JO U R N A L O F
J. Vet. Sci. (2009), 10(4), 293?297
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Modification of pharmacokinetics of norfloxacin following oral
administration of curcumin in rabbits
B. H. Pavithra1, N. Prakash1,*, K. Jayakumar2
1Department of Pharmacology and Toxicology, Veterinary College, Karnataka Veterinary, Animal & Fishery Sciences
University, Postbox No.6, Bidar-585 401, India
2Department of Pharmacology & Toxicology, Veterinary College, Hebbal Campus, Bangalore-560 024, India
Investigation was carried out in adult New Zealand white
rabbits to study the influence of curcumin pre-treatment
on pharmacokinetic disposition of norfloxacin following
single oral administration. Sixteen rabbits were divided
into two groups of eight each consisting of either sex.
Animals in group-I were administered norfloxacin (100
mg/kg body weight p.o), while animals in group-II received
similar dose of norfloxacin after pre-treatment with
curcumin (60 mg/kg body weight per day, 3 days, p.o).
Blood samples were drawn from the marginal ear vein into
heparin-coated vials at 0 (zero time), 5, 10, 15, 30 min and
1, 2, 4, 6, 12 and 24 h post-treatment. Plasma norfloxacin
concentrations were determined by high performance
liquid chromatography. The plasma concentration-time
profile of norfloxacin was adequately described by a one-
compartment open model. The pharmacokinetic data
revealed that curcumin-treated animals had significantly
(p ≤ ≤ 0.05) higher area under the plasma concentration-
time curve and area under the first moment of plasma
drug concentration-time curve. Prior treatment of curcumin
significantly (p ≤ ≤ 0.05) increased elimination half-life and
volume of distribution of norfloxacin. Further treatment
with curcumin reduced loading and maintenance doses by
26% and 24% respectively.
Keywords: curcuma longa, norfloxacin, oral administration,
Norfloxacin is a member of the fluoroquinolone group of
antimicrobial agents. It has a wide spectrum of activity,
excellent tissue penetration and is rapidly bactericidal at
low concentrations. Norfloxacin has a minimum inhibitory
concentration (MIC90) of 0.06, 0.12, 0.25 and 0.5 mg/mL
for Haemophilus influenzae, Escherichia coli, Enterobacter
spp. and Klebsiella spp., respectively . This antibiotic
shows promise as an antimicrobial agent for bacterial
diseases of the respiratory, genito-urinary and gastro-
intestinal tracts . Encouraging results have been
observed following the therapeutic use of norfloxacin in
dogs suffering from hemorrhagic gastroenteritis caused by
E. coli, Salmonella spp., and Shigella spp. , and norfloxacin
has been successfully employed to treat genital tract
infections caused by Pseudomonas aeruginosa in bulls
. The absolute bioavailability of norfloxacin in humans
and in laboratory animals is reported to be 40% , while
in most domestic species the per-os bioavailability varies
between 30∼40% .
Turmeric (Curcuma longa) is a medicinal plant extensively
used in Ayurveda, Unani and Siddha medicine as a home
remedy for various diseases. Curcumin, which is the active
component of Curcuma longa, improves the per-os
bioavailability of the immunosuppressive agent mylophenolic
acid by inhibiting non-specific drug metabolizing enzymes
. Similarly, curcumin suppresses drug metabolizing
enzymes (CYP3A4) in the liver  as well as inducing
changes in the drug transporter P-glycoprotein, hence
increasing the maximum absorption concentration (Cmax)
and area under the plasma concentration-time curve
(AUC) of celiprolol and midazolam in rats . With this
background, the present study was undertaken to evaluate
the influence of curcumin pre-treatment on the disposition
kinetics of norfloxacin and to assess its impact on dosage
regimen in rabbits.
