastatin is not metabolized by CYP3A4 located in the small intestine, since repeated GFJ intake did not significantly affect the pharmacokinetics of pravastatin. Although AUC(0,24 h) and t_max of pravastatin lactone significantly increased following repeated GFJ intake, AUC(0, ∞) was not significantly affected. In addition, AUC(0,24 h) and AUC(0, ∞) of pravastatin lactone were only about 5% and 6%, respectively, of those of pravastatin when pravastatin was taken without GFJ. AUC(0,24 h) and AUC(0, ∞) of pravastatin lactone were increased by approximately 31% (P < 0.05) and 25% (NS), respectively, following repeated GFJ intake, indicating that these parameters were <1/10 of those of pravastatin. Thus the effects of repeated GFJ intake on the pharmacokinetics of pravastatin are presumed to be small in comparison with the effects on atorvastatin.

Several clinical pharmacological investigations have been conducted on drug interactions between GFJ and HMG-CoA reductase inhibitors. C_max of the lipid-soluble HMG-CoA reductase inhibitors simvastatin and lovastatin were reported to increase 8.4 and 10.8 fold, respectively, and AUC of both drugs more than 10 fold, with repeated GFJ intake [11, 12]. AUC(0,72 h) of atorvastatin acid has been reported to increase 2.5 fold when atorvastatin is taken with repeated GFJ intake [13]. On the other hand, the pharmacokinetics of the water-soluble HMG-CoA reductase inhibitor pravastatin are not affected by repeated GFJ intake [13].

The present study is the first clinical pharmacological study on drug interactions between GFJ and HMG-CoA reductase inhibitors conducted in Japanese subjects. The result that plasma concentrations of atorvastatin and the hydroxide metabolites of atorvastatin lactone are decreased, due to inhibition of formation, by repeated GFJ intake is approximately consistent with the results of a similar study carried out in Finland [13]. However, in the present study the plasma concentrations of atorvastatin and atorvastatin lactone did not increase as much as in the Finnish study. A possible cause of this dissimilarity could be due to differences in the GFJ used [22], the amount administered, or ethnic factors. In the Finnish study, 200 ml of double-strength GFJ was used per administration, whereas in the present study we used 250 ml of 100% GFJ from concentrate per administration, leading to the possibility that the consumed CYP3A4 inhibitor content may have been less in our study. However, since 2-hydroxyatorvastatin acid formation was strongly inhibited in the present study as well as in the prior study, it seems that the amount of GFJ taken in the present study was enough to fully saturate the small intestinal CYP3A4 inhibition effect.

The dose of study drugs administered in the present study was 1/4 of that used in the Finnish study. Any amount of the study drug that is absorbed without being metabolized by CYP3A4 located in the small intestine is metabolized, before entering the circulation, by CYP3A4 located in the liver. Hence if the liver metabolism is nonlinear, there is a possibility of explain-ing the response difference in the two studies by the difference in dose; however, there have been no re-ports, so far, indicating nonlinear liver metabolism of atorvastatin.

Another difference that could be a contributing factor is ethnicity. The study in Finland included Caucasians who may possibly have different CYP3A4 expression levels or activities from those of Japanese subjects. However, it has been reported that both CYP3A4 protein levels in the liver and CYP3A4 activity as measured using nifedipine oxidation as an index are not different between Caucasian and Japanese subjects [23]. Moreover, there have been no reports that the expression or activity of CYP3A4 located in the small intestine differ between these two ethnic groups. Further investigations are required to clarify the different results observed in the Finnish and present studies.

Since repeated GFJ intake does not appear to affect the pharmacokinetics of pravastatin, it does not seem necessary to exercise caution in this respect when prescribing this drug. However, repeated GFJ intake significantly increased AUC(0,48 h) of atorvastatin acid in healthy volunteers, and thus patients on atorvastatin should be advised to avoid ingesting GFJ, especially in large quantities.