Amlodipine metabolism in human liver microsomes and roles of CYP3A4/5 in the dihydropyridine dehydrogenation

Article abstract of DOI:10.1124/dmd.113.055400

Amlodipine is a commonly prescribed calcium channel blocker for the treatment of hypertension and ischemic heart disease. The drug is slowly cleared in humans primarily via dehydrogenation of its dihydropyridine moiety to a pyridine derivative (M9). Results from clinical drug-drug interaction studies suggest that CYP3A4/5 mediate metabolism of amlodipine. However, attempts to identify a role of CYP3A5 in amlodipine metabolism in humans based on its pharmacokinetic differences between CYP3A5 expressers and nonexpressers failed. Objectives of this study were to determine the metabolite profile of amlodipine (a racemic mixture and S-isomer) in human liver microsomes (HLM), and to identify the cytochrome P450 (P450) enzyme(s) involved in the M9 formation. Liquid chromatography/mass spectrometry analysis showed that amlodipine was mainly converted to M9 in HLM incubation. M9 underwent further O-demethylation, O-dealkylation, and oxidative deamination to various pyridine derivatives. This observation is consistent with amlodipine metabolism in humans. Incubations of amlodipine with HLM in the presence of selective P450 inhibitors showed that both ketoconazole (an inhibitor of CYP3A4/5) and CYP3cide (an inhibitor of CYP3A4) completely blocked the M9 formation, whereas chemical inhibitors of other P450 enzymes had little effect. Furthermore, metabolism of amlodipine in expressed human P450 enzymes showed that only CYP3A4 had significant activity in amlodipine dehydrogenation. Metabolite profiles and P450 reaction phenotyping data of a racemic mixture and S-isomer of amlodipine were very similar. The results from this study suggest that CYP3A4, rather than CYP3A5, plays a key role in metabolic clearance of amlodipine in humans. Copyright

Full text of DOI:10.1124/dmd.113.055400

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http://dx.doi.org/10.1124/dmd.113.055400
DRUG METABOLISM AND DISPOSITION
Drug Metab Dispos 42:245–249, February 2014
Copyright ª 2013 by The American Society for Pharmacology and Experimental Therapeutics
Short Communication
Amlodipine Metabolism in Human Liver Microsomes and Roles of
CYP3A4/5 in the Dihydropyridine Dehydrogenations
Received October 15, 2013; accepted December 3, 2013
ABSTRACT
Amlodipine is a commonly prescribed calcium channel blocker for
the treatment of hypertension and ischemic heart disease. The drug
is slowly cleared in humans primarily via dehydrogenation of its
dihydropyridine moiety to a pyridine derivative (M9). Results from
clinical drug-drug interaction studies suggest that CYP3A4/5
incubation. M9 underwent further O-demethylation, O-dealkylation,
and oxidative deamination to various pyridine derivatives. This
observation is consistent with amlodipine metabolism in humans.
Incubations of amlodipine with HLM in the presence of selective
P450 inhibitors showed that both ketoconazole (an inhibitor of
mediate metabolism of amlodipine. However, attempts to identify CYP3A4/5) and CYP3cide (an inhibitor of CYP3A4) completely
a role of CYP3A5 in amlodipine metabolism in humans based on
its pharmacokinetic differences between CYP3A5 expressers and
blocked the M9 formation, whereas chemical inhibitors of other
P450 enzymes had little effect. Furthermore, metabolism of
nonexpressers failed. Objectives of this study were to determine amlodipine in expressed human P450 enzymes showed that only
the metabolite profile of amlodipine (a racemic mixture and
S-isomer) in human liver microsomes (HLM), and to identify
the cytochrome P450 (P450) enzyme(s) involved in the M9
CYP3A4 had significant activity in amlodipine dehydrogenation.
