Pharmacology & Pharmacy, 2011, 2, 31-41
doi:10.4236/pp.2011.21004 Published Online January 2011 (http://www.SciRP.org/journal/pp)
Copyright © 2011 SciRes. PP
31
Gender Differences in the Pharmacokinetics of
Oral Drugs
Miriam del Carmen Carrasco-Portugal1, Francisco Javier Flores-Murrieta1,2
1Unidad de Investigación en Farmacología, Instituto Nacional de Enfermedades Respiratorias Ismael Cosío Villegas. México, D.F.,
México; 2Sección de Estudios de Posgrado e Investigación, Escuela Superior de Medicina del Instituto Politécnico Nacional. México,
D.F., México.
Email: fjfloresmurrieta@yahoo.com.mx, fjfloresmurrieta@prodigy.net.mx
Received November 3rd, 2010; revised November 13th, 2010; accepted November 30th, 2010
ABSTRACT
Establishment of rational dosage regimens requires the knowledge of pharmacokinetics and pharmacodynamics in the
target population. It has been established that side effects produced by drugs are more frequent in women than in men.
This may be due to two possibilities, one is that normalized dose received by women is higher than men and the other is
that anatomical and physiolog ical cha ra cteristics a re a quite different. In this review, some aspects that may play a role
in the generation of such differences are analyzed, including the impact on absorption, distribution, metabolism and
excretion of drugs. Most of the changes can be explained by differences in volume of distribution and systemic clear-
ance, however, presystemic clearance also seems to play a role in such dissimilarities. The final result, in general, is
that women have higher plasma levels of drugs and usually these differences are reduced or abolished when data are
normalized by the body weight, since both, volume of distribution and systemic clearance are influenced by it; however,
there are some cases in which differences remain. Further research oriented to establish the role of each of the ana-
tomical and physiological differen ces in the oral pharmacokinetics of drugs is warranted.
Keywords: Gender-Related Differences, Oral Pharmacokinetics, Sex Differences
1. Introduction
During the past decade, pharmacological research has
greatly enhanced our understanding of several variables
affecting the prescription of medication. One variable of
increasingly recognized importance is gender. Up to 5%
of all hospital admissions and up to 7000 deaths annually
in the United States are the result of adverse drug reac-
tions (ADRs) [1]. Identifying those factors that may pre-
dispose to ADRs are essential for risk management.
Amongst the known risk factors for adverse drug reac-
tions are increasing age, polypharmacy, liver and renal
disease as well as being female. However, the reasons for
this increased risk in female patients are not entirely clear
but include gender related differences in pharmacokinet-
ics, pharmacodynamics, immunological and hormonal
factors as well as differences in the use of medications by
women compared with men.
Female has been shown to be a risk factor for clini-
cally relevant adverse drug reactions with a 1.5 to
1.7-fold greater risk of developing an adverse drug reac-
tion compared to male patients [2]. The question is this
distinction with the man is due to pharmacokinetics
and/or pharmacodynamics differences or do females just
receive more medication and higher doses than males?,
or both actions play a role in these differences.
Initial drug concentrations after a bolus dose or load-
ing dose and maximum peak concentrations (Cmax) are
dependent on the volume of distribution (Vd). Average
steady-state concentrations (Css) are dependent on clear-
ance (Cl). For the majority of drugs, Vd and Cl are de-
pendent on body weight; yet few drugs are dosed based
on body weight. Generally, males weigh more than fe-
males. Therefore, based on differences in body weight
alone, females often receive higher doses which results in
higher concentration and drug exposure than males, ire-
spective of other pharmacokinetic differences.
