Department of Pharmaceutics, Bharati Vidyapeeth College of
Pharmacy, Kolhapur, Maharashtra, India.
ABSTRACT
In the present study we investigated the
effect of generation 3 (G3) PAMAM dendrimer on the
aqueous solubility of aceclofenac. The aqueous
solubility of aceclofenac was measured in the
presence of dendrimer. A 32 full factorial
design was employed. The concentration of dendrimer
and temperature were used as independent variables, while solubility of drug
was selected as dependent variable. The experimental results showed that the
aqueous solubility of aceclofenac was directly
proportional to concentration of dendrimer and
inversely proportional to the temperature under the experiment performed. Under
the suitable condition, the solubility of aceclofenac
can improves with the PAMAM dendrimer.
KEYWORDS: Dendrimers,
G3 PAMAM dendrimer, 32 full factorial
design, Solubility enhancement.
1. INTRODUCTION
Dendrimer,
also called arborols or
cascade molecules1 or artificial proteins2, is
derived from the Greek words dendron (tree)
and meros (part) 3. They are monodisperse, well-defined artificial macromolecules
which have highly branched, three-dimensional features that resemble the architecture
of a tree, having defined molecular weight and
host-guest entrapment properties4. The
highly branched molecular structure of dendrimers,
which resembles Christmas stars, ice crystals, or treetops5. A typical dendrimer consists of three
basic components (Figure 1): a central
core from which the polymeric branches emanate; repeat units the nature of which determines the microenvironment
of the interior and in turn the solubilization
ability of the dendrimer; and the terminal surface groups, the nature
and number of these groups are mostly responsible for the performance of dendrimers in solution6. The
branched units are prearranged
in layers called ‘‘generations’’ and correspond to the repeating monomer unit
of these macromolecules3.
Dendrimers
are divided into two families, compact and extended dendrimers7.
They are prepared through divergent or convergent iterative procedures to
obtained different sizes or generations8. Polyamidoamine
(PAMAM) dendrimers are founded on an ethylenediamine core, and branched units are constructed
from methyl acrylate and ethylenediamine6.
PAMAM dendrimers are biocompatible, nonimmunogenic water-soluble, and possess terminal
modifiable amine functional groups for binding various guest molecules9.
Hydrophobic drugs can be interacted with the dendrimer
to make them water10. Drugs can either be
attached to dendrimers end groups or encapsulated in
the macromolecule interior11. The high density of amino groups and special structure in PAMAM dendrimers may be projected to have potential applications
in enhancing the solubility of the low aqueous soluble drugs12.
Aceclofenac, a phenylacetic acid derivative, non-steroidal anti-inflammatory drug (NSAID), used in the management of osteoarthritis, rheumatoid
arthritis, and ankylosing spondylitis. Though, the use of such drugs is restricted by their significant
toxicity. The commonest adverse
effects of NSAIDs are usually gastrointestinal disturbances13, such
as gastrointestinal discomfort, nausea, and diarrhoea. It is clear that usually most NSAIDs can damage the esophagus,
stomach, duodenum, small intestine and large intestine14.
Fig. 1: Structure of Dendrimer
It was suggested that the use of
NSAIDs in parenteral could control these proven side
effects. But due to poor aqueous solubility
of NSAIDs, their use in topical and parenteral
formulation has also been limited. The
poor aqueous solubility of drug is generally related to a low bioavailability,
so it needs to increase the aqueous solubility of such drugs15.
The solubility of Nifedipine9, Ibuprofen16,
nicotinic acid17, ketoprofen18, furosemide19
has been tested with dendrimer. In
the present study we investigated the effect of concentration of G3 PAMAM dendrimer and temperature to increase the solubility of
hydrophobic drug, aceclofenac.
MATERIALS AND METHODS:
Materials:
Aceclofenac was a
gift sample from Rantus Pharma
Pvt Ltd. (Hyderabad, India). G3 PAMAM dendrimer
was a gift sample from Dendritech Inc. (USA). All
other ingredients used were of pharmaceutical grade.
Methods:
Solubility testing experiments:
The solubility of aceclofenac in G3
PAMAM dendrimer solutions in 1, 2 and 3 % w/v was
determined at constant neutral pH. Excess ibuprofen was added to 10 ml vials
containing 5 ml of each test solution. The vials were then incubated in an
orbital shaking incubator for 24 h. Then the solutions were filtered through a
0.45 µm filter (Sartorius) and the amount of aceclofenac
in the filtrate determined by UV spectrophotometer at 245 nm. The effect of
temperature on solubility was examined over the range 25, 37 and 45°C.
