- Email: [email protected]
Role of Organic Anion Transporting Polypeptide 2 in Pharmacokinetics of Digoxin and β-Methyldigoxin in Rats
Role of Organic Anion Transporting Polypeptide 2 in Pharmacokinetics of Digoxin and b-Methyldigoxin in Rats SACHIYO FUNAKOSHI,1,2 TERUO MURAKAMI,1 RYOKO YUMOTO,1 YOSHIE KIRIBAYASHI,2 MIKIHISA TAKANO1 1
Department of Pharmaceutics and Therapeutics, Programs for Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan 2
Department of Pharmacy, Chugoku Rousai Hospital, 1-5-1 Hiro-Tagaya, Kure City, Hiroshima 737-0193, Japan
Received 29 October 2004; revised 8 February 2005; accepted 11 February 2005 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.20346
ABSTRACT: Recently, we found that potent P-glycoprotein (P-gp) inhibitors, such as verapamil and cyclosporin A, markedly modulated the pharmacokinetics of digoxin in rats, whereas they did not affect b-methyldigoxin pharmacokinetics significantly. Digoxin is also a substrate of rat organic anion transporting polypeptide 2 (Oatp2). Here, we compared the magnitude of Oatp2-mediated drug interaction of digoxin and bmethyldigoxin using amiodarone as an Oatp2 inhibitor in rats. Amiodarone (20 mg/kg) given intravenously significantly increased plasma levels and decreased biliary excretion, liver distribution, and intestinal distribution of digoxin administered intravenously at a dose of 10 mg/kg. Amiodarone also significantly decreased biliary excretion and liver distribution of b-methyldigoxin, but the change in plasma levels of b-methyldigoxin was quite small. These findings may give a clue in selecting these cardiac glycosides in clinical pharmacotherapy for patients receiving multiple drugs towards escape from Oatp2mediated drug interactions. ß 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1196–1203, 2005
Keywords: organic anion-transporting polypeptide 2 (Oatp2); digoxin; b-methyldigoxin; drug interaction; amiodarone
INTRODUCTION Since the discovery of digitalis glycosides or extracts of the common foxglove plant (Digitalis purourea) as medicine in 1775 by Scottish doctor William Withering, digoxin has been widely used in cardiology as the safe inotropic drug.1–3 Derivatives of digoxin, such as a-methyldigoxin, bmethyldigoxin, and b-acetyldigoxin, have been developed to increase the intestinal absorption of digoxin. These derivatives have the same mechanism of action and potencies with digoxin, but have significantly higher oral bioavailabilities
Correspondence to: Mikihisa Takano (Telephone: 81-82257-5315; Fax: 81-82-257-5319; E-mail: [email protected]) Journal of Pharmaceutical Sciences, Vol. 94, 1196–1203 (2005) ß 2005 Wiley-Liss, Inc. and the American Pharmacists Association
1196
than digoxin in humans. Both digoxin and bmethyldigoxin are commonly prescribed in Japan in the treatment of congestive heart failure and other congestive states. The recommended maintenance doses of oral digoxin and b-methyldigoxin are, respectively, 0.125–0.5 and 0.05– 0.2 mg/day, which are depending on their oral bioavailabilities.4,5 Many compounds induce drug interactions when coadministered with digoxin clinically.6 Digoxin is a substrate of P-glycoprotein (P-gp) and the drug interactions of digoxin with various compounds, such as quinidine, verapamil, nifedipine, and rifampicin, are now explained by P-gp-mediated drug interaction.7–10 P-gp, an ATP-dependent efflux pump, is expressed in various normal human and rodent tissues, including the intestine, liver, kidney, adrenal gland, brain, eye, and testis.11,12 In these tissues, P-gp
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
OATP2-MEDIATED DRUG INTERACTION
limits the entry and/or accumulation of endogenous and exogenous P-gp substrates such as steroid hormones, anticancer agents, immunosuppressive agents, calcium channel blockers, b-blockers, and so on.13,14 In contrast, the involvement of P-gp in b-methyldigoxin pharmacokinetics was unclear, although other cardiac glycosides, such as digitoxin, a-methyldigoxin, and b-acetyldigoxin, are reportedly P-gp substrates.15 In the previous report, we compared the magnitudes of P-gp-mediated drug interaction of digoxin and bmethyldigoxin pharmacokinetically using wellknown P-gp inhibitors, verapamil and cyclosporin A, in rats. In that study, we found that P-gpmediated drug interactions can easily occur in digoxin, but hardly in b-methyldigoxin.16 In addition to P-gp, digoxin is also known as a substrate of rat organic anion transporting polypeptide 2 (Oatp2).17–19 Oatp2 has a broad substrate specificity and accepts various organic anions and cations, in addition to cardiac glycosides such as digoxin and ouabain. Oatp2 is predominantly expressed at the sinusoidal membrane in perivenous hepatocytes, and in the brain and retina to some extent.19–22 Some Oatp2related compounds, such as indomethacin and amiodarone, also cause drug interactions with digoxin in humans.23–26 The interaction of digoxin with indomethacin has been found in infants, elderly, or patients with renal failure, which resulted in a significant elevation of serum digoxin levels.25–27 The interaction with amiodarone has been observed even in normal subjects under usual dosage regimen, in which renal and nonrenal clearances of digoxin are reduced significantly.23,24,28–30 In the interaction of digoxin with indomethacin, however, the contribution of Oatp2-mediated interaction may be small, if any, because the inhibitory potency of indomethacine on Oatp2-mediated digoxin transport is weak (>100 mM). In addition, the plasma unbound concentration of indomethacin is low, because of high plasma protein binding (>96%).18 On the other hand, amiodarone is a potent Oatp2 inhibitor with a Ki value of 1.8 mM, as estimated by digoxin uptake in Xenopus oocytes.31 Amiodarone is also known as a P-gp inhibitor and its Ki value for human P-gp is reportedly 45.6 mM, which was estimated from digoxin transport study in MDR1expressing LLC-PK1 cells.32 It is reported that amiodarone inhibits the uptake of digoxin into hepatocytes and increases its blood levels in rats.24 Regarding the interaction between digoxin and amiodarone, Kodawara et al. reported that Oatp2
1197
rather than P-gp may be one of the interaction sites, based on in vitro transport study using P-gpexpressing LLC-GA5-COL 150 cell monolayers and Oatp2-expressing Xenopus oocytes.31 In the present study, we compared the magnitudes of Oatp2-mediated drug interaction of digoxin and b-methyldigoxin pharmacokinetically by using amiodarone as an Oatp2 inhibitor in rats. The involvement of Oatp2 in b-methyldigoxin pharmacokinetics is unclear so far. Present study is expected to give a clue in selecting cardiac glycosides in clinical pharmacotherapy towards escape from P-gp- and/or Oatp2-mediated drug interactions.