Metabolite profiles and P450 reaction phenotyping data of a race-
mic mixture and S-isomer of amlodipine were very similar. The
formation. Liquid chromatography/mass spectrometry analysis results from this study suggest that CYP3A4, rather than CYP3A5,
showed that amlodipine was mainly converted to M9 in HLM
plays a key role in metabolic clearance of amlodipine in humans.
Introduction
in rats and dogs (Beresford et al., 1988b). It has been reported that many
dihydropyridine analogs undergo CYP3A4-mediated dehydrogenation
to form the corresponding pyridine metabolites in vitro (Guengerich
et al., 1991). However, information on in vitro metabolism of amlodipine
in humans, including P450 reaction phenotyping data, is not available in
the literature.
Amlodipine, a dihydropyridine calcium channel blocker, is one of
the most commonly prescribed drugs for the treatment of hypertension
and ischemic heart disease. In a clinical study, amlodipine shows
a long elimination of half-life (35 hours) after a single 10-mg
intravenous dose (Abernethy, 1991), likely due to its high volume of
distribution and a low rate of plasma clearance. The drug also exhibits
a good oral bioavailability in the range of 52%–88% following a
single 10-mg oral dose to human subjects (Faulkner et al., 1986). After
an oral dose of radiolabeled amlodipine to humans, the total radioactivity
recovery is 59.3% in urine and 23.4% in feces (Beresford et al., 1988a;
Stopher et al., 1988). Similarly, 62% and 22.7% of a radiolabeled
intravenous dose is recovered in human urine and faces, respectively.
S-amlodipine is the active component of racemic amlodipine. There
are no significant differences in pharmacodynamic and pharmacoki-
netic parameters after a single dose of 5 mg of S-amlodipine and
10 mg of amlodipine racemate (Kim et al., 2010). The amlodipine
pyridine metabolite (Fig. 1C, M9), raised from dehydrogenation of the
dihydropyridine moiety, and its derivatives are major drug-related
components in human urine. The mass balance and metabolite profiling
data suggest that amlodipine dehydrogenation to M9 followed by
multiple oxidative reactions of M9 is the major clearance pathway of
amlodipine in humans. Similar metabolic pathways have been observed
Telaprevir, a potent inhibitor of both CYP3A4 and CYP3A5,
increases the amlodipine mean area under the curve (AUC) by 2.79-
fold and the mean half-life from 41.3 to 95.1 hours when the two
drugs are coadministered (Lee et al., 2011). Similarly, combined
dosing of indinavir and ritonavir, both of which are CYP3A inhibitors,
increases the median amlodipine AUC0-24 by 90% (Glesby et al.,
2005). These clinical drug-drug interaction observations suggest that
CYP3A4/5 enzymes play significant roles in metabolic clearance of
amlodipine in humans. CYP3A4 and CYP3A5 are two major enzymes
of the CYP3A family and have similar catalytic specificities. However,
unlike CYP3A4, CYP3A5 is a polymorphic enzyme. To determine if
CYP3A5 contributes to the metabolism of amlodipine, the pharmaco-
kinetics of amlodipine in CYP3A5 nonexpressers (CYP3A5*3/*3
carriers) and CYP3A5 expressers (CYP3A5*1/*1 and CYP3A5*1/*3
carriers) have been recently determined and compared with each other.
After a single dose of amlodipine, its exposure in CYP3A5 expressers is
slightly higher than that in CYP3A5 nonexpressers (Kim et al., 2006).
However, the AUC and the maximal concentrations of amlodipine in
CYP3A5 nonexpressers are about 2-fold higher than those in CYP3A5
expressers after 5-mg once-daily oral doses for 7 days (Zuo et al., 2013).
Although roles of CYP3A5 in the disposition and elimination of
dx.doi.org/10.1124/dmd.113.055400.
s This article has supplemental material available at dmd.aspetjournals.org.