The first medication to be gender analyzed for phar-
macokinetic differences was antipyrine in 1971 [3], this
drug is eliminated entirely by hepatic metabolism, and
the study showed that the half life of antipyrine was
shorter in women. The next drug to be analyzed was
acetaminophen, the clearance of this drug was faster in
men than in women. In the past, women have been un-
Gender Differences in the Pharmacokinetics of Oral Drugs
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32
derrepresented in clinical trials, which have caused a
relative lack of data to evaluate possible sex differences
in drug efficacy and side effects. A main reason for this
underrepresentation is the fear of potential teratogenicity.
As a result, major studies involving the efficacy of drugs
did not include women. The FDA includes more women
in clinical trials since 2000 [4]. Since then, growing in-
formation about the influence of gender in the pharma-
cokinetics of drugs has been published.
It is well known that there are important physiological
differences between women and men, that may produce
differences in the pharmacokinetics of drugs, since all
processes involved in the absorption, distribution, me-
tabolism and excretion of drugs may be changed. In this
review, an analysis about the influence of gender in these
factors is carried out.
2. Absorption
Drug absorption is defined as the pass from the site of
administration to the systemic circulation. Depending on
the route of administration, the drug has to cross several
barriers that may contribute to reduce the bioavailability.
When the drug is administered intramuscularly, the pos-
sibility of a wrong administration is higher than in men.
When the drugs are given orally, it has clearly estab-
lished that gastric acid secretion, gastric emptying time,
gastrointestinal blood flow, presystemic metabolism and
transporters activity influence the absorption of drugs
[5,6]. Although there is little information concerning
changes due to gender in such factors, it has been estab-
lished that changes in the bioavailability of several
sustances may occur [7-10]. It has been reported that
some hormones may modify gastric acid secretion, and
therefore gastric pH, and additionally, a slower gastric
emptying time is present in females [11,12]. The cones-
quence of such changes is that a significative delay of the
onset of effectiveness of enteric-coated dosage forms and
drug solubility and dissolution rate may be modified [13].
However, contradictory results have been published since
there is evidence indicating that no change in the phar-
macokinetic parameters is observed in several studies. As
it can be seen, it is not possible to predict a priori in
which cases differences between women and men in the
absorption of enteric coated formulations will be present,
since several factors may contribute to the possible gen-
der differences, and it is a quite difficult to establish if
differences are due to these factors.
Other factor that may contribute to gender differences
in the pharmacokinetics of drugs is the gastrointestinal
blood flow [14]. It has been described that usually
women have lower organ blood flow. The theoretical
consequence of this diminished flow may be a slower
rate and probably lower extent of drug absorption [15].
However, to our knowledge, there are no available data
evaluating the influence of this reduced gastrointestinal
blood flow described in women on the oral pharmacoki-
netics of drugs.
Additionally to the described aspects that may modify
the oral absorption of drugs, presystemic metabolism
may influence importantly the bioavailability of drugs. It
has been described that the major oxidative enzymatic
pathway involved is the intestinal CYP3A4. In this case,
controversial results have been published. On one hand,
it has been suggested that no significative sex-related
difference in the activity and/or content of gastrointesti-
nal CYP3A4 is observed [16,17], and therefore, no dif-
ference in the bioavailability of drugs due to this pathway
is expected; but, on the other hand, in an elegant study
carried out with verapamil, it has been demonstrated that
presystemic metabolism was, at least partially response-
ble of the gender differences observed after administra-
tion of this drug orally [18]. These authors concluded
that sex-differences in drug metabolism occur in both the
gut and the liver and involve multiple metabolic path-
ways and an important thing is that pharmacokinetic dif-
ferences will alter the pharmacodynamic responses.
Studies oriented to evaluate both, presystemic and sys-
temic metabolism surely will contribute to clarify the
exact role of each of them in the gender-related differ-
ences in the pharmacokinetics of orally administered
drugs.