MATERIALS AND METHODS Materials Digoxin was obtained from Sigma-Aldrich Company/Japan (Tokyo, Japan). b-Methyldigoxin was a gift from Nippon Roche (Kanagawa, Japan). Amiodarone was purchased from Sigma-Aldrich Company/Japan. Dulbecco’s-phosphate buffered saline (D-PBS) was from Gibco Laboratories (Life Technologies, Inc., NY). All other chemicals used were of the highest purity available. Animals Male Wistar rats weighing 220–300 g (8–9 weeks old) were fasted overnight with free access to water before the experiments. Animal experiments were performed in accordance with the Guide for Animal Experimentation from the Committee of Research Facilities for Laboratory Animal Sciences, Graduate School of Biomedical Sciences, Hiroshima University. In Vivo Pharmacokinetics Rats were fasted overnight, anesthetized with pentobarbital (30 mg/kg intraperitoneal injection), and affixed supine on a surface kept at 378C. In vivo pharmacokinetic studies of cardiac glycosides were performed in a similar manner as reported previously.16 Briefly, cannulation was made with polyethylene tubing (PE-50) at a femoral vein and a femoral artery, respectively. The urinary bladder and bile duct were also cannulated with polyethylene tubing PE-50 and PE-10, respectively. Digoxin and b-methyldigoxin were dissolved in pH 7.4 phosphate buffer containing 5% ethanol at a concentration of 5 mg/ml, JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
1198
FUNAKOSHI ET AL.
and the solution was administered by bolus injection via the cannula inserted at the femoral vein at a dose of 10 mg/kg. Blood was collected via the cannula inserted at the femoral artery at 5, 10, 30, 60, 120, 180, and 240 min after administration of a cardiac glycoside. Bile was collected serially via the cannula at 60, 120, and 240 min after administration. Urine was collected continuously via the cannula for 240 min. In inhibition study, amiodarone was dissolved in 30% ethanol-aqueous solution at a concentration of 5 mg/ml, and the solution was injected intravenously via the cannula 10 min prior to the administration of a cardiac glycoside. The dose of amiodarone was 5 or 20 mg/kg. Sampling of blood, bile, and urine was carried out in the same time schedules as described above. Plasma was separated from blood by centrifugation to determine plasma concentration of a cardiac glycoside. The area under the plasma concentration-time curves (AUC) was estimated by a trapezoidal rule using plasma levels of a drug until 240 min (AUC0–240), and in vivo total plasma clearance (CLtotal) was calculated by dividing the intravenous dose by AUC0–240 of a drug. In Vivo Tissue Distribution Separately, tissue distribution of two cardiac glycosides was determined in untreated control and amiodarone-treated, anesthetized rats. In case of inhibition study, rats received amiodarone (20 mg/kg) intravenously at first, then a cardiac glycoside (10 mg/kg) intravenously from the tail vein. Rats were exsanguined by decaptation to isolate the liver, heart, lung, and/or intestine 30 min after injection of a cardiac glycoside. Blood was also collected at the same time. Isolated tissue was homogenized with a three- to ninefold volume of distilled water, and the homogenate was centrifuged at 3000 rpm for 10 min to obtain the supernatant. Blood was centrifuged at 3000 rpm for 10 min to obtain plasma sample. The tissue distribution of a cardiac glycoside was expressed as the ratio of concentration in the tissue against that in plasma (T/P ratio). Analysis Concentrations of digoxin and b-methyldigoxin in biological fluids (plasma, bile, urine, supernatant of tissue homogenate) were determined by a fluorescence polarization immunoassay (FPIA, TDX1, Dainabot Co., Ltd., Tokyo, Japan) after JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
diluting the sample appropriately to a concentration range from 0.2 to 4.0 ng/ml. Values were expressed as the mean SE. Treatment groups were compared by two-tailed Student’s t-test for unpaired samples. A p-value of less than 0.05 was considered statistically significant.
RESULTS Effect of Amiodarone on Pharmacokinetics of Digoxin and b-Methyldigoxin Amiodarone at a dose of 20 mg/kg significantly increased plasma levels of digoxin given intravenously, whereas amiodarone at a dose of 5 mg/kg did not show any significant effect (Figure 1A). In contrast, the effect of amiodarone on plasma levels of b-methyldigoxin was observed only in initial 10 min even at a dose of 20 mg/kg (Figure 1B). In Table 1, AUC0–240 and CLtotal of these cardiac glycosides in untreated control and amiodarone-treated rats were summarized. Amiodarone (20 mg/kg) increased the AUC0–240 of digoxin by more than twofold, whereas it did not affect AUC0–240 of b-methyldigoxin significantly. Effect of amiodarone on biliary excretion of digoxin and b-methyldigoxin is shown in Figure 2. The biliary excretion of these cardiac glycosides during 4 h after intravenous administration was almost the same extents in untreated control rats. On one hand, the initial excretion rate of digoxin was approximately 1.8-fold higher than that of bmethyldigoxin, suggesting some difference in the liver uptake rate between them. Treatment with amiodarone decreased the biliary excretion of both digoxin and b-methyldigoxin in a dose-dependent manner. At 4 h after administration, amiodarone (20 mg/kg) inhibited the cumulative biliary excretion of digoxin by 54% and that of b-methyldigoxin by 77%. The effect of amiodarone on urinary excretion of digoxin and b-methyldigoxin is shown in Figure 3. Amiodarone (20 mg/kg) significantly inhibited the urinary excretion of digoxin, though the urinary excretion of digoxin was quite small in rats. Amiodarone did not affect the urinary excretion of b-methyldigoxin significantly. Effect of Amiodarone on Tissue Distribution of Digoxin and b-Methyldigoxin The effect of amiodarone (20 mg/kg) on tissue distribution of cardiac glycosides was evaluated in
OATP2-MEDIATED DRUG INTERACTION
1199
Figure 1. Plasma concentration-time profiles of digoxin and b-methyldigoxin given intravenously at a dose of 10 mg/kg in untreated control (*), amiodarone (5 mg/kg)treated (~), and amiodarone (20 mg/kg)-treated (*) rats. Amiodarone was administered intravenously 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). *Significantly different between the untreated control and amiodarone (20 mg/kg)-treated rats at a level of p < 0.05.
the liver, lung, kidney, and intestine (Table 2). In untreated control rats, both cardiac glycosides distributed to the liver preferentially. Digoxin also distributed to the intestine at a higher extent as compared with those to the heart and lung. bMethyldigoxin evenly distributed to the lung, heart, and intestine. Amiodarone significantly decreased the liver distribution of both cardiac glycosides to approximately 20–30% of control. Also, amiodarone decreased the intestinal distribution of digoxin by approximately 60%, but not of b-methyldigoxin.
DISCUSSION The pharmacokinetics of digoxin is known to be susceptible to many commonly prescribed drugs including antipyretic/analgesic agents, anti-arrhythmic agents, calcium channel blockers, steroid hormones, immunosuppressants, chemotherapeutic drugs, antibiotics, proton pump inhibitors, and so on.33–35 Most of these interactions with digoxin are explained by P-gpmediated drug interactions. In clinical therapy, such drug interactions with digoxin often occur in
Table 1. AUC0–4 and CLtotal, 0–4 of Digoxin and b-Methyldigoxin After Intravenous Administration at a Dose of 10 mg/kg in Untreated Control and Amiodarone-Treated Rats AUC0–4 (ng min/mL) Digoxin þAmiodarone (5 mg/kg) þAmiodarone (20 mg/kg) b-Methyldigoxin þAmiodarone (5 mg/kg) þAmiodarone (20 mg/kg)
304.0 32.6 397.2 84.6 730.0 11.3* 1016 80 1230 14 1254 207
CLtotal,
0–4
(mL/min/kg)
35.7 4.4 26.5 6.4 14.1 2.4* 10.1 0.9 8.1 0.1 8.2 1.5
Amiodarone was administered intravenously at a dose of 5 or 20 mg/kg 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). *Significantly different from digoxin alone at a level of p < 0.05. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
1200
FUNAKOSHI ET AL.