ABBREVIATIONS: AUC, area under the curve; AUC0-24, area under the curve during 24 hours; HLM, human liver microsomes; LC, liquid
chromatography; MH+, protonated molecular ions; MS, mass spectrometry; MSn, multiple stage MS/MS fragmentation; 19-OH-midazolam,
19-hydroxy-midazolam; Thio-TEPA, N,N9,N9-triethylenethiophosphoramide.
245

246
Zhu et al.
Fig. 1. Amlodipine metabolite profile in HLM. (A) UV
profile of metabolites of racemic amlodipine in HLM
(30 mM, 60 minutes, 2 mg protein/ml). (B) MS2
spectrum and the structures of the pyridipine metabolite
(M9). (C) Proposed structures and formation pathways
of amlodipine metabolites in HLM.
for 60 minutes. The reaction mixtures (1 ml) also contained potassium phosphate
buffer (69 mM, pH 7.4) and NADPH (4 mM). Metabolic reactions were
initiated by addition of NADPH after a 3-minute preincubation and stopped
by the addition of 2 ml of acetonitrile. Precipitate was removed by
centrifugation. Supernatant was dried under nitrogen and then reconstituted
in 200 ml of 5% acetonitrile/water (v/v) for LC/mass spectrometry (MS)
analysis.
Time Course of Amlodipine Metabolism in HLM. Racemic amlodipine
and S-amlodipine (1 mM) were separately incubated in duplicates in HLM (1 mg
protein/ml) for 0, 5, 10, 15, 30, and 60 minutes. The reaction mixtures (0.25 ml)
also contained potassium phosphate buffer (69 mM, pH 7.4) and NADPH
(2 mM). Metabolic reactions were initiated by the addition of NADPH after
a 3-minute preincubation and stopped at designated time points by the addition
of 0.5 ml of acetonitrile. Precipitate was removed by centrifugation. Supernatant
was dried under nitrogen and then reconstituted in 50 ml of 5% acetonitrile/water
(v/v) for determination of disappearance of the parent drug and the formation of
the pyridine metabolite (M9).
amlodipine in humans have been suggested by investigators of these
clinical studies, it is very challenging to draw meaningful conclusions
without in vitro P450 phenotyping data of amlodipine. Furthermore,
several studies have investigated the role of CYP3A5 polymorphism in
blood pressure response to amlodipine, but results are not consistent
(Zhang et al., 2013). The major objectives of this study were to determine
the amlodipine metabolite profile in human liver microsomes (HLM)
and P450 enzyme(s) responsible for amlodipine dehydrogenation to
M9. In particular, the roles of CYP3A4 and CYP3A5 in amlodipine
metabolism were investigated. In addition, the in vitro metabolism of
racemic amlodipine was compared with that of S-amlodipine. Results
from this study provide a biochemical basis for better understanding of
the clinically observed amlodipine drug-drug interactions with CYP3A
inhibitors and pharmacokinetics of amlodipine in both CYP3A5 non-
expressers and expressers.
Inhibition of Amlodipine Dehydrogenation HLM by P450 Inhibitors.
Racemic amlodipine and S-amlodipine (1 mM) were separately incubated in
Materials and Methods
Chemicals and Reagents. A racemic amlodipine (2-[(2-aminoethoxy)- HLM (0.5 mg/ml) in triplicates for 13 minutes. Reaction mixtures (0.25 ml)
methyl]-4-(2-chlorophenyl)-1,4-dihydro-6-methyl-3,5- pyridinedicarboxylic acid also contained potassium phosphate buffer (69 mM, pH 7.4), a chemical in-
3-ethyl 5-methyl ester benzene sulfonate norvasc), quinidine, ketoconazole, N, hibitor of P450 enzyme, and NADPH (2 mM). Final concentrations of the P450
N9N9-triethylenethiophosphoramide (Thio-TEPA), montelukast, furafylline, sul- inhibitors were 1 mM for benzylnirvanol, quinidine, ketoconazole, montelukast,
faphenazole, CYP3cide, and benzylnirvanol were purchased from Sigma (St. and CYP3cide; 10 mM for furafylline and sulfaphenazole; and 50 mM for Thio-
Louis, MO). S-amlodipine was purchased from Energy Chemical (Shanghai, TEPA. For the incubations with time-dependent inhibitors (Thio-TEPA,
China). All solvents (acetonitrile, methanol, and water) were of high-performance furafylline, and CYP3cide), the reaction was initiated by the addition of
liquid chromatography (LC) grade. Pooled HLM was obtained from BD
Biosciences (Woburn, MA). Expressed P450 enzymes, CYP1A2, 2B6, 2C8,
2C9, 2C19, 2D6, 3A4, and 3A5 were purchased from BD Biosciences (San
Jose, CA).