A situation that has produced confusion about the role
of presystemic metabolism is that most of drugs metabo-
lized by CYP3A4 are also substrates of P-glycoprotein
(Pgp), an efflux pump that reduce the bioavailability of
drugs. In this case, also contradictory results have been
reported. Results described by some authors indicate that
activity is one-third to one-half lower in livers obtained
from females compared with males [19], however in
other in vitro study there were no difference in the ex-
pression of Pgp [20]. It is not easy to establish the role of
Pgp in the gender-related differences in the oral pharma-
cokinetics of drugs for the above mentioned that CYP3A4
and Pgp share substrates. An interesting group of drugs
that are substrates of Pgp and that are not metabolized by
CYP3A4 are the fluoroquinolones [21,22]. Several stud-
ies have been carried out comparing the influence of
gender on the oral pharmacokinetics of several drugs
from this group, named ciprofloxacin, ofloxacin, levo-
floxacin, grapefloxacin and gatifloxacin. In all cases,
higher plasma levels were reached in women when com-
pared with men [23-27], but differences dissapear when
data were normalized by the body weight of individuals.
These results taken together seem to indicate that Pgp
does not play an important role in the gender-related dif-
ferences in the oral pharmacokinetics of drugs. However,
Gender Differences in the Pharmacokinetics of Oral Drugs
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33
it can not be completely ruled out as a genesis of sex-
related differences in the oral pharmacokinetics of drugs.
Since several factors may contribute to gender differ-
ences in the absorption of drugs, the final result will de-
pend on the characteristics of the compound and the ex-
tent of gender differences of each of the factors described.
It is necessary further research oriented to establish
which of the above mentioned factors have a major con-
tribution to the gender-related differences in the oral
pharmacokinetics of drugs.
3. Distribution
It is well known that gender differences in the composi-
tion of body are present. Some of the differences are
body mass index, percent of body fat, plasma volume and
organ blood flow [28,29]. It has been described that
women have lower average body weight, higher body fat
percentage, smaller average plasma volume and lower
average organ blood flow than men [28-30]. As a result
of these disparities, important distribution differences
between genders are observed [30]. Other factor that may
contribute to gender differences in distribution of drugs
is the protein binding, since major protein groups re-
sponsible for binding drugs are influenced by concentra-
tion of sex hormones and therefore, changes in distribu-
tion may occur between genders and during the men-
strual cycle [31,32].
As a general rule, water-soluble compounds are more
widely distributed in men than in women, since water
content of men, normalized by the body weight, is about
15 to 20% higher than women. Some examples of this
situation are fluconazole [33] and metronidazole [34], in
which volume of distribution is bigger in men when
compared with women, and such differences remain,
although normalization by weight is carried out [33,34].
On the contrary, hydrophobic drugs are more widely dis-
tributed in women, due to higher fat percentage content
[30]. However, most of the times, changes in volume of
distribution of the drug are completely abolished when
the parameter is normalized by the body weight. But the
main concern is that usually, dosage regimens employed
for most of the currently used drugs are not normalized
by the body weight of individuals and this situation may
explain, at least in part, the increased concentrations and
therefore more frequency of side effects observed in
women.
4. Metabolism
Probably, metabolism of drugs has received the main
attention to explain gender differences in the pharma-
cokinetics of drugs. It has been described that activity of
several enzymatic pathways is reduced in women when
compared with men, whereas in other cases, other path-
ways are increased in women. It is important to note that,
enzymatic activity is not the only factor that influences
the metabolism of drugs, and important contribution to
this metabolism is given by the blood flow and protein
binding of the drug. Hepatic metabolism is divided in
two different kind of reactions, named phase I and phase
II. Phase I reactions are oxidation, reduction and hy-
drolysis, whereas, phase II metabolic reactions include
acetylation, sulfation, glucuronidation and methylation.
Quantitatively, cytochrome P-450 (CYP) mediated oxi-
dation is the major reaction and it has been described
gender differences in several isozymes of this CYP. It
has been reported that CYP3A4 is the major isozyme of
this enzymatic pathway and is responsible of the metabo-
lism of about 50% of the current used drugs [35], being
for this reason the most important CYP. Controversial
results have been published concerning the activity of
this enzyme. On one hand, several authors have sug-
gested (based on in vitro studies) that CYP3A4 activity is
higher in women than in men, whereas CYP1A2 and
CYP2D6 activity is higher in men, and no differences or
contradictory results have been reported in other CYPs.
