Cellular localization of CYP3A proteins in various tissues from
Quantitative prediction of CYP3A-mediated drug interactions.
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CLINICALPHAKMACOLOG¥ & 'I'HEIt2kPEUTICS P16 American Society J:br Clinical Pharmacology and Therapeutics ~Em~UARY 2003 PI-53 QUANTITATIVE PREDICTION OF CYP3A-MEDIATED DRUG INTERACTIONS. R. E. Kimura, MD~ Y. C. Chen, MD, V. A. Jiyamapa-Sherna, MS, M. A. Hamman, BS, S. D. Hall, PhD, R. E. Galinsky, PharmD, Rush Children's Hospital, Indiana Univer- sity, Purdue University, Chicago, IL. Drug-drug interactions are the fourth leading cause of death in hospitals. CYP3A enzymes participate in more than half of all drug metabolism pathways and are a common locus of drug interactions in human intestine and liver. In vitro data has many limitations in the prediction of clinically important drug interactions. A novel approach has been developed to predict human drug interactions with midazo- lam (MDZ) using blood sampled simultaneously from the aorta and hepatic vein in chronically catheterized, physiologically stable rats. In vivo estimates in rats of K M for MDZ were 2.9 ug/ml in the presence and 1.3 ug/ml in the absence of 0.6 ug/ml ketoconazole (KET) using the well-sfirred model. The corresponding estimate of in vivo KET inhibitory potency (Ks) relative to the systemic concentration was 0.48 ug/ml. The in vivo parameters estimated from rat studies and the literature values for KET dose (400 mg pox 4 d) and systemic concentrations (5 ug/ml) from human studies were used to predict the pharmacokinetics of MDZ and the extent of interaction in hmnans. Drug concentrations were determined by HPLC. These studies indi- cate that the in vivo K~ for KET calculated from rats can be used in a human simulation to predict the effects of KET on MDZ pharma- cokinetics in humans. Observed Predicted Control KET Control KET Cmax (ng/ml) 22-37 90 27 88 AUC (ug/ml rain) 3.9-7.8 62 6 74 tl/2 (h) 2.2-2.8 8.7 2.5 9.6 PI-54 DIFFERENTIAL INHIBITION OF CYP3A4 AND CYP3A5 BY VERAPAMIL. Y. Wang, PhD, D. R. Jones, PhD, S. D. Hall, PhD, Indiana University-Purdue University at Indianapolis, Indianapolis, IN. Substantial interindividual differences in CYP3A activity contrib- ute greatly to variation in oral bioavailability and systemic clearance of CYP3A substrates. We have recently shown that verapamil is a mechanism-based inhibitor of CYP3A4. The purpose of this study is to compare the effects of verapamil on CYP3A4 and CYP3A5 activities, and to determine if different CYP3A5 expression levels in the human liver microsomes alter the inhibitory potency of vera- pamil. Testosterone 6[3-hydroxylation was used as a marker of CYP3A activity. The possibility that verapamil forms metabolic intermediate complex (MIC) with CYP3A was assessed using dual beam spectrophotometry. Verapamil was found to inhibit recombi- nant CYP3A4 activity in a time-dependent manner but have little effect on recombinant CYP3A5 activity. Verapamil formed MIC with recombinant CYP3A4 (53% of total cytochrome P450) but not with recombinant CYP3A5 as indicated by the appearance of the charac- teristic peak at 455nm. When human liver microsomes were prein- cubated with verapamil for 20 minutes, CYP3A activities of those that contained CYP3A5 in addition to CYP3A4 were reduced by only 20 to 40%, whereas the activities of those that contained only CYP3A4 were reduced by 70%. These findings indicate that the presence of variable CYP3A5/CYP3A4 enzyme expression in the liver may contribute to the interindividual variability associated with verapamil mediated drug interactions. PI-55 DROPERIDOL IS PREDOMINANTLY METABOLIZED BY HUMAN CYP3A ENZYMES. G.L. Lemma, MD, Z. Desta, PhD, D. R. Jones, PhD, J. C. Gorski, PhD, S. D. Hall, PhD, Indiana University School of Medicine, Indianapolis, IN. Droperidol (DRP) is an antipsychotic drug that prolongs the QTc interval and is used commonly to manage postoperative nausea and vomiting. Metabolism is the primary route of elimination for DRP but wide interindividual variation in response is observed. The metabo- lism of DRP was characterized using pooled human liver microsomes (HLMs) and cDNA-expressed CYPs under initial rate conditions at 37°C. In HLMs the decline in DRP concentration was accounted for by formation of two NADPH dependent metabolites (MI and MII). The formation of MI and MII from DRP (0-200lxM) in HLMs followed Michaelis-Menten