K Ravi Sankar1, NL Prasanthi2*, SS
Manikiran2 and N Rama Rao2
1Aurobindo Pharma Ltd., Hyderabad.
2Chalapathi Institute
of Pharmaceutical Sciences, Lam, Guntur- 522034
ABSTRACT:
Roxithromycin, an antibacterial agent is
widely used in
the treatment of various infections. One of the major problem
with this drug is its low solubility in biological fluids. Therefore, solid
dispersions of roxithromycin were prepared using mannitol as
carrier by different techniques like physical mixing,
melting method, melt solvent method, kneading technique and common solvent
method to improve the aqueous solubility. Solid dispersions were prepared in
1:1, 1:2, 1:4 and 1:9 ratios of drug to carrier. Prepared solid
dispersions were evaluated for solubility, content uniformity, dissolution rate
and efficiency. More solubility and faster dissolution was exhibited by solid dispersions containing 1:4 ratio of drug and carrier prepared by melting method. FT-IR
studies revealed the absence of significant drug-carrier interactions.
KEYWORDS:
Roxithromycin, Mannitol, solid dispersions, solubility.
INTRODUCTION:
Aqueous
solubility of a drug can be a critical limitation to its oral absorption. Lipophilic molecules, especially those belonging to the biopharmaceutics
classification system (BCS) class II and IV, dissolve slowly, poorly and
irregularly, and hence pose serious delivery challenges, like incomplete
release from the dosage form, poor bioavailability, increased food effect, and
high inter-patient variability 1. Many solubilization
techniques have been described that either change the nature of the solvent
environment (co-solvent systems, emulsions, micellization)
or the chemical identity of the dissolved solute (salt formation, complexation, pro-drugs)2. Alteration of the
solid state at the particle or molecular level involves a physical change in
the drug and is an attractive option for improving drug solubility 3.
Particle size reduction by micronization or nanonization can enhance the dissolution rate; however, the apparent solubility remains unaltered. At
the molecular level, polymorphs offer a limited solubility advantage because of
a small difference in free energy4. In contrast, amorphous systems
with excess thermodynamic properties and lower energetic barrier can offer
significant solubility benefits. This solubility benefit can be further
enhanced by preparing solid dispersions (SDs). SDs contribute
by slowing devitrification, enhancing wettability and modulating the properties of the solvent 5.
The aim of
the present study was to examine the dissolution properties of SDs of roxithromycin (ROX), prepared
with small molecule such as mannitol. ROX is erythromycin 9-[O-[(2)-methoxyethoxy) methyl] oxime, a
semi synthetic macrolide antibiotic drug, very slightly
soluble in water and aqueous fluids and its absorption is dissolution rate
limited. ROX is used in the treatment of UTI, RTI, ENT, genital tract, skin and
soft tissue infections 6, 7. In the present investigation, several
solid dispersions of ROX were prepared employing physical mixing, melting
method, melt solvent method, kneading method and common solvent method using mannitol which is a highly water soluble carrier. The
prepared solid dispersions were characterized and the dissolution rates were
compared with that of pure drug to evaluate the efficiency of solid dispersions
in improving the dissolution rate.
MATERIALS
AND METHODS:
Materials:
Roxithromycin was obtained from Acta Pharmaceuticals, Warangal. Mannitol
was obtained from BDH chemicals, Mumbai. Mannitol was
obtained from Sd-fine chemicals, Mumbai. All other
ingredients used were of AR grade.
Methods:
Preparation
of solid dispersions8:
Solid dispersions of ROX were prepared using mannitol as a carrier using different preparation
techniques. Drug: carrier ratios of 1:1, 1:2, 1:4 and 1:9 were prepared by the
physical mixing, melting method, melt solvent method, kneading method and
common solvent method.
Physical mixing:
Physical mixtures were prepared by mixing ROX
and mannitol in a glass mortar for three minutes. The
resulting mixture was sieved through # 100 and then stored in a desiccator at room temperature until use.