amlodipine or S-amlodipine after 10-minute preincubations of HLM and
NADPH in the presence of the individual P450 inhibitors. All other reactions
were initiated by the addition of NADPH after 3-minute preincubations of
HLM with amlodipine or S-amlodipine in the presence of the individual P450
HLM Incubation for Metabolite Profiling. Racemic amlodipine and inhibitors. All of the reactions were stopped by the addition of 0.5 ml of
S-amlodipine (30 mM) were separately incubated with HLM (2 mg protein/ml) acetonitrile, and the precipitate was removed by centrifugation. Supernatants were

Metabolism of Amlodipine by HLM and CYP3A4
247
dried under nitrogen and then reconstituted in 50 ml of 5% acetonitrile/water (v/v) the dehydrogenation metabolite (M9) in the time course, HLM inhibition, and
for LC/MS analysis. metabolism in P450 experiments. In the analysis, full-scan MS data were
Amlodipine Dehydrogenation by Expressed P450 Enzymes. Racemic acquired, and then extracted ion chromatogram at m/z 409 was generated. The
amlodipine and S-amlodipine (1 mM) were separately incubated with individual peak area corresponding to M9 was calculated as the measurement of the relative
expressed human P450 enzymes (100 nM) (CYP1A2, CYP2B6, CYP2C8, abundance of M9.
CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5) in triplicates for 13
minutes. Reaction mixtures (0.25 ml) also contained potassium phosphate
buffer (69 mM, pH 7.4) and NADPH (2 mM). After 3-minute preincubation,
Results and Discussions
metabolic reactions were initiated by the addition of NADPH and stopped by
the addition of 0.5 ml of acetonitrile. Precipitate was removed by centrifugation.
The supernatant was dried under nitrogen and then reconstituted in 50 ml of 5%
acetonitrile/water (v/v) for LC/MS analysis. In addition, racemic amlodipine was
incubated with expressed CYP3A4 and CYP3A5 with or without CYP3cide
under the conditions described earlier. In the same experiment, midazolam (10 mM)
was incubated with expressed CYP3A4 or CYP3A5 (100 nM) in triplicates for
5 minutes. Reaction mixtures (0.04 ml) also contained potassium phosphate
buffer (69 mM, pH 7.4) and NADPH (2 mM). After 3-minute preincubation, the
metabolic reaction converting midazolam to 19-hydroxy-midazolam (19-OH-
Identification of Amlodipine Metabolites Formed in HLM. LC/
MS analysis showed that a total of nine metabolites were formed in
HLM incubations with 30 mM racemic amlodipine or S-amlodipine
(Table 1). M9 and M10 exhibited relatively higher abundances and
accounted for 5.9% and 3.2% of racemic amlodipine, respectively,
based on a UV profile (Fig. 1A). Other metabolites were detectable
only by LC/MS (Supplemental Fig. 1). Protonated molecular ions and
multiple stage MS/MS fragmentation (MSn) spectra of the parent drug
and its metabolites are summarized in Table 1. Based on mass spectral
midazolam) was started by the addition of NADPH and stopped by the addition interpretation and comparisons with those reported in the literature
of 0.08 ml of acetonitrile. Precipitate was removed by centrifugation. Concentrations
of 19-OH-midazolam in the supernatant were quantitatively determined using LC/MS
and 19-OH-midazolam standard.