Materials and Methods
The study was conducted in New Zealand white rabbits
weighing 1.65 ± 0.22 kg, divided into two groups with
eight rabbits in each group. The rabbits were acclimatized
for three weeks to laboratory conditions before initiating
294 B. H. Pavithra et al.
Table 1. Comparison of mean plasma levels of norfloxacin
(mg/mL) at different time intervals following oral administration
in control (Group-I) and curcumin treated (Group-II) rabbits
Time (h)Group-I Group-II
0.37 ± 0.05
0.46 ± 0.04
2.23 ± 0.08
1.50 ± 0.25
0.62 ± 0.01
0.48 ± 0.03
0.41 ± 0.01
0.37 ± 0.01
0.17 ± 0.04
0.01 ± 0.001
0.50 ± 0.25*
2.87 ± 0.17*
1.19 ± 0.01*
1.08 ± 0.03
0.84 ± 0.01*
0.59 ± 0.01*
0.32 ± 0.03
0.21 ± 0.06
0.13 ± 0.01
0.09 ± 0.01*
0.07 ± 0.02
*p ≤ 0.05, ND = Not detected. Data are presented as mean ± SE.
the experiment. They were housed in individual cages and
fed with antibiotic free diet. Feed and water were provided
ad libitum. Feed was withheld for at least 6∼8 h before and
until 4 h after drug administration. Necessary approval
from the Institutional Animal Ethics Committee was
obtained to carry out the investigation.
Norfloxacin (Aravind Pharma, India) was dissolved in
0.1 N HCl to obtain a 3.33% solution (50 mg of norfloxacin
in 1.5 mL 0.1 N HCl). The required amount of curcumin
(Sigma-Aldrich, USA) was dissolved in a mixture of
distilled water and Tween-20 at a 2 : 1 ratio restricting the
total volume to 4∼5 mL. Group-I rabbits (control) received
norfloxacin at the rate of 100 mg/kg body weight as a single
oral dose. The rabbits in group-II were administered a
similar dose of norfloxacin after pre-treatment with
curcumin (60 mg/kg body weight; p.o) for three days at an
interval of 24 h. Blood samples (1.0∼1.5 mL) were aseptically
drawn from the marginal ear vein into heparin-coated tubes
(Hi-Media, India) immediately before (0) at 5, 10, 15 and
30 min, and 1, 2, 4, 6, 8, 12 and 24 h after the administration
of norfloxacin. Plasma samples were obtained by
centrifugation of each blood sample (1,250 ×g, 10 min) and
were stored at ?20oC (for not more than 24 h) until being
Plasma norfloxacin concentrations were determined
using high performance liquid chromatography (HPLC;
Shimadzu, Japan). Dilutions of norfloxacin (E. Merck,
India) ranging from 0.01∼4 mg/mL were carried out with the
mobile phase to obtain a standard curve. The HPLC system
consisted of double pump (LC-20AT), rheodyne manual
injector with 20 μL loop, dual wavelength ultraviolet
detector (SPD-20A) and LC Solution software for data
analysis. Chromatography was carried out using a reverse
phase C18 column (250 × 4.5 mm, particle size 5 ± 0.3 μm,
pore diameter 100 ± 10 Ao; Phenomenax, USA) as a
stationary phase. The mobile phase consisted of 0.1% v/v
orthophosphoric acid (pH adjusted to 2.0) and acetonitrile
mixed at a v/v ratio of 850 : 150. Chromatography was
carried out at a flow rate of 1 mL/min at room temperature
and the absorbance of norfloxacin at 275 nm was
measured. The cleaned-up plasma samples  were
analyzed for 8 min; there were no interfering peaks in the
chromatogram at the retention time (Rt = 4.90 ± 0.14 min)
of norfloxacin. The quantification limit was 0.015 μg/mL
and the standard curve was linear in the range 0.015∼4
μg/mL with a R2 value of 0.999. Extraction recovery was
determined to be 94.17% by comparing peak areas
obtained for plasma-based standards and those obtained
for mobile phase-based standards. The intra- and inter-day
assay coefficients of variations were ＜ 8.0%.