Figure 2. Biliary excretion-time profiles of digoxin and b-methyldigoxin given intravenously at a dose of 10 mg/kg in untreated control (*), amiodarone (5 mg/kg)treated (~), and amiodarone (20 mg/kg)-treated (*) rats. Amiodarone was administered intravenously 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). *Significantly different between the untreated control and amiodarone (20 mg/kg)-treated rats at a level of p < 0.05.
the elderly, in neonates, and in patients with renal dysfunction. It is important to clarify the molecular mechanisms of such drug interactions in order to predict and avoid the interactions. In contrast to digoxin, information on b-methyldigoxin is quite limited. Previously, we compared the magnitude of P-gp-mediated drug interaction of digoxin and b-methyldigoxin using potent P-gp
inhibitors, verapamil and cyclosporin A.16 In that study, P-gp-mediated drug interactions occurred easily in digoxin, but hardly in b-methyldigoxin. Digoxin is also known as a substrate of Oatp2, or human OATP8, and possibly of Oatp3,36,37 though it is unknown whether b-methyldigoxin is also recognized as a substrate by Oatp2. Here, we compared the possible Oatp2-mediated drug
Figure 3. Urinary excretion of digoxin and b-methyldigoxin during 4 h after intravenous administration at a dose of 10 mg/kg in untreated control (&), amiodarone (5 mg/kg)-treated ( ), and amiodarone (20 mg/kg)-treated (&) rats. Amiodarone (AMD) was administered intravenously 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
OATP2-MEDIATED DRUG INTERACTION
1201
Table 2. Effect of Amiodarone on Tissue Distribution (Tissue-To-Plasma Concentration Ratio) of Digoxin and b-Methyldigoxin in Rats
Digoxin þAmiodarone (20 mg/kg) b-Methyldigoxin þAmiodarone (20 mg/kg)
Liver
Lung
Heart
Intestine
14.7 6.8 4.5 0.8* 10.5 1.6 2.6 0.8*
2.10 0.12 1.76 0.09 1.60 0.17 1.32 0.13
2.46 0.06 2.76 0.34 1.83 0.31 1.53 0.18
5.86 0.78 2.22 0.20* 1.55 0.50 1.25 0.24
Amiodarone was administered intravenously at a dose of 20 mg/kg 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3). *Significantly different from digoxin alone at a level of p < 0.05.
interaction of digoxin and b-methyldigoxin pharmacokinetically, using amiodarone as an Oatp2 inhibitor in rats. Amiodarone is a Class III antiarrhythmic agent, and its clinical use is generally restricted to the treatment of drug-resistant arrhythmias because of serious adverse effects. Amiodarone is also known to cause drug interactions with various drugs including digoxin, warfarin, procainamide, lidocaine, cyclosporin, quinidine, and so on.23,24,28–30,38 –40 Regarding the interaction between digoxin and amiodarone, Kodawara et al. recently proposed the Oatp2-mediated drug interaction, rather than P-gp-mediated, based on in vitro studies as described in the Introduction section.31 In good agreement with their report, amiodarone (20 mg/kg, i.v.) decreased the distribution of digoxin and b-methyldigoxin to the liver, where Oatp2 is expressed (Figure 2 and Table 2). The decrease in liver distribution and consequent biliary excretion of these cardiac glycosides would be probably due to the Oatp2-mediated drug interaction, because P-gp-mediated drug interaction in b-methyldigoxin pharmacokinetics can be ruled out as reported previously.16 In the present study, a marked difference was observed in the effect of amiodarone on plasma levels between digoxin and b-methyldigoxin. Amiodarone (20 mg/kg) significantly increased plasma AUC0–4 of digoxin by 2.4-fold of control, whereas the effect on plasma AUC0–4 of bmethyldigoxin was quite small (1.2-fold) (Table 1). It is difficult to explain the discrepancy between the effects of amiodarone on the liver distribution and the plasma level of these cardiac glycosides. The lower tissue distribution of b-methyldigoxin than digoxin in the early stage (distribution phase) (Figure 1 and Table 2) may be related to the lesser effect of reduced biliary excretion on plasma bmethyldigoxin level, at least partly. Further study is necessary to clarify the different effects of
amiodarone on plasma profiles of digoxin and bmethyldigoxin. As described in the Introduction section, the interaction of digoxin with amiodarone has been observed frequently in humans.23,24,28–30 On one hand, there is a species difference in elimination pathways of digoxin and b-methyldigoxin between rats and humans. For example, more than 30% of dose of these cardiac glycosides is recovered in urine within 24 h in humans.41–43 Thus, there may be some differences in the extent of hepatic distribution of these cardiac glycosides between rats and humans, although digoxin is recognized by human OATP8 (SLC21A8) and OATP8 is localized to the sinusoidal membrane of hepatocytes in humans, as well as in rats.44,45 In addition, the protein binding of amiodarone is very high (more than 96% or more than 99.9% in average, depending on literatures),46,47 indicating that the concentration of unbound amiodarone is very low in plasma. The maximal plasma concentration of amiodarone given intravenously at a dose of 20 mg/ kg would be less than 15 mM, though the plasma level would be kept for very long time, according to the literatures.46–48 Thus, there is a difference between the reported Ki value (1.8 mM) of amiodarone on Oatp2 and possible unbound concentration of amiodarone in the present study. It may be due to the extensive tissue distribution of amiodarone, which inhibits the transporter more potently than expected based on its unbound plasma concentration. To explain the interaction mechanism(s) between cardiac glycosides and amiodarone completely, further studies, including other pharmacokinetic interactions than Oatp2mediated transport, would be necessary by taking the above points into consideration. In conclusion, we compared the magnitude of Oatp2-mediated drug interaction of digoxin and b-methyldigoxin in rats. Amiodarone, a potent Oatp2 inhibitor, decreased the distribution of JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
1202
FUNAKOSHI ET AL.
these cardiac glycosides to the liver and their biliary excretions. On the other hand, amiodarone modified plasma levels of digoxin significantly, but not of b-methyldigoxin. Collectively, the present and our previous findings16 may give a clue in selecting these cardiac glycosides in clinical pharmacotherapy for patients taking multiple drugs, towards escape from P-gp- and/or Oatp2-mediated drug interactions.
14.
REFERENCES
16.
1. Friend DG. 1976. Digitalis after two centuries (William Withering). Arch Surg 111:14–19. 2. Hauptman PJ, Kelly RA. 1999. Digitalis. Circulation 99:1265–1270. 3. Kjeldsen K, Bundgaard H. 2003. Myocardial Na,KATPase and digoxin therapy in human heart failure. Ann NY Acad Sci 986:702–707. 4. Ito Y, Seki K, Kimura E. 1975. Multiclinical open studies on the effect of beta-methyldigoxin on congestive heart failure with atrial fibrillation. Jpn Heart J 16:538–547. 5. Das G. 1989 Beta-methyl digoxin: A better absorbable digoxin. Int J Clin Pharmacol Ther Toxicol 27: 521–525. 6. Marcus FI. 1985. Pharmacokinetic interactions between digoxin and other drugs. J Am Coll Cardiol 5:82–90. 7. De Lannoy IA, Silverman M. 1992. The MDR1 gene product, P-glycoprotein, mediates the transport of the cardiac glycoside, digoxin. Biochem Biophys Res Commun 189:551–557. 8. Fromm MF, Kim RB, Stein CM, Wilkinson GR, Roden DM. 1999. Inhibition of P-glycoproteinmediated drug transport: A unifying mechanism to explain the interaction between digoxin and quinidine. Circulation 99:552–557. 9. Verschraagen M, Koks CH, Schellens JH, Beijnen JH. 1999. P-glycoprotein system as a determinant of drug interactions: The case of digoxin-verapamil. Pharmacol Res 40:301–306. 10. Greiner B, Eichelbaum M, Fritz P, Kreichgauer H-P, von Richter O, Zundler J, Kroemer HK. 1999. The role of intestinal P-glycoprotein in the interaction of digoxin and rifampin. J Clin Invest 104:147– 153. 11. Thiebaut F, Tsuruo T, Hamada H, Gottesman MM, Pastan I, Willingham MC. 1987. Cellular localization of the multidrug-resistance gene product P-glycoprotein in normal human tissues. Proc Natl Acad Sci USA 84:7735–7738. 12. Holash JA, Stewart PA. 1993. The relationship of astrocyte-like cells to the vessels that contribute to the blood-ocular barriers. Brain Res 629:218–224. 13. Hunter J, Jepson MA, Tsuruo T, Simmons NL, Hirst BH. 1993. Functional expression of P-glyco-