Liquid Chromatography/Mass Spectrometry Analysis. An LC/MS system
consisted of an LC instrument (Thermo Accela HPLC with a photodiode
array detector; Thermo Fisher Scientific, Waltham, MA) equipped with an
Xbridge C18 column (5 mm, 2.1 Â 150 mm; Waters, Milford, MA) and an ion
trap mass spectrometer (LTQ XL; Thermo Fisher Scientific) was used for
profiling and identification of metabolites formed in HLM. LC separation was
carried out using a mobile phase composed of 0.1% formic acid (v/v) in water
(Suchanova et al., 2006, 2008), metabolite structures and their formation
pathways are proposed in Fig. 1C. For example, the structure of M9 was
ascertained based on the comparison of its MS/MS spectrum (Fig. 1B) to
that of the parent drug (Supplemental Fig. 1) as well as that of the
amlodipine pyridine metabolite reported previously. Amlodipine
dehydrogenation to M9 was the major metabolic pathway in
HLM. M9 underwent further metabolism including oxidative
deamination to M10, O-demethylation to M1, and O-dealkylation to
M4. In addition, amlodipine underwent O-demethylation to M6 and
(solvent A) and 0.1% formic acid in acetonitrile (v/v) (solvent B). A linear monohydroxylation to M3, M5, and M8 (Fig. 1C; Table 1), which
gradient of solvent A starting at 95% to 10% from 0 to 23 minutes was applied
followed by remaining at 10% for 3 minutes before returning to 95%. The
total run time was 30 minutes, and the flow rate was 0.3 ml/min. The mass
spectrometer was operating in the positive electrospray ionization mode in the m/z
range of 100–1000. Capillary temperature was at 275°C. Capillary voltage was
at 46 V. The UV profile of racemic amlodipine and its metabolites in HLM
incubations was acquired at 245 nm for semiquantitative estimation of the relative
abundance of metabolites to the parent drug. Their full-scan MS and MSn data
were acquired using a data-dependent method for metabolite structure
characterization. The same LC/MS instrument and method, except for a short LC
constituted minor pathways in HLM since the metabolites were not
displayed in the UV profile (Fig. 1A). Metabolic profiles of racemic
amlodipine and S-amlodipine in HLM were similar except that
O-demethylation leading to M1 and M6 was not observed for
S-amlodipine (Table 1). The major metabolic pathway observed in
HLM is consistent with the major clearance pathway of amlodipine in
human subjects: amlodipine dehydrogenation followed by oxidations
to multiple metabolites (Beresford et al., 1988a; Stopher et al., 1988).
Time Course of Amlodipine Metabolism in HLM. To optimize
run time (13 minutes), were used for the determination of relative amounts of incubation conditions for assessing the contribution of P450 enzymes
TABLE 1
Summary of amlodipine metabolites detected in HLM by LC/MS
Metabolite
RT
Identity
MH+
MSn Spectral Data
Racemic Amlopdipine
S-amlodipine
min
M1
M3
M4
M5
M6
M8
M9
M10
M12
P
10.06
P-2H-CH2
393
425
336
425
395
425
407
408
422
409
MS2: 376, 350, 332, 314, 304;
MS3 (332): 304, 286
√
√
√
√
√
√
√
√
√
√
2
√
√
√
2
√
√
√
√
√
11.79
12.02
12.06
12.06
12.71
13.57
17.88
18.38
15.02
P + O
MS2: 379, 336, 294, 364;
MS3 (336): 318, 304, 180
MS2: 318,286;
P-2H-C2H4NH-C2H4
P + O
MS3 (318): 286
MS2: 417, 390, 379, 336, 294;
MS3 (336): 318,304,286,181
MS2:352, 334, 306,180;
MS3 (180): 163,144
P-CH2
P + O
MS2: 390, 379, 336, 294, 364;
MS3 (336): 318, 304, 248,181
MS2: 390, 364, 346, 318, 286;
MS3 (346): 318, 286.
