Eur J Clin Pharmacol (1992) 42:463-464 European Journal of
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Letter to the editors
Verapamil and drug metabolism by the cytochrome P450 isoform CYP1A2 U. Fuhr 1, B. G. Woodcock 1, and M. Siewert 2 Department of Clinical Pharmacology, University Hospital, Frankfurt/M. and Central Laboratory of German Pharmacists,Eschborn, FRG Received: June 5,1991/Accepted in revised form: September 9, 1991
Key words: Verapamil, Cytochrome P450; theophylline, CYP1A2, drug interaction
A decrease in the clearance of theophylline when verapamil is co-administered [1] is a clinically relevant drug interaction involving hepatic cytochrome P450 isoforms [2]. Evidence obtained from mammalian cells genetically engineered to express a single cytochrome P450 isoform has shown that CYPIA2 is responsible for a major part of theophylline metabolism in man [Fuhr et al. unpublished observation]. Investigations have now been done in vitro to establish whether verapamil is an inhibitor of and a substrate for CYPIA2.
Verapamil as an inhibitor of CYP1A2 The effect of 500 gM verapamil on 3-demethylation of caffeine (500 gM), a specific probe for CYPIA2 activity [3], was determined using duplicate incubations with liver microsomes from 4 human donors in the presence of N A D R at 37°C (15 min), as previously described [4]. Verapamil reduced caffeine 3-demethylation to 65 (9) % of the control [mean with (SD); Fig. i a].
was found, but only 4 data points were available for analysis. The 35% inhibition of caffeine 3-demethylation by verapamil clearly indicates that verapamil binds to CYP1A2, since no other isoenzyme is expected to contribute significantly to the 3-demethylation of caffeine under
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Liver microsomes from 4 human donors were incubated with verapamil (500 gM), with and without furafylline (100 gM), a selective and potent inhibitor of CYPIA2 [5]. It was found using HPLC that furafylline slightly reduced the formation rate of norverapamil, one of several major metabolites of verapamil after oral administration, which is present in plasma at a higher concentration than that of the parent drug. In all four microsome samples it was reduced [to 90 (4) % of that without inhibitor; Fig. lb]. No correlation between the rate of norverapamil formation and the rate of caffeine 3-demethylation in the samples
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DONOR A b DONOR B DONOR DONOR D Fig. la, b. Rates of caffeine 3-demethylation and norverapamil formation (each substrate 500 gM) in human liver microsomes from four donors in the absence and presence of inhibitors (verapamil, 500 ~tM; furafylline, 100 gM). a caffeine 3-demethylation [ ] caffeine without inhibitor [ ] caffeine plus verapamil, b norverapamil formation [ ] verapamiI without inhibitor [ ] verapamil plus furafylline
464 the in vitro conditions chosen [3, 4]. The extent of the in vitro inhibition of caffeine demethylation, and the magnitude of the in vivo interaction between verapamil and theophylline, parallels the inhibitory effect of certain quinolone antibiotics on theophylline metabolism in vivo, and on the activity of CYP1A2 in vitro [4]. The influence of verapamil on caffeine 3-demethylation was similar to that on all three primary metabolic pathways of theophylline found using h u m a n liver microsomes [2]. The small decrease in the rate of formation of norverapamil, one of the main verapamil metabolites, produced by furafylline indicates that C Y P I A 2 has only a minor role in this metabolic pathway. This is consistent with recent work by K r o e m e r et al. [6], showing that two-thirds of norverapamil formation is mediated by CYP3A4 at similar, high concentrations of verapamil in vitro. In this regard, it was noted that the norverapamil concentrations produced were considerable (about 20% of the parent compound), and further degradation of this metabolite may have occurred during the incubation. The data suggest that verapamil is an inhibitor, but not a substrate of CYP1A2 to an extent that is likely to reach clinical relevance. Thus, an interaction at this isoform m a y be responsible at least in part for the interaction between verapamil and theophylline described in vivo. The investigation did not permit a quantitative estim a t e of the extent to which verapamil inhibition of CYP1A2 reduces drug metabolism in vivo by this isoform. However, co-administration of verapamil with drugs metabolized by CYP1A2, e.g. theophylline, caffeine, phe-