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
15.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
protein in apical membranes of human intestinal Caco-2 cells. Kinetics of vinblastine secretion and interaction with inhibitors. J Biol Chem 268: 14991–14997. Tsuji A, Tamai I. 1996. Carrier-mediated intestinal transport of drugs. Pharm Res 13:963–977. Pauli-Magnus C, Mu¨rdter T, Godel A, Mettang T, Eichelbaum M, Klotz U, Fromm MF. 2001. P-glycoprotein-mediated transport of digitoxin, a-methyldigoxin and b-acetyldigoxin. NaunynSchmiedeberg’s Arch Pharmacol 363:337–343. Funakoshi S, Murakami T, Yumoto R, Kiribayashi Y, Takano M. 2003. Role of P-glycoprotein in pharmacokinetics and drug interactions of digoxin and beta-methyldigoxin in rats. J Pharm Sci 92: 1455–1463. Noe B, Hagenbuch B, Stieger B, Meier PJ. 1997. Isolation of a multispecific organic anion and cardiac glycoside transporter from rat brain. Proc Natl Acad Sci USA 94:10346–10350. Shitara Y, Sugiyama D, Kusuhara H, Kato Y, Abe T, Meier PJ, Itoh T, Sugiyama Y. 2002. Comparative inhibitory effects of different compounds on rat oatpl (slc21a1)- and Oatp2 (Slc21a5)-mediated transport. Pharm Res 19:147–153. Sugiyama D, Kusuhara H, Shitara Y, Abe T, Sugiyama Y. 2002. Effect of 17 beta-estradiolD-17 beta-glucuronide on the rat organic anion transporting polypeptide 2-mediated transport differs depending on substrates. Drug Metab Dispos 30:220–223. Gao B, Stieger B, Noe B, Fritschy JM, Meier PJ. 1999. Localization of the organic anion transporting polypeptide 2 (Oatp2) in capillary endothelium and choroid plexus epithelium of rat brain. J Histochem Cytochem 47:1255–1264. Gao B, Wenzel A, Grimm C, Vavricka SR, Benke D, Meier PJ, Reme CE. 2002. Localization of organic anion transport protein 2 in the apical region of rat retinal pigment epithelium. Invest Ophthalmol Vis Sci 43:510–514. van Montfoort JE, Schmid TE, Adler ID, Meier PJ, Hagenbuch B. 2002. Functional characterization of the mouse organic-anion-transporting polypeptide 2. Biochim Biophys Acta 1564:183–188. Oetgen WJ, Sobol SM, Tri TB, Heydorn WH, Rakita L. 1984. Amiodarone-digoxin interaction. Clinical and experimental observations. Chest 86:75–79. Lambert C, Lamontagne D, Hottlet H, du Souich P. 1989. Amiodarone-digoxin interaction in rats. A reduction in hepatic uptake. Drug Metab Dispos 17:704–708. Jorgensen HS, Christensen HR, Kampmann JP. 1991. Interaction between digoxin and indomethacin or ibuprofen. Br J Clin Pharmacol 31:108– 110. Haig GM, Brookfield EG. 1992. Increase in serum digoxin concentrations after indomethacin therapy
OATP2-MEDIATED DRUG INTERACTION
27.
28.
29. 30.
31.
32.
33.
34.
35.
36.
37.
in a full-term neonate. Pharmacotherapy 12:334– 336. Johnson AG, Seidemann P, Day RO. 1994. NSAIDrelated adverse drug interactions with clinical relevance. An update. Int J Clin Pharmacol Ther 32:509–532. Fenster PE, White NW, Jr., Hanson CD. 1985. Pharmacokinetic evaluation of the digoxin-amiodarone interaction. J Am Coll Cardiol 5:108–112. Lesko LJ. 1989. Pharmacokinetic drug interactions with amiodarone. Clin Pharmacokinet 17:130–140. Freitag D, Bebee R, Sunderland B. 1995. Digoxinquinidine and digoxin-amiodarone interactions: Frequency of occurrence and monitoring in Australian repatriation hospitals. J Clin Pharm Ther 20:179–183. Kodawara T, Masuda S, Wakasugi H, Uwai Y, Futami T, Saito H, Abe T, Inu K. 2002. Organic anion transporter oatp2-mediated interaction between digoxin and amiodarone in the rat liver. Pharm Res 19:738–743. Katoh M, Nakajima M, Yamazaki H, Yokoi T. 2001. Inhibitory effects of CYP3A4 substrates and their metabolites on P-glycoprotein-mediated transport. Eur J Pharm Sci 12:505–513. Davis TD, Vanderveen RL, Nienhuis M. 1983. Digoxin. In: Mungall DR, editor. Applied clinical pharmacokinetics. New York: Raven Press. pp 79– 102. Rodin SM, Johnson BF. 1988. Pharmacokinetic interactions with digoxin. Clin Pharmacokinet 15: 227–244. Nolan PE, Jr., Raehl CL, Zarembski DG. 1996. Congestive heart failure. In: Herfindal ET, Gourley DR, editors. Textbook of therapeutics drug and disease management: Cardiovascular disorders. Section 10. 6th edition. Baltimore: Williams & Wilkins. pp 729–761. Cattori V, van Montfoort JE, Stieger B, Landmann L, Meijer DK, Winterhalter KH, Meier PJ, Hagenbuch B. 2001. Localization of organic anion transporting polypeptide 4 (Oatp4) in rat liver and comparison of its substrate specificity with Oatp1, Oatp2 and Oatp3. Pflugers Arch 443:188–195. Hagenbuch B, Meier PJ. 2003. The superfamily of organic anion transporting polypeptides. Biochim Biophys Acta 1609:1–18.
1203
38. Heimark LD, Wienkers L, Kunze K, Gibaldi M, Eddy AC, Trager WF, O’Reilly RA, Goulart DA. 1992. The mechanism of the interaction between amiodarone and warfarin in humans. Clin Pharmacol Ther 51:398–407. 39. Nicolau DP, Uber WE, Crumbley AJ 3rd, Strange C. 1992. Amiodarone-cyclosporine interaction in a heart transplant patient. J Heart Lung Transplant 11:564–568. 40. Ha HR, Candinas R, Stieger B, Meyer UA, Follath F. 1996. Interaction between amiodarone and lidocaine. J Cardiovasc Pharmacol 28:533–539. 41. Hinderling PH, Garrett ER, Wester RD. 1977. Pharmacokinetics of beta-methyldigoxin in healthy humans I: Intravenous studies. J Pharm Sci 66: 242–253. 42. Zilly W, Richter E, Rietbrock N. 1978. Pharmacokinetics of digoxin and methyldigoxin in patients with acute hepatitis. Med Klin 73:463–469. 43. Tsutsumi K, Nakashima H, Tateishi T, Imagawa M, Nakano S. 1993. Pharmacokinetics of betamethyldigoxin in subjects with normal and impaired renal function. J Clin Pharmacol 33:154– 160. 44. Kullak-Ublick GA, Ismair MG, Stieger B, Landmann L, Huber R, Pizzagalli F, Fattinger K, Meier PJ, Hagenbuch B. 2001. Organic anion-transporting polypeptide B (OATP-B) and its functional comparison with three other OATPs of human liver. Gastroenterology 120:525–533. 45. Cui Y, Konig J, Nies AT, Pfannschmidt M, Hergt M, Franke WW, Alt W, Moll R, Keppler D. 2003. Detection of the human organic anion transporters SLC21A6 (OATP2) and SLC21A8 (OATP8) in liver and hepatocellular carcinoma. Lab Invest 83:527– 538. 46. Latini R, Tognoni G, Kates RE. 1984. Clinical pharmacokinetics of amiodarone. Clin Pharmacokinet 9:136–156. 47. Veronese ME, McLean S, Hendriks R. 1988. Plasma protein binding of amiodarone in a patient population: Measurement by erythrocyte partitioning and a novel glass-binding method. Br J Clin Pharmacol 26:721–731. 48. Jun AS, Brocks DR. 2001. High-performance liquid chromatography assay of amiodarone in rat plasma. J Pharm Pharm Sci 4:263–268.