P-2H
P-2H-NH+O
P-2H-NH+2O-2H
Amlodipine
MS2: 346,318, 286, 390;
MS3 (346): 318, 286
MS2: 376, 346, 318, 286;
MS3 (346): 318, 286
MS2: 392, 346, 348, 320, 294, 238;
MS3 (392): 360, 346
MH+, protonated molecular ions; MSn, multiple stage MS/MS fragmentation; RT, retention time.

248
Zhu et al.
to amlodipine dehydrogenation, racemic amlodipine and S-amlodipine
were incubated at a lower concentration (1 mM) with HLM,
respectively. Metabolite profiles were determined and time
courses of the M9 formation were semiquantified by LC/MS.
Under the condition investigated, the formation of M9 in HLM
increased linearly with increasing incubation time within 15
minutes. No sequential metabolites of M9 were detected, reinforcing
the idea that M9 is the intermediate to other pyridine derivatives
during amlodipine metabolism. Disappearance of either racemic
amlodipine or S-amlodipine was less than 76% of the initial concen-
trations following 15-minute incubations. Based on these data, 1 mM
substrate concentration and 13-minute incubation time were chosen
for the subsequent P450 reaction phenotyping experiments. It was
expected that the formation of M9 under this condition would be in
a linear range.
Identification of P450 Enzyme Responsible for Amlodipine
Dehydrogenation. As shown in Fig. 2, the formation of M9 from
amlodipine or S-amlodipine was NADPH-dependent and nearly
completely inhibited by ketoconazole, a potent inhibitor of both
CYP3A4 and CYP3A5, and CYP3cide, a potent and selective
inhibitor of CYP3A4 (Walsky et al., 2012). Chemical inhibitors of
other major P450 enzymes, including sulfaphenazole (CYP2C9),
Fig. 3. Relative abundance of M9 formed in incubations of racemic amlodipine and
S-amlodipine with recombinant human P450 enzymes.
benzylnirvanol (CYP2C19), quinidine (CYP2D6), montelukast CYP3A5 were 3.96 and 7.21 (nmol/min/nmol P450), respectively, and
(CYP2C8), furafylline (CYP1A2), and Thio-TEPA (CYP2B6), the relative formation of 19-OH-midazolam in CYP3A4 and CYP3A5
had no or minimal inhibitory effect on amlodipine dehydrogena- was 100:182, which is in agreement with that reported in the literature
tion. Similarly, results from metabolism of racemic amlodipine and (Christensen et al., 2011; Li et al., 2012). In contrast, the relative
S-amlodipine by a panel of expressed P450 enzymes showed that formation of M9 in CYP3A4 and CYP3A5 was 100:11. When
CYP3A4 was the single P450 enzyme catalyzing the formation of M9 CYP3sdie, a CYP3A4-specific inhibitor, was coincubated with
(Fig. 3).
CYP3A4 and CYP3A5, the M9 formation in CYP3A4 was greatly
To further confirm that CYP3A5 has no or minimal catalyzing reduced to the levels in CYP3A5, whereas CYP3cide had no effect
activity toward amlodipine dehydrogenation, the relative formation on the M9 formation in CYP3A5. These results indicate that
rate of M9 from racemic amlodipine in CYP3A4 and CYP3A5 was CYP3A4 is responsible primarily for the formation of M9 via
compared with that of 19-OH-midazolam from midazolam in amlodipine dehydrogenation. CYP3A5 and other P450 enzymes
CYP3A4 and CYP3A5. Midazolam is a substrate of both CYP3A4 have no or little role in catalyzing amlodipine dehydrogenation. The
and CYP3A5. Results from the current study showed that the differences in amlodipine exposures observed between CYP3A5
formation rates of 19-OH-midazolam in expressed CYP3A4 and nonexpressers and expressers (Kim et al., 2006; Zuo et al., 2013)
could be due to differences in CYP3A4 expressions between the two
groups since CYP3A5 has minimal, if any, effect on the in vitro
metabolism of amlodipine (Figs. 2 and 3). The in vitro data also
support an early clinical observation that blood pressure response to
amlodipine among high-risk African Americans appears to be
determined by CYP3A4, but not CYP3A5, genotypes (Bhatnagar
et al., 2010).