Table 1 shows hepatic CYP and UDP-glucuronosyl-
transferase activity according to gender. However, al-
though these differences have been reported in vitro,
frequently they are not reflected in vivo, and therefore,
contradictory results have been published. A summarized
description of gender-related differences depending on
the metabolic pathway, in which gender-related differ-
ences in the activity have been suggested, is given.
CYP1A2. This isozyme is responsible of the oxidative
metabolism of several drugs including clozapine, olan-
zapine, theophylline and ondansetron. This CYP is the
most induced isozyme by smoking [36]. It has been sug-
gested that activity of this CYP is increased in men when
compared with women. The result of this difference is
Table 1. Comparative activity of different enzymatic path-
ways between genders.
ENZYMATIC PATHWAY ACTIVITY
CYP1A2 M > F
CYP2C9 M = F
CYP2C19 M > F, M = F, F > M*
CYP2D6 M = F
CYP2E1 M > F
CYP3A4 F > M, M = F*
UGT M > F
M = males, F = females; *contradictory results have been published.
Gender Differences in the Pharmacokinetics of Oral Drugs
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34
that higher levels of the drugs metabolized by this
isozyme are observed in women. Examples of such dis-
parities are observed with clozapine and olanzapine, in
both cases plasma levels were higher in women and the
potential of side effects is increased [37-39]. Similar re-
sults were observed when oral pharmacokinetics of on-
dansetron was compared between women and men, i.e.
significative higher levels were reached in women [40].
Taken together, data reported indicate that CYP1A2 ac-
tivity is higher in men compared with women, and
therefore, it should be desirable to establish different
dosage regimens based on the patient’s gender.
CYP2C9. This is a polymorphic isozyme that is respon-
sible of the metabolism of a wide variety of drugs, include-
ing phenytoin, several non-steroidal anti-inflammatory
drugs (NSAIDs) (diclofenac, ibuprofen, piroxicam), and
sulfonylureas (glyburide, glimepiride and glipizide). Al-
though this is a polymorphic isozyme, evidence pub-
lished seems to indicate that no gender-related differ-
ences are present, since no changes in oral pharmacoki-
netics of drugs metabolized by this pathway have been
reported, including phenytoin, ibuprofen, tolbutamide,
glyburide and ketoprofen [41,42]. However, a study car-
ried out by Meyer et al. [43] described lower plasma lev-
els of phenytoin when concentrations were normalized
by the body weight, suggesting increased CYP2C9 activ-
ity in women. As it can be seen, contradictory results
have been published, indicating that further studies ori-
ented to clearly establish a possible gender-related dif-
ference in this enzymathic pathway should be carried out
taken into account the body weight of individuals.
CYP2C19. This is also a polymorphic isozyme that is
responsible of the metabolism of S-mephenytoin, diaze-
pam and proton-pump inhibitors, including omeprazole,
lansoprazole and pantoprazole [44]. So far, contradictory
results have been reported concerning the gender-related
differences in its activity. Some authors indicated that
females have more activity than males, however, in other
studies it has been reported that women have lower ac-
tivity in comparison with men, and some authors indicate
that no difference is observed [45]. There are several
confusing factors that could explain these contradictory
results, including the probe employed, ethnicity, and the
intake of oral contraceptives [45]. Although most of the
authors have reported that women have less activity in
CYP2C19, further studies are required in order to clarify
if there are gender-related differences in the activity of
this important isozyme.