nacetin and lidocaine, may give rise to or at least contribute to an interaction, and such a finding should not be unexpected. References
1. Nielsen-Kudsk JE, Buhl JS, Johannessen AC (1990) Verapamilinduced inhibition of theophylline in healthy humans. Pharmacol Toxico166:101-103 2. Robson RA, Miners JO, Matthews AR Stupans I, Meller D, McManus M, Birkett DJ (1988) Characterisation of theophylline metabolism by human liver microsomes. Inhibition and immunochemical studies. Biochem Pharmaco137:1651-1659 3. Butler MA, Iwasaki M, Guengerich FP, Kadlubar FK (1989) Human cytochrome P450pA (P-450IA2), the phenacetin O-deethylase, is primary responsible for the hepatic 3-demethylation of caffeine and N-oxidation of carcinogenic arylamines. Proc Natl Acad Sci USA 86:7696-7700 4. Fuhr U, Wolff T, Harder S, Schymanski R Staib AH (1990) Quinolone inhibition of cytochrome P-450-dependent caffeine metabolism in human liver microsomes. Drug Metabol Dispos 18: 10051010 5. Sesardic D, Boobis AR, Murray BR Murray S, Segura J, de la Torre R, Davies D S (1990) Furafylline is a potent and selective inhibitor of cytochrome P450IA2 in man. Br J Clin Pharmacol 29: 651~63 6. Kroemer HK, Beaune R Henderson CJ, Wolf CR, Heidemann H (1991) Identification of cytochrome P-450 isozymes involved in the metabolism of verapamil. Arch Pharmaco1343 [Suppl]: R124 Dr. U. Fuhr Abteilung Klinische Pharmakologie Universit~itsklinik Frankfurt Theodor-Stern-Kai 7 W-6000 Frankfurt am Main, FRG
Announcements The Biology and Pharmacotherapy of Manic-Depressive Disorders: Form Molecular Theories to Clinical Practice. A Satellite Symposium Affiliated to the XVHI th C. I. N. P: Congress
June 24-26, 1992 Copenhagen, Denmark
Information: Organizing Commitee (Arne Geisler and Arne MCrk) Department of Pharmacology University of Copenhagen 20 Juliane Maries Vej DK-2100 Copenhagen, Denmark Tel.: (45) 3 53-703 75 Fax: (45) 3 53-772 89 Satellite Symposium of the IXth International Congress of Endocrinology "Melatonin and the Pineal Gland: From Basic Science to Clinical Application"
September 6.9, 1992 Paris, France
Information: Scientific Secretary Prof. Y. Touitou Department of Biochemistry Faculty of Medicine Piti6-S alp6tribre 91 boulevard de l'H6pital F-75013 Paris, France
Fourth International Symposium on Disposition and Delivery of Peptide Drugs
April 23-25, 1993 The Netherlands
Information: Symposium Secretariat Center for Bio-Pharmaceutical Sciences E O. Box 9502 NL-2300 RA Leiden The Netherlands Tel.: (31) 712-7 43 41 Fax: (31) 712-742 77 XII th International Congress of Pharmacology
July 24-30, 1994 Montreal, Canada
Information: Congress Secretariat IUPHAR'94 Conference Services National Research Council Canada Ottawa, ON, Canada KIA OR6 Tel.: (613)993-9009 Fax: (613) 9 57-98 28
(~[~[~(~(~
e @Q erle@ g
@ Springer-Verlag 1992
Letter to the editors
Verapamil and drug metabolism by the cytochrome P450 isoform CYP1A2 U. Fuhr 1, B. G. Woodcock 1, and M. Siewert 2 Department of Clinical Pharmacology, University Hospital, Frankfurt/M. and Central Laboratory of German Pharmacists,Eschborn, FRG Received: June 5,1991/Accepted in revised form: September 9, 1991
Key words: Verapamil, Cytochrome P450; theophylline, CYP1A2, drug interaction
A decrease in the clearance of theophylline when verapamil is co-administered [1] is a clinically relevant drug interaction involving hepatic cytochrome P450 isoforms [2]. Evidence obtained from mammalian cells genetically engineered to express a single cytochrome P450 isoform has shown that CYPIA2 is responsible for a major part of theophylline metabolism in man [Fuhr et al. unpublished observation]. Investigations have now been done in vitro to establish whether verapamil is an inhibitor of and a substrate for CYPIA2.
Verapamil as an inhibitor of CYP1A2 The effect of 500 gM verapamil on 3-demethylation of caffeine (500 gM), a specific probe for CYPIA2 activity [3], was determined using duplicate incubations with liver microsomes from 4 human donors in the presence of N A D R at 37°C (15 min), as previously described [4]. Verapamil reduced caffeine 3-demethylation to 65 (9) % of the control [mean with (SD); Fig. i a].