In summary, racemic amlodipine and S-amlodipine were slowly
metabolized in HLM. Amlodipine dehydrogenation to the pyr-
idine metabolite (M9) was the single most important metabolic
pathway in HLM; M9 further underwent oxidative deamination,
O-demethylation, and O-dealkylation. These in vitro metabolism
data are consistent with amlodipine metabolism and disposition
observed in vivo in humans. The data derived from amlodipine
metabolism in expressed P450 and HLM with P450 inhibitors
indicate that CYP3A4, not CYP3A5, is the primary contributor to
amlodipine dehydrogenation. Metabolite profiles and P450 re-
action phenotyping data of a racemic mixture and S-isomer of
amlodipine were very similar, consistent with pharmacokinetics of
racemic amlodipine and S-amlodipine in humans. These findings
suggest that the observed clinical drug-drug interactions between
amlodipine and CYP3A4/5 inhibitors are mediated by CYP3A4
rather than CYP3A5. In addition, polymorphic expressions of
CYP3A5 would not affect the pharmacokinetic variability of
amlodipine and the blood pressure response to amlodipine in
Fig. 2. Inhibition of the formation of M9 from racemic amlodipine and S-amlodipine
in HLM by P450 inhibitors.
humans.

Metabolism of Amlodipine by HLM and CYP3A4
249
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Clin Ther 32:193–205.
DMPK Department, Shanghai
ChemPartner, Shanghai, People’s
Republic of China (Y.Z., F.W., Q.L.,
A.D., W.T., W.C.) and Department
of Biotransformation, Bristol-Myers
Squibb, Princeton, New Jersey
(M.Z.)
YANLIN ZHU
FEN WANG
QUAN LI
MINGSHE ZHU
ALICIA DU
WEI TANG
WEIQING CHEN
Kim KA, Park PW, Lee OJ, Choi SH, Min BH, Shin KH, Chun BG, Shin JG, and Park JY (2006)
Effect of CYP3A5*3 genotype on the pharmacokinetics and pharmacodynamics of amlodipine
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Authorship Contributions
Participated in research design: M. Zhu, Chen.
Conducted experiments: Y. Zhu, Li, Wang.
Contributed new reagents or analytic tools: Du.
Performed data analysis: Y. Zhu, Li, M. Zhu, Chen.
Suchanova B, Kostiainen R, and Ketola RA (2008) Characterization of the in vitro metabolic
profile of amlodipine in rat using liquid chromatography-mass spectrometry. Eur J Pharm Sci
33:91–99.
Wrote or contributed to the writing of the manuscript: Y. Zhu, Tang, Chen,
M. Zhu.
Suchanova B, Sispera L, and Wsol V (2006) Liquid chromatography-tandem mass spectrometry
in chiral study of amlodipine biotransformation in rat hepatocytes. Anal Chim Acta 573-574:
273–283.
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Address correspondence to: Weiqing Chen, DMPK Department, Shanghai
ChemPartner, 998 Halei Rd., Zhangjiang Hi-tech PK, Pudong New Area, Shanghai
201203, PR China. E-mail: weiqingchen@chempartner.cn or Mingshe Zhu,
Biotransformation Department, Bristol-Myers Squibb, Princeton, NJ 08543.
E-mail: mingshe.zhu@bms.com