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
Department of Pharmaceutics and Therapeutics, Programs for Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan 2
Department of Pharmacy, Chugoku Rousai Hospital, 1-5-1 Hiro-Tagaya, Kure City, Hiroshima 737-0193, Japan
Received 29 October 2004; revised 8 February 2005; accepted 11 February 2005 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jps.20346
ABSTRACT: Recently, we found that potent P-glycoprotein (P-gp) inhibitors, such as verapamil and cyclosporin A, markedly modulated the pharmacokinetics of digoxin in rats, whereas they did not affect b-methyldigoxin pharmacokinetics significantly. Digoxin is also a substrate of rat organic anion transporting polypeptide 2 (Oatp2). Here, we compared the magnitude of Oatp2-mediated drug interaction of digoxin and bmethyldigoxin using amiodarone as an Oatp2 inhibitor in rats. Amiodarone (20 mg/kg) given intravenously significantly increased plasma levels and decreased biliary excretion, liver distribution, and intestinal distribution of digoxin administered intravenously at a dose of 10 mg/kg. Amiodarone also significantly decreased biliary excretion and liver distribution of b-methyldigoxin, but the change in plasma levels of b-methyldigoxin was quite small. These findings may give a clue in selecting these cardiac glycosides in clinical pharmacotherapy for patients receiving multiple drugs towards escape from Oatp2mediated drug interactions. ß 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1196–1203, 2005
Keywords: organic anion-transporting polypeptide 2 (Oatp2); digoxin; b-methyldigoxin; drug interaction; amiodarone
INTRODUCTION Since the discovery of digitalis glycosides or extracts of the common foxglove plant (Digitalis purourea) as medicine in 1775 by Scottish doctor William Withering, digoxin has been widely used in cardiology as the safe inotropic drug.1–3 Derivatives of digoxin, such as a-methyldigoxin, bmethyldigoxin, and b-acetyldigoxin, have been developed to increase the intestinal absorption of digoxin. These derivatives have the same mechanism of action and potencies with digoxin, but have significantly higher oral bioavailabilities
Correspondence to: Mikihisa Takano (Telephone: 81-82257-5315; Fax: 81-82-257-5319; E-mail: [email protected]) Journal of Pharmaceutical Sciences, Vol. 94, 1196–1203 (2005) ß 2005 Wiley-Liss, Inc. and the American Pharmacists Association
1196
than digoxin in humans. Both digoxin and bmethyldigoxin are commonly prescribed in Japan in the treatment of congestive heart failure and other congestive states. The recommended maintenance doses of oral digoxin and b-methyldigoxin are, respectively, 0.125–0.5 and 0.05– 0.2 mg/day, which are depending on their oral bioavailabilities.4,5 Many compounds induce drug interactions when coadministered with digoxin clinically.6 Digoxin is a substrate of P-glycoprotein (P-gp) and the drug interactions of digoxin with various compounds, such as quinidine, verapamil, nifedipine, and rifampicin, are now explained by P-gp-mediated drug interaction.7–10 P-gp, an ATP-dependent efflux pump, is expressed in various normal human and rodent tissues, including the intestine, liver, kidney, adrenal gland, brain, eye, and testis.11,12 In these tissues, P-gp
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
OATP2-MEDIATED DRUG INTERACTION
limits the entry and/or accumulation of endogenous and exogenous P-gp substrates such as steroid hormones, anticancer agents, immunosuppressive agents, calcium channel blockers, b-blockers, and so on.13,14 In contrast, the involvement of P-gp in b-methyldigoxin pharmacokinetics was unclear, although other cardiac glycosides, such as digitoxin, a-methyldigoxin, and b-acetyldigoxin, are reportedly P-gp substrates.15 In the previous report, we compared the magnitudes of P-gp-mediated drug interaction of digoxin and bmethyldigoxin pharmacokinetically using wellknown P-gp inhibitors, verapamil and cyclosporin A, in rats. In that study, we found that P-gpmediated drug interactions can easily occur in digoxin, but hardly in b-methyldigoxin.16 In addition to P-gp, digoxin is also known as a substrate of rat organic anion transporting polypeptide 2 (Oatp2).17–19 Oatp2 has a broad substrate specificity and accepts various organic anions and cations, in addition to cardiac glycosides such as digoxin and ouabain. Oatp2 is predominantly expressed at the sinusoidal membrane in perivenous hepatocytes, and in the brain and retina to some extent.19–22 Some Oatp2related compounds, such as indomethacin and amiodarone, also cause drug interactions with digoxin in humans.23–26 The interaction of digoxin with indomethacin has been found in infants, elderly, or patients with renal failure, which resulted in a significant elevation of serum digoxin levels.25–27 The interaction with amiodarone has been observed even in normal subjects under usual dosage regimen, in which renal and nonrenal clearances of digoxin are reduced significantly.23,24,28–30 In the interaction of digoxin with indomethacin, however, the contribution of Oatp2-mediated interaction may be small, if any, because the inhibitory potency of indomethacine on Oatp2-mediated digoxin transport is weak (>100 mM). In addition, the plasma unbound concentration of indomethacin is low, because of high plasma protein binding (>96%).18 On the other hand, amiodarone is a potent Oatp2 inhibitor with a Ki value of 1.8 mM, as estimated by digoxin uptake in Xenopus oocytes.31 Amiodarone is also known as a P-gp inhibitor and its Ki value for human P-gp is reportedly 45.6 mM, which was estimated from digoxin transport study in MDR1expressing LLC-PK1 cells.32 It is reported that amiodarone inhibits the uptake of digoxin into hepatocytes and increases its blood levels in rats.24 Regarding the interaction between digoxin and amiodarone, Kodawara et al. reported that Oatp2
1197
rather than P-gp may be one of the interaction sites, based on in vitro transport study using P-gpexpressing LLC-GA5-COL 150 cell monolayers and Oatp2-expressing Xenopus oocytes.31 In the present study, we compared the magnitudes of Oatp2-mediated drug interaction of digoxin and b-methyldigoxin pharmacokinetically by using amiodarone as an Oatp2 inhibitor in rats. The involvement of Oatp2 in b-methyldigoxin pharmacokinetics is unclear so far. Present study is expected to give a clue in selecting cardiac glycosides in clinical pharmacotherapy towards escape from P-gp- and/or Oatp2-mediated drug interactions.
MATERIALS AND METHODS Materials Digoxin was obtained from Sigma-Aldrich Company/Japan (Tokyo, Japan). b-Methyldigoxin was a gift from Nippon Roche (Kanagawa, Japan). Amiodarone was purchased from Sigma-Aldrich Company/Japan. Dulbecco’s-phosphate buffered saline (D-PBS) was from Gibco Laboratories (Life Technologies, Inc., NY). All other chemicals used were of the highest purity available. Animals Male Wistar rats weighing 220–300 g (8–9 weeks old) were fasted overnight with free access to water before the experiments. Animal experiments were performed in accordance with the Guide for Animal Experimentation from the Committee of Research Facilities for Laboratory Animal Sciences, Graduate School of Biomedical Sciences, Hiroshima University. In Vivo Pharmacokinetics Rats were fasted overnight, anesthetized with pentobarbital (30 mg/kg intraperitoneal injection), and affixed supine on a surface kept at 378C. In vivo pharmacokinetic studies of cardiac glycosides were performed in a similar manner as reported previously.16 Briefly, cannulation was made with polyethylene tubing (PE-50) at a femoral vein and a femoral artery, respectively. The urinary bladder and bile duct were also cannulated with polyethylene tubing PE-50 and PE-10, respectively. Digoxin and b-methyldigoxin were dissolved in pH 7.4 phosphate buffer containing 5% ethanol at a concentration of 5 mg/ml, JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
1198
FUNAKOSHI ET AL.
