Session 25 : Pharmacologie clinique, Pharmaco-épidémiologie, Pharmacocinétique

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Session 25 : Pharmacologie clinique, Pharmaco-épidémiologie, Pharmacocinétique

242

Cytochrome P450 2C and 3A catalyze the metabolism of Zopiclone. In vitro studY in human liver microsomes and recombinant human enzymes

L. Becquemont1, S. Mouajjah1, P. Beaune2 and P. Jaillon1

1: Clinical Pharmacology Unit, Saint Antoine University Hospital, Paris, France. 2: Unité INSERM U 490, Saints-Pères University, Paris, France.

Zopiclone, one of the major hypnotic drugs prescribed in France, is extensively metabolized by the liver into N-demethyl- (NDM-Z) and Noxide-zopiclone (NO-Z) in humans. The enzymes involved in its metabolism have not yet been identified. We investigated the in vitro metabolism of zopiclone with human liver microsomes and heterologously-expressed human cytochrome P450 (CYP) isoforms (CYPlA2, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4 and 3AS, (kindly provided from the Bioavenir research programm). Using liver microsomes, zopiclone was metabolized into NDM-Z and NO-Z, NDM-Z being the major metabolite. Sulphaphenazole, a CYP2C inhibitor, and Troleandomycin, a CYP3A inhibitor resulted in a 86% and 40% inhibiton of zopiclone metabolism into its major metabolite NDM-Z respectively, whereas quinidine,

al-naphtoflavone and chlorzoxazone did not significantly modify its metabolism.

NDM-Z

NO-Z

Vm

Km

Vm

Km

Human liver

0.83

± 0.04 (pm/min/mg)

92

± 12 µM

0.16

± 0.01 (pm/min/mg)

70

± 9 µM

rH-CYP2C8

0.32

± 0.02 (pm/min/pm)

124

± 15 µM

0.2

± 0.01 (pm/min/pm)

63

± 7 µM

Screening of zopiclone metabolism using different human CYP expressed in yeast, indicated that CYP2C8 was the major CYP isoform implicated in NDM-Z generation. The metabolism of zopiclone into NO-Z was mainly catalyzed by CYP2C9 and CYP3A4. Extrapolation of the results of zopiclone metabolism obtained with recombinant CYP to human liver microsomes indicated that CYP2C9 was the major CYP isoform implicated in zopiclone metabolism, followed by CYP3A4 > CYP2C8. We conclude that CYP2C9 and CYP3A are involved in the metabolism of zopiclone in vitro.

243

ARE CYSTEAMINE HYDROCHLORIDE, CYSTEAMINE BITARTRATE AND PHOSPHO-CYSTEAMINE EQUIVALENT ? A STUDY IN HEALTHY VOLUNTEERS

L. Tennezé1, V. Daurat2, A. Tibi3, P. Chaumet-Riffaud2, C. Funck-Brentano1

1. Clinical Investigation Centre, St-Antoine University Hospital; 2. Délégation à la Recherche Clinique, St-Louis Hospital; 3. Central Hospital Pharmacy. Assistance Publique – Hôpitaux de Paris, Paris, FRANCE.

Cysteamine (Cys) is the only treatment of cystinosis in pediatric patients. Cys is available as the hydrochloride (Cys-HCl), the bitartrate (Cys-Bitar) salts and as phosphocysteamine (Cys-Phos). It has been suggested that Cys-Bitar and Cys-Phos are better tolerated and may have a better bioavailability than CysHC1. This has, however, never been clearly demonstrated. We therefore conducted a double-blind, latin-square, 3-period cross-over bioequivalence study in 18 healthy male adult volunteers. Each subject received one single oral dose (15.55 mM of Cys base) of each Cys form as 11 capsules. Each study period was separated by a 3-day drug-free interval. Plasma concentrations of Cys were determined with a sensitive and specific HPLC assay over a 12 hour period following each administration. Gastro-intestinal tolerance was assessed by counting vomiting episodes. The table gives the relative bioavailability (F) (mean

± SD) and the 90 % CI for the ratios of AUC0-¥ and observed Cmax for each drug-couple.

CI for AUC0-

¥ (%)

CI for Cmax (%)

F (%)

Cys-Phos /Cys-HCl

83 – 106

76 – 106

97

± 25

Cys-Bitar/Cys-HCl

90 – 117

74 – 124

105

± 24

Cys-Bitar/Cys-Phos

95 – 125

92 – 126

112

± 27

No statistical difference was found between relative bioavailabilities, AUC, tmax and Cmax with each of the three forms of cysteamine tested. Cysteamine salts were bioequivalent (Confidence Intervals within 80-125%), except for their Cmax. The only significant adverse event was vomiting whose frequency was inversely correlated with body weight (rhô=- 0.76, p