The plasma concentration-time profile of norfloxacin of
each experimental animal was used to determine its
pharmacokinetics. The pharmacokinetic data of norfloxacin
was analyzed using the ‘method of least square’ and
‘method of residual yields’ . The compartmental analysis
of the data was undertaken using the mono-exponential
p = Be?βt ? Ae?Kat
intercept of regression line of elimination phase, A is the
zero-time plasma drug concentration intercept of regression
line of absorption phase, Ka is the absorption rate constant,
β is the overall elimination rate constant, t is the time and
e is the natural logarithm base.
The total AUC and area under the first moment of plasma
drug concentration-time curve (AUMC) were calculated
as described previously . The volume of distribution
(Vd(area)) and clearance from the body (ClB) were calculated
as previously described  for a non-vascular route of
The loading and maintenance dosage schedules were
selected to maintain a MIC of 0.1, 0.5 and 1.0 μg/mL in
The difference between the means of the two treatments
was determined by student’s t-test  and the data were
analyzed using GraphPad Instant software (GraphPad
p = plasma drug concentration, B is the zero-time
The mean plasma concentration of norfloxacin was
significantly (p ≤ 0.05) higher in curcumin pre-treated
rabbits, although such effect was not observed during the
entire period of absorption phase (Table 1, Fig. 1). The
plasma concentration of norfloxacin persisted up to 24 h in
Modification of pharmacokinetics of norfloxacin following oral administration of curcumin in rabbits 295
Fig. 1. Semilogarithmic plot of plasma concentration-time
profile of norfloxacin in control (Group-I) and curcumin treated
(Group-II) rabbits following single oral dose administration.
Table 2. Comparative pharmacokinetics of orally administered
norfloxacin (100 mg/kg body weight) in control (Group-I) and
curcumin treated (Group-II) rabbits
Parameter Unit Group-IGroup-II
1.84 ± 0.03
1.95 ± 0.14
0.278 ± 0.01
1.04 ± 0.01
0.35 ± 0.01
2.49 ± 0.13
2.67 ± 0.42
13.40 ± 1.62
5.01 ± 0.19
5.69 ± 0.28
1.49 ± 0.11
27.72 ± 6.22
2.59 ± 0.62*
1.85 ± 1.15
0.231 ± 0.03*
1.11 ± 0.02
0.27 ± 0.06*
2.96 ± 0.34*
4.06 ± 1.24*
22.64 ± 6.34*
5.60 ± 0.15*
7.45 ± 1.70*
1.58 ± 0.03
29.58 ± 3.84*
*p ≤ 0.05. ka: absorption rate constant, A: zero time plasma drug
concentration intercept of regression line of absorption phase, β:
overall elimination rate constant, B: zero time intercept of regression
of elimination phase, t½Ka: absorption half-life, t½β: elimination
half-life, AUC: area under the plasma concentration-time curve,
AUMC: area under first moment of plasma drug concentration-time
curve, MRT: mean residence time, Vd(area): apparent volume of
distribution, ClB: total body clearance of drug, td: total duration of
pharmacological effect. Data are presented as mean ±SE.
Table 3. Dosage regimen of norfloxacin, calculated on the basis of pharmacokinetics values of obtained following oral administration
of curcumin treated (Group-II) and control (Group-I) rabbits at various dosage intervals for microorganisms of different susceptibilities
6 h 8 h12 h6 h 8 h12 h
*Values given are expressed as μg/mL. †Values given are expressed as mg/kg body weight. ‡Values given are loading doses and the values in
parenthesis are maintenance doses.
curcumin-treated rabbits, while it was detected up to 12 h
in the untreated control group (Table 1). The absorption
rate constant and absorption half-life revealed a significant
(p ≤ 0.05) change (Table 2). Prior administration of
curcumin modified the kinetic profile of norfloxacin as
evidenced by the higher AUC, AUMC and mean resident
time. Prior administration of curcumin significantly (p ≤
0.05) reduced the elimination rate constant (β) and
consequently increased the half-life of norfloxacin.