was found, but only 4 data points were available for analysis. The 35% inhibition of caffeine 3-demethylation by verapamil clearly indicates that verapamil binds to CYP1A2, since no other isoenzyme is expected to contribute significantly to the 3-demethylation of caffeine under
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DONOR D
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Verapamil as a substratc for CYP1A2
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Liver microsomes from 4 human donors were incubated with verapamil (500 gM), with and without furafylline (100 gM), a selective and potent inhibitor of CYPIA2 [5]. It was found using HPLC that furafylline slightly reduced the formation rate of norverapamil, one of several major metabolites of verapamil after oral administration, which is present in plasma at a higher concentration than that of the parent drug. In all four microsome samples it was reduced [to 90 (4) % of that without inhibitor; Fig. lb]. No correlation between the rate of norverapamil formation and the rate of caffeine 3-demethylation in the samples
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DONOR A b DONOR B DONOR DONOR D Fig. la, b. Rates of caffeine 3-demethylation and norverapamil formation (each substrate 500 gM) in human liver microsomes from four donors in the absence and presence of inhibitors (verapamil, 500 ~tM; furafylline, 100 gM). a caffeine 3-demethylation [ ] caffeine without inhibitor [ ] caffeine plus verapamil, b norverapamil formation [ ] verapamiI without inhibitor [ ] verapamil plus furafylline
464 the in vitro conditions chosen [3, 4]. The extent of the in vitro inhibition of caffeine demethylation, and the magnitude of the in vivo interaction between verapamil and theophylline, parallels the inhibitory effect of certain quinolone antibiotics on theophylline metabolism in vivo, and on the activity of CYP1A2 in vitro [4]. The influence of verapamil on caffeine 3-demethylation was similar to that on all three primary metabolic pathways of theophylline found using h u m a n liver microsomes [2]. The small decrease in the rate of formation of norverapamil, one of the main verapamil metabolites, produced by furafylline indicates that C Y P I A 2 has only a minor role in this metabolic pathway. This is consistent with recent work by K r o e m e r et al. [6], showing that two-thirds of norverapamil formation is mediated by CYP3A4 at similar, high concentrations of verapamil in vitro. In this regard, it was noted that the norverapamil concentrations produced were considerable (about 20% of the parent compound), and further degradation of this metabolite may have occurred during the incubation. The data suggest that verapamil is an inhibitor, but not a substrate of CYP1A2 to an extent that is likely to reach clinical relevance. Thus, an interaction at this isoform m a y be responsible at least in part for the interaction between verapamil and theophylline described in vivo. The investigation did not permit a quantitative estim a t e of the extent to which verapamil inhibition of CYP1A2 reduces drug metabolism in vivo by this isoform. However, co-administration of verapamil with drugs metabolized by CYP1A2, e.g. theophylline, caffeine, phe-
nacetin and lidocaine, may give rise to or at least contribute to an interaction, and such a finding should not be unexpected. References
1. Nielsen-Kudsk JE, Buhl JS, Johannessen AC (1990) Verapamilinduced inhibition of theophylline in healthy humans. Pharmacol Toxico166:101-103 2. Robson RA, Miners JO, Matthews AR Stupans I, Meller D, McManus M, Birkett DJ (1988) Characterisation of theophylline metabolism by human liver microsomes. Inhibition and immunochemical studies. Biochem Pharmaco137:1651-1659 3. Butler MA, Iwasaki M, Guengerich FP, Kadlubar FK (1989) Human cytochrome P450pA (P-450IA2), the phenacetin O-deethylase, is primary responsible for the hepatic 3-demethylation of caffeine and N-oxidation of carcinogenic arylamines. Proc Natl Acad Sci USA 86:7696-7700 4. Fuhr U, Wolff T, Harder S, Schymanski R Staib AH (1990) Quinolone inhibition of cytochrome P-450-dependent caffeine metabolism in human liver microsomes. Drug Metabol Dispos 18: 10051010 5. Sesardic D, Boobis AR, Murray BR Murray S, Segura J, de la Torre R, Davies D S (1990) Furafylline is a potent and selective inhibitor of cytochrome P450IA2 in man. Br J Clin Pharmacol 29: 651~63 6. Kroemer HK, Beaune R Henderson CJ, Wolf CR, Heidemann H (1991) Identification of cytochrome P-450 isozymes involved in the metabolism of verapamil. Arch Pharmaco1343 [Suppl]: R124 Dr. U. Fuhr Abteilung Klinische Pharmakologie Universit~itsklinik Frankfurt Theodor-Stern-Kai 7 W-6000 Frankfurt am Main, FRG
Announcements The Biology and Pharmacotherapy of Manic-Depressive Disorders: Form Molecular Theories to Clinical Practice. A Satellite Symposium Affiliated to the XVHI th C. I. N. P: Congress
June 24-26, 1992 Copenhagen, Denmark
Information: Organizing Commitee (Arne Geisler and Arne MCrk) Department of Pharmacology University of Copenhagen 20 Juliane Maries Vej DK-2100 Copenhagen, Denmark Tel.: (45) 3 53-703 75 Fax: (45) 3 53-772 89 Satellite Symposium of the IXth International Congress of Endocrinology "Melatonin and the Pineal Gland: From Basic Science to Clinical Application"
September 6.9, 1992 Paris, France
Information: Scientific Secretary Prof. Y. Touitou Department of Biochemistry Faculty of Medicine Piti6-S alp6tribre 91 boulevard de l'H6pital F-75013 Paris, France
Fourth International Symposium on Disposition and Delivery of Peptide Drugs
April 23-25, 1993 The Netherlands
Information: Symposium Secretariat Center for Bio-Pharmaceutical Sciences E O. Box 9502 NL-2300 RA Leiden The Netherlands Tel.: (31) 712-7 43 41 Fax: (31) 712-742 77 XII th International Congress of Pharmacology
July 24-30, 1994 Montreal, Canada
Information: Congress Secretariat IUPHAR'94 Conference Services National Research Council Canada Ottawa, ON, Canada KIA OR6 Tel.: (613)993-9009 Fax: (613) 9 57-98 28