CYP2D6. Other polymorphic isozyme is CYP2D6 and
is responsible of the oxidative metabolism of several
drugs including betablockers, some analgesic, antiar-
rhytmics and antidepressants [46]. There is limited in-
formation concerning the possible gender-related differ-
ences in the activity of this isozyme. On one hand, it has
been reported that no changes due to gender are present
[47], however, when oral pharmacokinetics of metoprolol
(a drug that is metabolized by CYP2D6) was compared
between women and men, higher levels of metoprolol
were found in women, indicating a higher metabolism in
men, however, in other study no changes were observed
[48-50]. These contradictory results do not allow us rule
out gender-related differences in the oral pharmacokinet-
ics of drugs metabolized by CYP2D6. Although most of
the evidence indicate a lack of gender-related differences
in the CYP2D6 activity, further studies are necessary in
order to clarify this doubt.
CYP2E1. This isozyme has producing a growing in-
terest due to its polymorphism and the consequences of
such variability. This pathway is responsible of the me-
tabolism of ethanol, chlorzoxazone and some anesthetics
such as halothane, isoflurane, diethylether and methoxy-
flurance [51-52]. The activity of this isozyme has been
measured as the ratio of 6-hydroxychlorzoxazone/chlor-
zoxazone, and it has been described that women have
about 30% lower activity than men [45]. The importance
of such difference in activity of CYP2E1 in the sex-related
differences in the pharmacokinetics of drugs remains to
be elucidated. This may be due to the low number of
substrates of this isozyme and the route of administration
usually employed in most of these compounds.
CYP3A4. This isozyme is the most abundant CYP in
the human liver and intestinal tract. Additionally, it is
responsible of the oxidative metabolism of at least 50%
of the current used drugs [35]. That is why, it has been
widely studied. It has been described that activity of this
isozyme is 20 to 50% higher in women when compared
with men [45]. However, other authors have not found
any difference between genders when oral pharmacoki-
netics of drugs has been compared [47,53,54]. Addition-
ally to these studies, it has been evaluated the differences
in the urinary excretion of 6-betahydroxycortisol/cortisol
(a marker of hepatic CYP3A4) in Asian and Caucasian
women [55]. In this study, differences between popula-
tions were found and this may be a confusing factor that
may play a role in the evaluation of possible gender dif-
ferences in the oral pharmacokinetics of drugs. An addi-
tional factor is the wide variability found in the activity
of this enzymatic pathway, as well as, the possible role of
Pgp in the generation of the differences. In this way, it
has been suggested that no differences are observed in
CYP3A4 activity between genders and that the differ-
ences are completely explained by different activity of
hepatic Pgp in women [56]. Due to these controversial
results, further studies oriented to establish the role of
CYP3A4 and Pgp in these gender-related differences are
necessary. This is a big challenge since these systems
Gender Differences in the Pharmacokinetics of Oral Drugs
Copyright © 2011 SciRes. PP
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share substrates and the net result obtained in vivo is a
mixture of the participation of both systems.
UDP-glucuronosyl transferases (UGT). This is a group
of isozymes that is formed by two families. It has been
suggested that activity of UGT activity may be reduced
in females compared with males, based on elimination of
temazepam, oxazepam, acetaminophen, clofibric acid,
diflunisal, labetalol and mycophenolic acid [57]. This
information is limited to conclude which of the families
of UGP may be involved in such differences and further
studies are required to establish the role of these dissimi-
larities in therapeutics.
5. Excretion
Excretion of drugs can be carried out by several path-
ways, however, renal excretion is one of the most impor-
tant routes of drug excretion. Glomerular filtration rate
(GFR) is lower in women than in men, moreover, after
normalizing GFR by the body size, a 10% difference
remains [58] and therefore, renal clearance may be di-
minished for a wide variety of drugs. Concerning other
mechanisms involved in the renal clearance, it has been
reported sex-related differences in the tubular secretion
and reabsorption. It has been established that clearance of
taurocholate is increased in female rats when compared
with male rats, indicating an increased reabsorption
process in females [59,60]. In addition, it has been also
reported increased urinary excretion of organic anions in
female rats in comparison with male rats [60-62] indi-
cating that renal clearance of organic anions may be in-
creased in females. However, in general renal clearance
observed in women is lower than the values obtained in
men. Probably this may be due to the increased GFR
observed in men that seems to have the major role in the
renal clearance of drugs.