kinetics (Vmax MI=81.2, Vmax MII= 318.7pmol/min/mg protein). Of the CYP selective inhibitors, only Ketoconazole (llxM), a CYP3A inhibitor, potently inhibited the formation of MI (by 100%) and MII (by 75%) at 5p,M DRP. In a panel of 9 CYPs, the formation of M1 and MII from DRP (5 ~M) was primarily catalyzed by CYP3A4 and CYP3A5. The Km for MII was approximately 141xM for HLMs and expressed CYPs. In conclusion, the data support that DRP is predominantly metabolized by CYP3A4 and CYP3A5 to the MII metabolite. We expect marked increase in the exposure and increased cardiac toxicity of DRP during concom- itant administration of CYP3A inhibitors and loss of efficacy with CYP3A inducers. PI-56 THE EFFECT OF VERAPAMIL ADMINSTRATION ON THE PHARMACOKINETICS OF FEXOFENADINE. G. L. Lemma MD, M. A. Hamman, BS, S. D. Hall, PhD, Z. Wang, MD, PhD, Indiana University School of Medicine, indianapolis, IN. Verapamil (V) is both an inhibitor and inducer of P-glycoprotein (Pgp) and may result in a complex interaction with Pgp. Pgp has a low turn over and complete induction may therefore require extended exposure to inducing drugs. We determined the effect of V on Pgp activity using fexofenadine (F) as a probe. Healthy volunteers (n = 12) received F (60rag) alone or after V dosing (240mg/day po) for 1, 10 and 38 days. F ,and azacyclonol serum and urine concentration were quantified by HPLC with mass spectrometric detection. All subjects showed a significant decrease (P<0.05) in the (mean+/-SD) oral clearance (CLpo, ml/min) of F after a single (1637+/-893) and 10 days (1696+/-674) V treatment compared to controls (2601+/- 1142). The peak serum concentrations (Cmax, ng/ml) of F were significantly increased (P<0.05) by a single (165+/-42) and 10 days (148+/-38.5) V treatment vs. control (114+/-44.6). No significant difference was observed in Cmax and CLpo of F between the control and 38 days of V treatment. Halt-life, renal clearance and fraction unbound of F were not changed. The amount of azacyclonol, a CYP3A4 mediated metabolite of F, eliminated renally decreased from 0.12% to 0.05% of the dose after 10 and 38 days V dosing. We conclude that V short-term administration effectively decreased F oral clearance due to increased F bioavailability caused by inhibition of intestinal P-gp. Long-term treatment with V appears to offset this inhibitory effect.
Transcript of Quantitative prediction of CYP3A-mediated drug interactions.
CLINICAL PHAKMACOLOG¥ & 'I'HEIt2kPEUTICS P 1 6 American Society J:br Clinical Pharmacology and Therapeutics ~Em~UARY 2003
PI-53 QUANTITATIVE PREDICTION OF CYP3A-MEDIATED
DRUG INTERACTIONS. R. E. Kimura, MD~ Y. C. Chen, MD, V. A. Jiyamapa-Sherna, MS, M. A. Hamman, BS, S. D. Hall, PhD, R. E. Galinsky, PharmD, Rush Children's Hospital, Indiana Univer- sity, Purdue University, Chicago, IL.
Drug-drug interactions are the fourth leading cause of death in hospitals. CYP3A enzymes participate in more than half of all drug metabolism pathways and are a common locus of drug interactions in human intestine and liver. In vitro data has many limitations in the prediction of clinically important drug interactions. A novel approach has been developed to predict human drug interactions with midazo- lam (MDZ) using blood sampled simultaneously from the aorta and hepatic vein in chronically catheterized, physiologically stable rats. In vivo estimates in rats of K M for MDZ were 2.9 ug/ml in the presence and 1.3 ug/ml in the absence of 0.6 ug/ml ketoconazole (KET) using the well-sfirred model. The corresponding estimate of in vivo KET inhibitory potency (Ks) relative to the systemic concentration was 0.48 ug/ml. The in vivo parameters estimated from rat studies and the literature values for KET dose (400 mg p o x 4 d) and systemic concentrations (5 ug/ml) from human studies were used to predict the pharmacokinetics of MDZ and the extent of interaction in hmnans. Drug concentrations were determined by HPLC. These studies indi- cate that the in vivo K~ for KET calculated from rats can be used in a human simulation to predict the effects of KET on MDZ pharma- cokinetics in humans.
Observed Predicted
Control KET Control KET
Cmax (ng/ml) 22-37 90 27 88 AUC (ug/ml rain) 3.9-7.8 62 6 74 tl/2 (h) 2.2-2.8 8.7 2.5 9.6
PI-54 DIFFERENTIAL INHIBITION OF CYP3A4 AND CYP3A5 BY
VERAPAMIL. Y. Wang, PhD, D. R. Jones, PhD, S. D. Hall, PhD, Indiana University-Purdue University at Indianapolis, Indianapolis, IN.