and the solution was administered by bolus injection via the cannula inserted at the femoral vein at a dose of 10 mg/kg. Blood was collected via the cannula inserted at the femoral artery at 5, 10, 30, 60, 120, 180, and 240 min after administration of a cardiac glycoside. Bile was collected serially via the cannula at 60, 120, and 240 min after administration. Urine was collected continuously via the cannula for 240 min. In inhibition study, amiodarone was dissolved in 30% ethanol-aqueous solution at a concentration of 5 mg/ml, and the solution was injected intravenously via the cannula 10 min prior to the administration of a cardiac glycoside. The dose of amiodarone was 5 or 20 mg/kg. Sampling of blood, bile, and urine was carried out in the same time schedules as described above. Plasma was separated from blood by centrifugation to determine plasma concentration of a cardiac glycoside. The area under the plasma concentration-time curves (AUC) was estimated by a trapezoidal rule using plasma levels of a drug until 240 min (AUC0–240), and in vivo total plasma clearance (CLtotal) was calculated by dividing the intravenous dose by AUC0–240 of a drug. In Vivo Tissue Distribution Separately, tissue distribution of two cardiac glycosides was determined in untreated control and amiodarone-treated, anesthetized rats. In case of inhibition study, rats received amiodarone (20 mg/kg) intravenously at first, then a cardiac glycoside (10 mg/kg) intravenously from the tail vein. Rats were exsanguined by decaptation to isolate the liver, heart, lung, and/or intestine 30 min after injection of a cardiac glycoside. Blood was also collected at the same time. Isolated tissue was homogenized with a three- to ninefold volume of distilled water, and the homogenate was centrifuged at 3000 rpm for 10 min to obtain the supernatant. Blood was centrifuged at 3000 rpm for 10 min to obtain plasma sample. The tissue distribution of a cardiac glycoside was expressed as the ratio of concentration in the tissue against that in plasma (T/P ratio). Analysis Concentrations of digoxin and b-methyldigoxin in biological fluids (plasma, bile, urine, supernatant of tissue homogenate) were determined by a fluorescence polarization immunoassay (FPIA, TDX1, Dainabot Co., Ltd., Tokyo, Japan) after JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
diluting the sample appropriately to a concentration range from 0.2 to 4.0 ng/ml. Values were expressed as the mean SE. Treatment groups were compared by two-tailed Student’s t-test for unpaired samples. A p-value of less than 0.05 was considered statistically significant.
RESULTS Effect of Amiodarone on Pharmacokinetics of Digoxin and b-Methyldigoxin Amiodarone at a dose of 20 mg/kg significantly increased plasma levels of digoxin given intravenously, whereas amiodarone at a dose of 5 mg/kg did not show any significant effect (Figure 1A). In contrast, the effect of amiodarone on plasma levels of b-methyldigoxin was observed only in initial 10 min even at a dose of 20 mg/kg (Figure 1B). In Table 1, AUC0–240 and CLtotal of these cardiac glycosides in untreated control and amiodarone-treated rats were summarized. Amiodarone (20 mg/kg) increased the AUC0–240 of digoxin by more than twofold, whereas it did not affect AUC0–240 of b-methyldigoxin significantly. Effect of amiodarone on biliary excretion of digoxin and b-methyldigoxin is shown in Figure 2. The biliary excretion of these cardiac glycosides during 4 h after intravenous administration was almost the same extents in untreated control rats. On one hand, the initial excretion rate of digoxin was approximately 1.8-fold higher than that of bmethyldigoxin, suggesting some difference in the liver uptake rate between them. Treatment with amiodarone decreased the biliary excretion of both digoxin and b-methyldigoxin in a dose-dependent manner. At 4 h after administration, amiodarone (20 mg/kg) inhibited the cumulative biliary excretion of digoxin by 54% and that of b-methyldigoxin by 77%. The effect of amiodarone on urinary excretion of digoxin and b-methyldigoxin is shown in Figure 3. Amiodarone (20 mg/kg) significantly inhibited the urinary excretion of digoxin, though the urinary excretion of digoxin was quite small in rats. Amiodarone did not affect the urinary excretion of b-methyldigoxin significantly. Effect of Amiodarone on Tissue Distribution of Digoxin and b-Methyldigoxin The effect of amiodarone (20 mg/kg) on tissue distribution of cardiac glycosides was evaluated in
OATP2-MEDIATED DRUG INTERACTION
1199
Figure 1. Plasma concentration-time profiles of digoxin and b-methyldigoxin given intravenously at a dose of 10 mg/kg in untreated control (*), amiodarone (5 mg/kg)treated (~), and amiodarone (20 mg/kg)-treated (*) rats. Amiodarone was administered intravenously 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). *Significantly different between the untreated control and amiodarone (20 mg/kg)-treated rats at a level of p < 0.05.
the liver, lung, kidney, and intestine (Table 2). In untreated control rats, both cardiac glycosides distributed to the liver preferentially. Digoxin also distributed to the intestine at a higher extent as compared with those to the heart and lung. bMethyldigoxin evenly distributed to the lung, heart, and intestine. Amiodarone significantly decreased the liver distribution of both cardiac glycosides to approximately 20–30% of control. Also, amiodarone decreased the intestinal distribution of digoxin by approximately 60%, but not of b-methyldigoxin.
DISCUSSION The pharmacokinetics of digoxin is known to be susceptible to many commonly prescribed drugs including antipyretic/analgesic agents, anti-arrhythmic agents, calcium channel blockers, steroid hormones, immunosuppressants, chemotherapeutic drugs, antibiotics, proton pump inhibitors, and so on.33–35 Most of these interactions with digoxin are explained by P-gpmediated drug interactions. In clinical therapy, such drug interactions with digoxin often occur in
Table 1. AUC0–4 and CLtotal, 0–4 of Digoxin and b-Methyldigoxin After Intravenous Administration at a Dose of 10 mg/kg in Untreated Control and Amiodarone-Treated Rats AUC0–4 (ng min/mL) Digoxin þAmiodarone (5 mg/kg) þAmiodarone (20 mg/kg) b-Methyldigoxin þAmiodarone (5 mg/kg) þAmiodarone (20 mg/kg)
304.0 32.6 397.2 84.6 730.0 11.3* 1016 80 1230 14 1254 207
CLtotal,
0–4
(mL/min/kg)
35.7 4.4 26.5 6.4 14.1 2.4* 10.1 0.9 8.1 0.1 8.2 1.5
Amiodarone was administered intravenously at a dose of 5 or 20 mg/kg 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). *Significantly different from digoxin alone at a level of p < 0.05. JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
1200
FUNAKOSHI ET AL.
Figure 2. Biliary excretion-time profiles of digoxin and b-methyldigoxin given intravenously at a dose of 10 mg/kg in untreated control (*), amiodarone (5 mg/kg)treated (~), and amiodarone (20 mg/kg)-treated (*) rats. Amiodarone was administered intravenously 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). *Significantly different between the untreated control and amiodarone (20 mg/kg)-treated rats at a level of p < 0.05.