Similarly, there was a significant increase in Vd(area) of
norfloxacin in curcumin-treated rabbits when compared to
untreated controls (Table 2). Prior treatment with curcumin
reduced both loading and maintenance doses up to 26.0%
and 24.0%, respectively, at different norfloxacin MICs
Norfloxacin has antimicrobial activity against a wide
range of bacteria and is being effectively used to treat
respiratory, urinary and gastro-intestinal tract infections in
man and animals. Pharmacokinetic studies on norfloxacin
in rabbits are limited [14,19]. The absorption of norfloxacin
from gastrointestinal tract is limited [5,9]. Curcumin, a
flavonoid isolated from Curcuma longa, improves the
therapeutic concentrations of co-administered drugs [4,24].
With this background, the present study was undertaken to
examine the influence of curcumin on the disposition
profile of norfloxacin in rabbits after oral administration.
The disposition of norfloxacin after a single oral dose
296 B. H. Pavithra et al.
(100 mg/kg body weight) was examined in rabbits with or
without prior exposure to curcumin. A similar dose (per os)
has been used to describe plasma and tissue concentration
of norfloxacin in rabbits . The observed plasma
concentration-time profile of norfloxacin was best described
by the one compartment open model. The plasma levels of
norfloxacin (group-I) at different time intervals were
comparable to previous studies in rabbits receiving a similar
dose , however, the plasma half-life was relatively short
. The increased plasma levels of norfloxacin observed
in the present study (group-II) may be due to the by-pass of
glucuronidation process in the intestine since curcumin
was reported to suppress UDP-glucuronyltransferase levels
in intestine and hepatic tissue . Furthermore, the ability
of curcumin to suppress CYP3A4 drug metabolizing enzymes
 might have delayed the excretion of norfloxacin. It is
more likely that the increased absorption observed in the
present study may have been due to the ability of curcumin
to influence drug transporter protein (P-gp) in the intestine,
as occurs with celiprolol . Similarly, curcumin and
gingerol (from ginger) were observed to inhibit P-gp
mediated 3H-digoxin transport in L-MDR 1 and caco-2
cells in vitro . Furthermore, the modification of
physiological activity in the gastrointestinal tract by
curcumin [3,17] in the group-II rabbits might have
contributed to the improved absorption of norfloxacin.
Norfloxacin undergoes extensive metabolism in the liver
involving both Phase-I and Phase-II . The significantly
higher values of AUC, AUMC and mean residence time
(MRT) observed in the present study might be attributable
to the enhanced systemic availability of norfloxacin
consequent to inhibition of enzymes mostly concerned
with the hepatic metabolism of norfloxacin. Furthermore,
in contrast to the fact that curcumin can induce hepatic
glucuronyltransferase, its suppression at a higher dose
cannot be ruled out. It is noteworthy that curcumin is itself
metabolized through hepatocytes as glucuronides of
tetrahydrocurcumin  and, therefore, the metabolism of
norfloxacin may be delayed due to competition between
The higher plasma elimination half life (t1/2β) of 2.96 ±
0.34 h in the curcumin-treated group when compared to the
control group could be due to prolonged persistence of the
drug in the body due to inhibition of one or more enzyme(s)
concerned with metabolism of norfloxacin. A significant
amount of norfloxacin was excreted unchanged via renal
mechanisms . Therefore, it can be hypothesized that
curcumin might have delayed the excretory mechanism of
norfloxacin, since P-gp protein also exists in the proximal
From a practical point of view, a dosage regimen of 80
and 77 mg/kg of norfloxacin alone or 60 and 55 mg/kg of
norfloxacin after curcumin pre-treatment as the loading
and maintenance dose, respectively, at a 12 h interval
adequately maintains optimal therapeutic concentration of
0.5 μg/mL plasma against resistant pathogens infecting
rabbits. The reduction in the loading and maintenance
doses indicates that prior administration of curcumin is of
economic significance as well as being capable of reducing
side effects, as a lesser amount of drug would be required.
The bioenhancer nature of curcumin is comparable to
piperine , an alkaloid obtained from Piper longum.
Thus, bioenhancer properties of curcumin can be clinically
exploited after appropriate dose titration studies.
The authors are thankful to the Dean of the Veterinary
College, Karnataka Animal, Veterinary and Fishery
Sciences University, Bidar, for providing the necessary
facilities to carry out the investigation.
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