Substantial interindividual differences in CYP3A activity contrib- ute greatly to variation in oral bioavailability and systemic clearance of CYP3A substrates. We have recently shown that verapamil is a mechanism-based inhibitor of CYP3A4. The purpose of this study is to compare the effects of verapamil on CYP3A4 and CYP3A5 activities, and to determine if different CYP3A5 expression levels in the human liver microsomes alter the inhibitory potency of vera- pamil. Testosterone 6[3-hydroxylation was used as a marker of CYP3A activity. The possibility that verapamil forms metabolic intermediate complex (MIC) with CYP3A was assessed using dual beam spectrophotometry. Verapamil was found to inhibit recombi- nant CYP3A4 activity in a time-dependent manner but have little effect on recombinant CYP3A5 activity. Verapamil formed MIC with recombinant CYP3A4 (53% of total cytochrome P450) but not with recombinant CYP3A5 as indicated by the appearance of the charac- teristic peak at 455nm. When human liver microsomes were prein- cubated with verapamil for 20 minutes, CYP3A activities of those that contained CYP3A5 in addition to CYP3A4 were reduced by only 20 to 40%, whereas the activities of those that contained only CYP3A4 were reduced by 70%. These findings indicate that the presence of variable CYP3A5/CYP3A4 enzyme expression in the liver may contribute to the interindividual variability associated with verapamil mediated drug interactions.
PI-55 DROPERIDOL IS PREDOMINANTLY METABOLIZED BY
HUMAN CYP3A ENZYMES. G.L. Lemma, MD, Z. Desta, PhD, D. R. Jones, PhD, J. C. Gorski, PhD, S. D. Hall, PhD, Indiana University School of Medicine, Indianapolis, IN.
Droperidol (DRP) is an antipsychotic drug that prolongs the QTc interval and is used commonly to manage postoperative nausea and vomiting. Metabolism is the primary route of elimination for DRP but wide interindividual variation in response is observed. The metabo- lism of DRP was characterized using pooled human liver microsomes (HLMs) and cDNA-expressed CYPs under initial rate conditions at 37°C. In HLMs the decline in DRP concentration was accounted for by formation of two NADPH dependent metabolites (MI and MII). The formation of MI and MII from DRP (0-200lxM) in HLMs followed Michaelis-Menten kinetics (Vmax MI=81.2, Vmax MII= 318.7pmol/min/mg protein). Of the CYP selective inhibitors, only Ketoconazole (llxM), a CYP3A inhibitor, potently inhibited the formation of MI (by 100%) and MII (by 75%) at 5p, M DRP. In a panel of 9 CYPs, the formation of M1 and MII from DRP (5 ~M) was primarily catalyzed by CYP3A4 and CYP3A5. The Km for MII was approximately 141xM for HLMs and expressed CYPs. In conclusion, the data support that DRP is predominantly metabolized by CYP3A4 and CYP3A5 to the MII metabolite. We expect marked increase in the exposure and increased cardiac toxicity of DRP during concom- itant administration of CYP3A inhibitors and loss of efficacy with CYP3A inducers.
PI-56 THE EFFECT OF VERAPAMIL ADMINSTRATION ON THE
PHARMACOKINETICS OF FEXOFENADINE. G. L. Lemma MD, M. A. Hamman, BS, S. D. Hall, PhD, Z. Wang, MD, PhD, Indiana University School of Medicine, indianapolis, IN.
Verapamil (V) is both an inhibitor and inducer of P-glycoprotein (Pgp) and may result in a complex interaction with Pgp. Pgp has a low turn over and complete induction may therefore require extended exposure to inducing drugs. We determined the effect of V on Pgp activity using fexofenadine (F) as a probe. Healthy volunteers (n = 12) received F (60rag) alone or after V dosing (240mg/day po) for 1, 10 and 38 days. F ,and azacyclonol serum and urine concentration were quantified by HPLC with mass spectrometric detection. All subjects showed a significant decrease (P<0.05) in the (mean+/-SD) oral clearance (CLpo, ml/min) of F after a single (1637+/-893) and 10 days (1696+/-674) V treatment compared to controls (2601+/- 1142). The peak serum concentrations (Cmax, ng/ml) of F were significantly increased (P<0.05) by a single (165+/-42) and 10 days (148+/-38.5) V treatment vs. control (114+/-44.6). No significant difference was observed in Cmax and CLpo of F between the control and 38 days of V treatment. Halt-life, renal clearance and fraction unbound of F were not changed. The amount of azacyclonol, a CYP3A4 mediated metabolite of F, eliminated renally decreased from 0.12% to 0.05% of the dose after 10 and 38 days V dosing. We conclude that V short-term administration effectively decreased F oral clearance due to increased F bioavailability caused by inhibition of intestinal P-gp. Long-term treatment with V appears to offset this inhibitory effect.