Impact of gender-related differences in the oral phar-
macokinetics of drugs
As mentioned above, there are an important number of
factors that may contribute to the gender differences in
the pharmacokinetics of drugs. The final result will be in
function of the different mechanisms involved in the ab-
sorption, distribution, metabolism and excretion of the
drug. As stated above, gender-related differences seem to
be due to several factors. On one hand, dosage regimens
usually are given without normalizing by the body
weight, having as a consequence higher doses in women
in comparison with men. On the other hand, there are
several physiological conditions that are different be-
tween genders and that are reflected in disimilarities in
the oral pharmacokinetics of drugs. Probably the two
parameters that are more affected by this situation are
volume of distribution and systemic clearance. It has
been reported that major molecular differences between
mammalian sexes are involved in drug metabolism and
renal function [63]. Both depend on the individual body
weight. However, there are other physiological charac-
teristics that may influence them. Additionally to body
weight of the individual, volume of distribution is the
result of protein and tissue binding, body fat and plasma
volume. At least binding and body fat may be dissimilar
in women in comparison with men, resulting in different
distribution profile [28-31]. These characteristics leads to
gender-related differences in the pharmacokinetics and
therefore to a different effect profile. In addition to the
distribution differences, systemic clearance plays a major
role in the pharmacokinetic differences between genders
[11,30,45]. As known, systemic clearance is the sum of
all organs clearance, being the most important hepatic
and renal clearances. In addition, the role of presystemic
clearance (due to Pgp or gut metabolism) should not be
ruled out, since in some cases it is very important in the
reduction of bioavailability and may be responsible of
gender-related differences in the oral pharmacokinetics
of drugs.
In the last years, a growing interest in the gender dif-
ferences in the pharmacokinetics has resulted in studies
designed to elucidate the possible differences. However,
contradictory results have been obtained. There are sev-
eral reasons that may explain these contradictions. Usu-
ally, studies are carried out in small groups of subjects,
normalized administered dose employed is different, it is
not controlled the use of oral contraceptives and some
other factors that may have influence in the results. Al-
though these limitations, in the cases in which gen-
der-related differences were observed, it has been de-
scribed that plasma levels reached in women are higher
than those obtained in men. It is interesting to note that
from 300 new drug applications to FDA from 1995 to
2000, in 163 a gender analysis was included, 11 drugs
showed a difference higher than 40% [45].
In order to contribute to the establishment of gender
differences in the pharmacokinetics, our group evaluated
the oral pharmacokinetics of three drugs, pantoprazole,
levofloxacin and losartan in women and men. In the first
study, oral pharmacokinetics of enteric coated formula-
tion of pantoprazole was evaluated in 52 healthy volun-
teers (26 women and 26 men). It was observed that
higher plasma levels were reached in women, but such
differences dissapeared when data were normalized by
the administered dose (Figure 1); this was reflected in
differences in several pharmacokinetic parameters, Cmax,
AUC and CL/F. When values were normalized by the
body weight of individuals, it can be seen that volume of
distribution is slightly lower in women (Table 2). These
results seem to indicate that volume of distribution is
reduced in about 20% in women than in men, that may
Gender Differences in the Pharmacokinetics of Oral Drugs
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36
(a) (b)
Figure 1. Plasma level-time curves in women (open circles) and men (dark circles) after
administration of a single oral 40 mg pantoprazole dose. A) Raw data and B) normalized
by the dose data (in mg/kg). Data are expressed as mean ± s.e.m.
Table 2. Demographic data and pharmacokinetic parameters of pantoprazole obtained in
women and men after administration of a single 40 mg oral dose. Data are expressed as
mean ± s.e.m. *p 0.05.