the elderly, in neonates, and in patients with renal dysfunction. It is important to clarify the molecular mechanisms of such drug interactions in order to predict and avoid the interactions. In contrast to digoxin, information on b-methyldigoxin is quite limited. Previously, we compared the magnitude of P-gp-mediated drug interaction of digoxin and b-methyldigoxin using potent P-gp
inhibitors, verapamil and cyclosporin A.16 In that study, P-gp-mediated drug interactions occurred easily in digoxin, but hardly in b-methyldigoxin. Digoxin is also known as a substrate of Oatp2, or human OATP8, and possibly of Oatp3,36,37 though it is unknown whether b-methyldigoxin is also recognized as a substrate by Oatp2. Here, we compared the possible Oatp2-mediated drug
Figure 3. Urinary excretion of digoxin and b-methyldigoxin during 4 h after intravenous administration at a dose of 10 mg/kg in untreated control (&), amiodarone (5 mg/kg)-treated ( ), and amiodarone (20 mg/kg)-treated (&) rats. Amiodarone (AMD) was administered intravenously 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3–7). JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
OATP2-MEDIATED DRUG INTERACTION
1201
Table 2. Effect of Amiodarone on Tissue Distribution (Tissue-To-Plasma Concentration Ratio) of Digoxin and b-Methyldigoxin in Rats
Digoxin þAmiodarone (20 mg/kg) b-Methyldigoxin þAmiodarone (20 mg/kg)
Liver
Lung
Heart
Intestine
14.7 6.8 4.5 0.8* 10.5 1.6 2.6 0.8*
2.10 0.12 1.76 0.09 1.60 0.17 1.32 0.13
2.46 0.06 2.76 0.34 1.83 0.31 1.53 0.18
5.86 0.78 2.22 0.20* 1.55 0.50 1.25 0.24
Amiodarone was administered intravenously at a dose of 20 mg/kg 10 min prior to the administration of a cardiac glycoside. Values are expressed as the mean SE (n ¼ 3). *Significantly different from digoxin alone at a level of p < 0.05.
interaction of digoxin and b-methyldigoxin pharmacokinetically, using amiodarone as an Oatp2 inhibitor in rats. Amiodarone is a Class III antiarrhythmic agent, and its clinical use is generally restricted to the treatment of drug-resistant arrhythmias because of serious adverse effects. Amiodarone is also known to cause drug interactions with various drugs including digoxin, warfarin, procainamide, lidocaine, cyclosporin, quinidine, and so on.23,24,28–30,38 –40 Regarding the interaction between digoxin and amiodarone, Kodawara et al. recently proposed the Oatp2-mediated drug interaction, rather than P-gp-mediated, based on in vitro studies as described in the Introduction section.31 In good agreement with their report, amiodarone (20 mg/kg, i.v.) decreased the distribution of digoxin and b-methyldigoxin to the liver, where Oatp2 is expressed (Figure 2 and Table 2). The decrease in liver distribution and consequent biliary excretion of these cardiac glycosides would be probably due to the Oatp2-mediated drug interaction, because P-gp-mediated drug interaction in b-methyldigoxin pharmacokinetics can be ruled out as reported previously.16 In the present study, a marked difference was observed in the effect of amiodarone on plasma levels between digoxin and b-methyldigoxin. Amiodarone (20 mg/kg) significantly increased plasma AUC0–4 of digoxin by 2.4-fold of control, whereas the effect on plasma AUC0–4 of bmethyldigoxin was quite small (1.2-fold) (Table 1). It is difficult to explain the discrepancy between the effects of amiodarone on the liver distribution and the plasma level of these cardiac glycosides. The lower tissue distribution of b-methyldigoxin than digoxin in the early stage (distribution phase) (Figure 1 and Table 2) may be related to the lesser effect of reduced biliary excretion on plasma bmethyldigoxin level, at least partly. Further study is necessary to clarify the different effects of
amiodarone on plasma profiles of digoxin and bmethyldigoxin. As described in the Introduction section, the interaction of digoxin with amiodarone has been observed frequently in humans.23,24,28–30 On one hand, there is a species difference in elimination pathways of digoxin and b-methyldigoxin between rats and humans. For example, more than 30% of dose of these cardiac glycosides is recovered in urine within 24 h in humans.41–43 Thus, there may be some differences in the extent of hepatic distribution of these cardiac glycosides between rats and humans, although digoxin is recognized by human OATP8 (SLC21A8) and OATP8 is localized to the sinusoidal membrane of hepatocytes in humans, as well as in rats.44,45 In addition, the protein binding of amiodarone is very high (more than 96% or more than 99.9% in average, depending on literatures),46,47 indicating that the concentration of unbound amiodarone is very low in plasma. The maximal plasma concentration of amiodarone given intravenously at a dose of 20 mg/ kg would be less than 15 mM, though the plasma level would be kept for very long time, according to the literatures.46–48 Thus, there is a difference between the reported Ki value (1.8 mM) of amiodarone on Oatp2 and possible unbound concentration of amiodarone in the present study. It may be due to the extensive tissue distribution of amiodarone, which inhibits the transporter more potently than expected based on its unbound plasma concentration. To explain the interaction mechanism(s) between cardiac glycosides and amiodarone completely, further studies, including other pharmacokinetic interactions than Oatp2mediated transport, would be necessary by taking the above points into consideration. In conclusion, we compared the magnitude of Oatp2-mediated drug interaction of digoxin and b-methyldigoxin in rats. Amiodarone, a potent Oatp2 inhibitor, decreased the distribution of JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
1202
FUNAKOSHI ET AL.
these cardiac glycosides to the liver and their biliary excretions. On the other hand, amiodarone modified plasma levels of digoxin significantly, but not of b-methyldigoxin. Collectively, the present and our previous findings16 may give a clue in selecting these cardiac glycosides in clinical pharmacotherapy for patients taking multiple drugs, towards escape from P-gp- and/or Oatp2-mediated drug interactions.
14.
REFERENCES
16.
1. Friend DG. 1976. Digitalis after two centuries (William Withering). Arch Surg 111:14–19. 2. Hauptman PJ, Kelly RA. 1999. Digitalis. Circulation 99:1265–1270. 3. Kjeldsen K, Bundgaard H. 2003. Myocardial Na,KATPase and digoxin therapy in human heart failure. Ann NY Acad Sci 986:702–707. 4. Ito Y, Seki K, Kimura E. 1975. Multiclinical open studies on the effect of beta-methyldigoxin on congestive heart failure with atrial fibrillation. Jpn Heart J 16:538–547. 5. Das G. 1989 Beta-methyl digoxin: A better absorbable digoxin. Int J Clin Pharmacol Ther Toxicol 27: 521–525. 6. Marcus FI. 1985. Pharmacokinetic interactions between digoxin and other drugs. J Am Coll Cardiol 5:82–90. 7. De Lannoy IA, Silverman M. 1992. The MDR1 gene product, P-glycoprotein, mediates the transport of the cardiac glycoside, digoxin. Biochem Biophys Res Commun 189:551–557. 8. Fromm MF, Kim RB, Stein CM, Wilkinson GR, Roden DM. 1999. Inhibition of P-glycoproteinmediated drug transport: A unifying mechanism to explain the interaction between digoxin and quinidine. Circulation 99:552–557. 9. Verschraagen M, Koks CH, Schellens JH, Beijnen JH. 1999. P-glycoprotein system as a determinant of drug interactions: The case of digoxin-verapamil. Pharmacol Res 40:301–306. 10. Greiner B, Eichelbaum M, Fritz P, Kreichgauer H-P, von Richter O, Zundler J, Kroemer HK. 1999. The role of intestinal P-glycoprotein in the interaction of digoxin and rifampin. J Clin Invest 104:147– 153. 11. Thiebaut F, Tsuruo T, Hamada H, Gottesman MM, Pastan I, Willingham MC. 1987. Cellular localization of the multidrug-resistance gene product P-glycoprotein in normal human tissues. Proc Natl Acad Sci USA 84:7735–7738. 12. Holash JA, Stewart PA. 1993. The relationship of astrocyte-like cells to the vessels that contribute to the blood-ocular barriers. Brain Res 629:218–224. 13. Hunter J, Jepson MA, Tsuruo T, Simmons NL, Hirst BH. 1993. Functional expression of P-glyco-