Fig.2: Response surface plot
Table 1: Full factorial experimental
design layout
Trials
|
Variable level in coded form |
|
|
X1 |
X2 |
|
|
1 |
-1 |
-1 |
|
2 |
-1 |
0 |
|
3 |
-1 |
1 |
|
4 |
0 |
-1 |
|
5 |
0 |
0 |
|
6 |
0 |
1 |
|
7 |
1 |
-1 |
|
8 |
1 |
0 |
|
9 |
1 |
1 |
Factorial Design:
A 32
full-factorial design was constructed to study the effect of dendrimer and temperature on the solubility of drug. In
this study, two factors were evaluated, each at three levels; experimental
trials were performed at all 9 possible combinations (Table 1). The percentage
of G3 dendrimer (X1)
and temperature (X2) were
selected as independent variables. The solubility of drug was selected as
dependent variable. The data were subjected to 3-D response surface methodology
in PCP Disso 2.08 to determine the effect of dendrimer
and temperature on the solubility of drug, dependent variable. The values of
variables in a 32 factorial design are indicated in Table 2. A
statistical model incorporating interactive and polynomial terms was used to
calculate the responses.
Y = bo
+ b1X1 + b2X2 + b12X1X2
+ b11X12 + b22X22……..(1)
Where, Y is the dependent variable, bo
is the arithmetic mean response of the 9 trials, and bi (b1,
b2, b12, b11 and b22)
is the estimated coefficient for the corresponding factor Xi
(X1, X2, X1X2,
X12 and X22), which represents the average
result of changing 1 factor at a time from its low to high value. The
interaction term (X1X2) shows how the
response changes when 2 factors are simultaneously changed. The polynomial
terms (X12 and X22)
are included to investigate the nonlinearity.
Table 2: Values
Amount of Variables in a 32 Factorial Design
Coded Values
|
Actual
Values |
|
|
X1
= Dendrimer Solution % (w/v) |
X2
= Temperature (ºC) |
|
|
-1 |
1 |
25 |
|
0 |
2 |
37 |
|
1 |
3 |
45 |
Table
3: Result of Solubility testing
|
Trials |
Solubility (mg/ml) |
|
8.37 |
|
|
2 |
7.53 |
|
3 |
6.72 |
|
4 |
15.76 |
|
5 |
13.52 |
|
6 |
10.43 |
|
7 |
17.12 |
|
8 |
14.08 |
|
9 |
12.11 |
RESULTS:
Solubility testing:
The solubility experiments
of aceclofenac were carried out using G3 PAMAM dendrimer of molecular weight 6,909 Dalton and 32 amine
groups on the exterior of molecules, and the results were shown in Table 3. It
was observed that the solubility of aceclofenac
increased considerably with PAMAM concentrations. In the presence of G3 PAMAM dendrimer at a fixed pH state, the solubility of aceclofenac in the dendrimer
solutions increased with an increase in
dendrimer concentration. Fig. 2 shows that the amount of aceclofenac dissolved in G3 PAMAM dendrimers
was inversely proportional to the temperature. The cause of this effect is not
clear.
Factorial Design:
The solubility of drug
for the 9 trials showed a wide variation (i.e., from 6.72 to 17.12 mg/ml). The
response of various trials according to the 32 factorial designs
shown in Table 3.
The data clearly imply that the solubility
of drug is effectively dependent on the chosen independent variables.
The fitted equations relating the response to the transformed factor shown in
equation 2.
Final Equation in Terms of Coded
values:
Y = 13.2367 + 3.4483 X1
– 1.9983 X2
– 2.2483 X12
.. (2)
Fig. 2 shows the plot of the percentage of G3 dendrimer
(X1) and the temperature (X2) vs
solubility (mg/ml). The response surface plot was drawn using PCP Disso V 2.08.
The data demonstrate that both X1
and X2 affect the drug
solubility. It is concluded that a maximum concentration of dendrimer
at low temperature favors the significant improvement of solubility of drug.
DISCUSSION:
The G3 PAMAM dendrimers have the ability to significantly enhance the
solubility of poorly water-soluble drug, aceclofenac.
These may be due to the interactions between the surface amine groups of dendrimer molecule and the carboxyl group of aceclofenac. The drug solubility is directly proportional
to the concentration of the dendrimer, this was most
probably due to the increase in the number of surface amines that are available
to interact electrostatically with aceclofenac molecules, and inversely proportional to the
temperature.
ACKNOWLEDGEMENT:
We are thankful to Rantus
Pharma Pvt. Ltd. (Hyderabad,
India) for providing gift sample of aceclofenac.
We are grateful to Dendritech Inc. (USA) for the gift sample of dendrimer.
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Received on
06.03.2009
Accepted on
12.08.2009
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Research
Journal of Pharmaceutical Dosage Forms and Technology. 1(2): Sept.-Oct. 2009,
94-96