Parameter Men Women
Age (years) 21.31 ± 0.47 24.38 ± 1.10*
Height (cm) 167.35 ± 1.19 156.92 ± 0.88*
Weight (kg) 67.39 ± 1.40 57.87 ± 2.42*
Cmax (ng/ml) 3131.15 ± 152.54 3248.70 ± 228.40
NCmax (ng.kg/ml.mg) 5207.21 ± 211.59 4615.56 ± 319.98
tmax (h) 2.88 ± 0.20 2.77 ± 0.21
AUC8h (ng.h/ml) 5455.60 ± 346.21 7190.20 ± 724.26*
NAUC8h (ng.h.kg/ml.mg) 9064.77 ± 512.94 10142.28 ± 977.31
AUC (ng.h/ml) 5787.62 ± 401.24 8015.38 ± 1056.81*
NAUC (ng.h.kg/ml.mg) 9612.61 ± 607.37 11332.01 ± 1432.14
t1/2 (h) 1.26 ± 0.05 1.31 ± 0.13
Vd/F (l) 13.68 ± 0.91 10.69 ± 0.72*
NVd/F (l/kg) 0.202 ± 0.012 0.185 ± 0.011
CL/F (l/h) 7.71 ± 0.52 6.43 ± 0.55
NCL/F (l/h.kg) 0.114 ± 0.007 0.112 ± 0.010
N indicates the normalized values taking into account the dose normalized by the body weight.
be due to differences in the body water between women
and men. In the second study, the oral pharmacokinetics
of levofloxacin was evaluated in 28 women and 27 men.
Figure 2 shows the plasma levels time curve after ad-
ministration of the drug before and after normalization of
the dose by the body weight. It can be seen that plasma
levels reached are about 20% higher in women, but the
difference completely dissapeared when data were nor-
malized by the individuals weight. Pharmacokinetic pa-
rameters (raw and normalized) are given in Table 3. It is
clearly shown that the differences observed with this
drug are exclusively due to the given dose (higher nor-
malized dose is given in women).
In the third study, oral pharmacokinetics of losartan
Gender Differences in the Pharmacokinetics of Oral Drugs
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37
Figure 2. Plasma level-time curves in women (open circles) and men (dark circles) after
administration of a single oral 500 mg levofloxacin dose. (Left) Raw data and (right)
normalized by the dose data (in mg/kg). Data are expressed as mean ± s.e.m.
Table 3. Demographic data and pharmacokinetic parameters of levofloxacin obtained in
women and men after administration of a single 500 mg oral dose. Data are expressed as
mean ± s.e.m. *p < 0.05, **p < 0.0005, #p < 0.0001.
Parameter Men Women
Age (years) 22.52 ± 1.00 25.82 ± 1.35
Height (cm) 168.83 ± 1.47 157.57 ± 1.09*
Weight (kg) 69.11 ± 1.74 56.50 ± 1.25*
Cmax (µg/ml) 8.45 ± 0.45 10.28 ± 0.51 **
NCmax (µg.kg/ml.mg) 1.14 ± 0.05 1.15 ± 0.05
tmax (h) 1.47 ± 0.18 1.89 ± 0.23
AUC (µg.h/ml) 60.75 ± 1.52 72.10 ± 2.38 #
NAUC (µg.h.kg/ml.mg) 8.31 ± 0.19 8.05 ± 0.20
t1/2 (h) 6.37 ± 0.12 5.00 ± 0.08 **
Vd/F (l) 76.75 ± 2.36 51.24 ± 1.56 #
NVd/F (l/kg) 1.116 ± 0.029 0.907 ± 0.020
CL/F (l/h) 8.37 ± 0.21 7.14 ± 0.23 **
NCL/F (l/h.kg) 0.122 ± 0.003 0.126 ± 0.003
N indicates the normalized values taking into account the dose normalized by the body weight.
was evaluated in 26 women and 26 men. Figure 3 shows
the plasma levels time curve after administration of 50
mg of the drug. It can be seen that plasma levels reached
are higher in women than in men. When pharmacokinetic
parameters were normalized by the body weight, an in-
creased clearance was observed in women (Table 4).