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005
15.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
protein in apical membranes of human intestinal Caco-2 cells. Kinetics of vinblastine secretion and interaction with inhibitors. J Biol Chem 268: 14991–14997. Tsuji A, Tamai I. 1996. Carrier-mediated intestinal transport of drugs. Pharm Res 13:963–977. Pauli-Magnus C, Mu¨rdter T, Godel A, Mettang T, Eichelbaum M, Klotz U, Fromm MF. 2001. P-glycoprotein-mediated transport of digitoxin, a-methyldigoxin and b-acetyldigoxin. NaunynSchmiedeberg’s Arch Pharmacol 363:337–343. Funakoshi S, Murakami T, Yumoto R, Kiribayashi Y, Takano M. 2003. Role of P-glycoprotein in pharmacokinetics and drug interactions of digoxin and beta-methyldigoxin in rats. J Pharm Sci 92: 1455–1463. Noe B, Hagenbuch B, Stieger B, Meier PJ. 1997. Isolation of a multispecific organic anion and cardiac glycoside transporter from rat brain. Proc Natl Acad Sci USA 94:10346–10350. Shitara Y, Sugiyama D, Kusuhara H, Kato Y, Abe T, Meier PJ, Itoh T, Sugiyama Y. 2002. Comparative inhibitory effects of different compounds on rat oatpl (slc21a1)- and Oatp2 (Slc21a5)-mediated transport. Pharm Res 19:147–153. Sugiyama D, Kusuhara H, Shitara Y, Abe T, Sugiyama Y. 2002. Effect of 17 beta-estradiolD-17 beta-glucuronide on the rat organic anion transporting polypeptide 2-mediated transport differs depending on substrates. Drug Metab Dispos 30:220–223. Gao B, Stieger B, Noe B, Fritschy JM, Meier PJ. 1999. Localization of the organic anion transporting polypeptide 2 (Oatp2) in capillary endothelium and choroid plexus epithelium of rat brain. J Histochem Cytochem 47:1255–1264. Gao B, Wenzel A, Grimm C, Vavricka SR, Benke D, Meier PJ, Reme CE. 2002. Localization of organic anion transport protein 2 in the apical region of rat retinal pigment epithelium. Invest Ophthalmol Vis Sci 43:510–514. van Montfoort JE, Schmid TE, Adler ID, Meier PJ, Hagenbuch B. 2002. Functional characterization of the mouse organic-anion-transporting polypeptide 2. Biochim Biophys Acta 1564:183–188. Oetgen WJ, Sobol SM, Tri TB, Heydorn WH, Rakita L. 1984. Amiodarone-digoxin interaction. Clinical and experimental observations. Chest 86:75–79. Lambert C, Lamontagne D, Hottlet H, du Souich P. 1989. Amiodarone-digoxin interaction in rats. A reduction in hepatic uptake. Drug Metab Dispos 17:704–708. Jorgensen HS, Christensen HR, Kampmann JP. 1991. Interaction between digoxin and indomethacin or ibuprofen. Br J Clin Pharmacol 31:108– 110. Haig GM, Brookfield EG. 1992. Increase in serum digoxin concentrations after indomethacin therapy
OATP2-MEDIATED DRUG INTERACTION
27.
28.
29. 30.
31.
32.
33.
34.
35.
36.
37.
in a full-term neonate. Pharmacotherapy 12:334– 336. Johnson AG, Seidemann P, Day RO. 1994. NSAIDrelated adverse drug interactions with clinical relevance. An update. Int J Clin Pharmacol Ther 32:509–532. Fenster PE, White NW, Jr., Hanson CD. 1985. Pharmacokinetic evaluation of the digoxin-amiodarone interaction. J Am Coll Cardiol 5:108–112. Lesko LJ. 1989. Pharmacokinetic drug interactions with amiodarone. Clin Pharmacokinet 17:130–140. Freitag D, Bebee R, Sunderland B. 1995. Digoxinquinidine and digoxin-amiodarone interactions: Frequency of occurrence and monitoring in Australian repatriation hospitals. J Clin Pharm Ther 20:179–183. Kodawara T, Masuda S, Wakasugi H, Uwai Y, Futami T, Saito H, Abe T, Inu K. 2002. Organic anion transporter oatp2-mediated interaction between digoxin and amiodarone in the rat liver. Pharm Res 19:738–743. Katoh M, Nakajima M, Yamazaki H, Yokoi T. 2001. Inhibitory effects of CYP3A4 substrates and their metabolites on P-glycoprotein-mediated transport. Eur J Pharm Sci 12:505–513. Davis TD, Vanderveen RL, Nienhuis M. 1983. Digoxin. In: Mungall DR, editor. Applied clinical pharmacokinetics. New York: Raven Press. pp 79– 102. Rodin SM, Johnson BF. 1988. Pharmacokinetic interactions with digoxin. Clin Pharmacokinet 15: 227–244. Nolan PE, Jr., Raehl CL, Zarembski DG. 1996. Congestive heart failure. In: Herfindal ET, Gourley DR, editors. Textbook of therapeutics drug and disease management: Cardiovascular disorders. Section 10. 6th edition. Baltimore: Williams & Wilkins. pp 729–761. Cattori V, van Montfoort JE, Stieger B, Landmann L, Meijer DK, Winterhalter KH, Meier PJ, Hagenbuch B. 2001. Localization of organic anion transporting polypeptide 4 (Oatp4) in rat liver and comparison of its substrate specificity with Oatp1, Oatp2 and Oatp3. Pflugers Arch 443:188–195. Hagenbuch B, Meier PJ. 2003. The superfamily of organic anion transporting polypeptides. Biochim Biophys Acta 1609:1–18.
1203
38. Heimark LD, Wienkers L, Kunze K, Gibaldi M, Eddy AC, Trager WF, O’Reilly RA, Goulart DA. 1992. The mechanism of the interaction between amiodarone and warfarin in humans. Clin Pharmacol Ther 51:398–407. 39. Nicolau DP, Uber WE, Crumbley AJ 3rd, Strange C. 1992. Amiodarone-cyclosporine interaction in a heart transplant patient. J Heart Lung Transplant 11:564–568. 40. Ha HR, Candinas R, Stieger B, Meyer UA, Follath F. 1996. Interaction between amiodarone and lidocaine. J Cardiovasc Pharmacol 28:533–539. 41. Hinderling PH, Garrett ER, Wester RD. 1977. Pharmacokinetics of beta-methyldigoxin in healthy humans I: Intravenous studies. J Pharm Sci 66: 242–253. 42. Zilly W, Richter E, Rietbrock N. 1978. Pharmacokinetics of digoxin and methyldigoxin in patients with acute hepatitis. Med Klin 73:463–469. 43. Tsutsumi K, Nakashima H, Tateishi T, Imagawa M, Nakano S. 1993. Pharmacokinetics of betamethyldigoxin in subjects with normal and impaired renal function. J Clin Pharmacol 33:154– 160. 44. Kullak-Ublick GA, Ismair MG, Stieger B, Landmann L, Huber R, Pizzagalli F, Fattinger K, Meier PJ, Hagenbuch B. 2001. Organic anion-transporting polypeptide B (OATP-B) and its functional comparison with three other OATPs of human liver. Gastroenterology 120:525–533. 45. Cui Y, Konig J, Nies AT, Pfannschmidt M, Hergt M, Franke WW, Alt W, Moll R, Keppler D. 2003. Detection of the human organic anion transporters SLC21A6 (OATP2) and SLC21A8 (OATP8) in liver and hepatocellular carcinoma. Lab Invest 83:527– 538. 46. Latini R, Tognoni G, Kates RE. 1984. Clinical pharmacokinetics of amiodarone. Clin Pharmacokinet 9:136–156. 47. Veronese ME, McLean S, Hendriks R. 1988. Plasma protein binding of amiodarone in a patient population: Measurement by erythrocyte partitioning and a novel glass-binding method. Br J Clin Pharmacol 26:721–731. 48. Jun AS, Brocks DR. 2001. High-performance liquid chromatography assay of amiodarone in rat plasma. J Pharm Pharm Sci 4:263–268.
JOURNAL OF PHARMACEUTICAL SCIENCES, VOL. 94, NO. 6, JUNE 2005