Genotype-phenotype associations of
cytochrome P450 3A4 and 3A5
polymorphism with midazolam clearance
in vivo
The molecular basis for the wide interindividual variability of cytochrome P450 (CYP) 3A metabolic activity
was studied in vivo at a genetic level. A single oral dose of midazolam was administered to 26 healthy subjects.
The variability in midazolam oral clearance was 11-fold. No differences in midazolam oral clearance related
to gender or ethnicity were observed. Selective sequencing of CYP3A4 and CYP3A5 genes revealed 18 single
nucleotide polymorphisms (SNPs), including 8 novel CYP3A4 SNPs. Thirteen novel CYP3A4 haplotypes, 2
novel CYP3A5 haplotypes, and 1 major novel multigene haplotype (CYP3A4*VI-CYP3A5*3A) were also
identified. No significant genotype-phenotype or haplotype-phenotype associations were found for any of the
SNPs or haplotypes studied, including CYP3A4*1B, CYP3A5*3, and CYP3A5*6, even when ethnicity was
considered. The only exceptions were the haplotype CYP3A4*VI and the multigene haplotype CYP3A4*VI-
CYP3A5*3A. The carriers of the haplotype CYP3A4*VI had a 1.8-fold higher clearance of midazolam in
black subjects (ANOVA on ranks, P .028) compared with other individuals, and the carriers of the
multigene haplotype CYP3A4*VI-CYP3A5*3A had a 1.7-fold higher clearance in the entire population
(ANOVA on ranks, P .012). In conclusion, these results indicate that the genetic variants identified so far
in the CYP3A4 and CYP3A5 genes have only a limited impact on CYP3A-mediated drug metabolism in vivo.
(Clin Pharmacol Ther 2005;77:373-87.)
Ping He, MD, Michael H. Court, BVSc, PhD, David J. Greenblatt, MD, and
Lisa L. von Moltke, MD Boston, Mass
The human cytochrome P450 (CYP) 3A subfamily is
responsible for metabolizing approximately half of the
currently marketed drugs, as well as steroids, environ-
mental chemicals, and carcinogens.
1-4
Four members of
the CYP3A subfamily, CYP3A4,
5-7
CYP3A5,
6,7
CYP3A7,
8
and CYP3A43,
9
have been identified.
CYP3A4 is the major form present in the liver and
intestinal epithelium.
10
CYP3A5, a polymorphic form,
is present in the livers of approximately 20% of white
subjects
11
and in more than 50% of black subjects.
12,13
CYP3A5 is also distributed in other tissues, including
the intestine and kidney.
1,14,15
CYP3A7 is the fetal
form of CYP3A and is believed to be of low abundance
in the adult liver and other tissues.
16
CYP3A43 is
expressed at the highest level in the prostate,
9
but its
hepatic messenger ribonucleic acid (mRNA) level is
only 0.2% to 5% of that of CYP3A4.
9,17
Interindividual variability in the expression and ac-
tivity of CYP3A is considerable. In vivo studies have
shown 5-fold variability in the clearance of midazo-
lam
10
and even larger (10-fold) variability in the
metabolism of other CYP3A substrates.
1,18-20
Variabil-
ity in the rate of hepatic oxidation of CYP3A substrates
in vitro is even larger (30-fold).
21
Environmental
agents
19
and coadministered drugs,
22-25
as well as con-
stituents of food such as grapefruit juice,
26
may play a
role. Estimation of the relative contribution of genetic
variation to CYP3A function indicates that 70% to 90%
From the Division of Clinical Pharmacology and Comparative and
Molecular Pharmacogenetics Laboratory, Department of Pharma-
cology and Experimental Therapeutics, Tufts University School of
Medicine, and Tufts-New England Medical Center.
This study was supported by grants AG-17880, AT-01381, MH-
58435, GM-61834, DA-13209, DK-58496, DA-05258, and RR-
00054 from the Department of Health and Human Services.
Received for publication July 13, 2004; accepted Nov 18, 2004.
Reprint requests: David J. Greenblatt, MD, Department of Pharma-
cology and Experimental Therapeutics, Tufts University School of
Medicine, 136 Harrison Ave, Boston, MA 02111.
E-mail: dj.greenblatt@tufts.edu
0009-9236/$30.00
Copyright © 2005 by the American Society for Clinical Pharmacology
and Therapeutics.
doi:10.1016/j.clpt.2004.11.112
373