Results obtained in these three studies and two other
studies previously reported by our group with flucona-
zole [33] and clindamycin [54] indicate that plasma levels
reached were higher in women, although different meta-
bolic pathways or transporters were involved (CYP3A4,
CYP2C9, CYP2C19, Pgp). One drug that allows to es-
tablish the differences in the distribution of the drug be-
tween men and women is fluconazole [33]. As fluconazole
is widely distributed in total body water (TBW), and, since
men have more content of TBW, volume of distribution
Gender Differences in the Pharmacokinetics of Oral Drugs
Copyright © 2011 SciRes. PP
38
(a) (b)
Figure 3. Plasma level-time curves in women (open circles) and men (dark circles) after
administration of a single oral 50 mg losartan dose. A) Data during the whole sample
time period and B) data in the first 4 hours after losartan administration. Data are ex-
pressed as mean ± s.e.m.
Table 4. Demographic data and pharmacokinetic parameters of losartan obtained in
women and men after administration of a single 50 mg oral dose. Data are expressed as
mean ± s.e.m. *p < 0.01, **p < 0.002, ***p < 0.001.
Parameter Men Women
Age (years) 23.65 ± 0.71 25.46 ± 1.14*
Height (cm) 172.46 ± 1.57 156.81 ± 1.31*
Weight (kg) 70.31 ± 2.11 58.37 ± 2.13***
Cmax (ng/ml) 249.42 ± 24.67 373.14*
NCmax (ng.kg/ml.mg) 343.19 ± 34.43 441.50 ± 56.55
tmax (h) 0.91 ± 0.09 1.02 ± 0.16
AUC24h (ng.h/ml) 445.92 ± 38.51 673.85 ± 50.04***
AUC (ng.h/ml) 522.33 ± 43.74 789.08 ± 64.74**
NAUC (ng.h.kg/ml.mg) 717.02 ± 59.36 923.32 ± 99.05
t1/2 (h) 3.15 ± 0.53 3.89 ± 1.02
Vd/F (l) 441.30 ± 61.60 316.80 ± 44.30
NVd/F (l/kg) 6.2765 ± 0.8761 5.4274 ± 0.7590
CL/F (l/h) 0.91 ± 0.09 1.02 ± 0.16
NCL/F (l/h.kg) 0.0129 ± 0.0013 0.0175 ± 0.0027***
N indicates the normalized values taking into account the dose normalized by the body weight.
was higher in men and therefore, plasma concentrations
were lower than in women. On the other hand, to our
knowledge the only case in which plasma levels reached,
normalized by the dose, are lower in women is with
metronidazole [34], in which increased clearance and
lower half-life was obtained.
As it can be seen, it is not possible to anticipate gen-
der-related differences in the oral pharmacokinetics of
drugs, and therefore, it is important to evaluate case by
case in order to establish the adequate dosage regimen
according to body weight and gender, although in most
of the cases higher levels are reached in women than in
men and such difference is mainly due to the administra-
tion of higher normalized doses in women.
Gender Differences in the Pharmacokinetics of Oral Drugs
Copyright © 2011 SciRes. PP
39
6. Conclusions
There is enough evidence that indicate that gender re-
lated differences in the pharmacokinetics of drugs exist.
In general, higher plasma levels are reached in women
than in men and such differences are mainly due to dif-
ferences in the volume of distribution, due to different
content of body water, and in clearance due to renal flow
and metabolic activity. However, it seems that an impor-
tant contribution for observing higher levels in women is
that usually doses employed in women are higher than in
men when they are normalized by the body weight.
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