Melting method:
Solid dispersions were prepared by melting
the physical mixture of ROX and mannitol in a sand
bath. The fusion temperature was controlled between 165-175°C. The molten
mixture was immediately cooled and solidified in an ice bath with vigorous
stirring. The solid obtained was scrapped, crushed, pulverized and passed
through #100. The obtained product was stored in a dessicator.
Melt solvent method:
ROX was dissolved in methanol and the
solution was incorporated into the melt of mannitol
at 165°C by pouring into it. It was kept in an ice bath for sudden cooling. The
mass was kept in a dessicator for complete drying.
The solidified mass was scrapped, crushed, pulverized and passed through #100.
Kneading
method:
ROX was
dissolved in methanol and this solution was added to aqueous solution of mannitol, which was prepared by dissolving mannitol in water. Then the mixture was triturated in a
glass mortar until it was dried. The dried powder was passed through #100 and
the final product was stored in a dessicator.
Common
solvent method:
ROX and
mannitol were taken in a glass mortar and this
mixture was dissolved in methanol. The prepared solution was triturated until
methanol was completely removed. The powder obtained after complete removal of
methanol was passed through #100 and was stored in dessicator.
Solubility studies9:
Solubility
studies of both pure ROX and prepared solid dispersions were carried out by
taking solid dispersions equivalent to 100 mg of ROX into 25ml of distilled
water. The flasks were sealed and shaken 24h at room temperature on a rotary
flask shaker. To get equilibrium the flasks were kept aside for 24h, filtered
through 0.45μm membrane filter and from the filtrate 1 ml of solution was
taken and diluted to 10 ml with 0.1 N HCl. The
samples were analyzed spectrophometrically by using
UV-Visible spectrophotometer at 205nm.
Estimation of ROX10:
Solid dispersions equivalent to 100 mg of ROX
was extracted with 50ml of 0.1 N HCl in a 100 ml
volumetric flask sonicated for 15 min. Then the volume was made up to 100 ml with
distilled water. The mixture was filtered, diluted suitably and the drug
content was measured at 205nm using ELICO-167 double beam UV spectrophotometer.
In vitro dissolution studies:
The in
vitro dissolution studies of ROX in pure form and from various solid
dispersions were performed in USP XXI eight stage dissolution rate test apparatus
employing paddle stirrer. In 900 ml of distilled water, a sample equivalent to
150mg of ROX, a speed of
50rpm and a temperature of 37 ± 0.5°C were employed in each case.
A 5 ml aliquot was withdrawn at predetermined time intervals of 2, 5, 10, 15,
30, 45 and 60 minutes and then 5 ml of fresh dissolution medium was replaced to
maintain the constant volume of dissolution medium. From the samples collected,
1 ml was taken and diluted to 5 ml with 0.1 N HCl and
the absorbance of the diluted solutions was measured at 205 nm using
spectrophotometer against 0.1N HCl as blank. The amount of ROX released was calculated
from the standard graph. The dissolution experiments were conducted in
triplicate.
Khan suggested dissolution efficiency (DE) as
a suitable parameter for the evaluation of in
vitro dissolution data. Dissolution efficiency is defined as the area under
dissolution curve up to a certain time ‘t’ expressed as percentage of the area
of the rectangle described by 100% dissolution in the same time 11.
Infrared spectroscopy:
FT-IR
spectra of pure ROX, pure mannitol and solid
dispersions of ROX:mannitol
1:4 ratio prepared by melting method were obtained by Perkin-Elmer Fourier
transform infrared spectrophotometer using KBr
pellets. KBr pellets were prepared by gently mixing
the sample with KBr (1:100). The scanning range was
2000 to 400cm-1.
Figure
1: Solubility data of roxithromycin and its solid
dispersions
TABLE 1:
FORMULATION OF ROXITHROMYCIN SOLID DISPERSIONS
|
S. No |
Batch
code |
Composition |
Method |
Ratio (Drug
: Carrier) |
|
1 |
F1 |
Roxithromycin + Mannitol |
CSV |
1:1 |
|
2 |
F2 |
Roxithromycin + Mannitol |
CSV |
1:2 |
|
3 |
F3 |
Roxithromycin + Mannitol |
CSV |
1:4 |
|
4 |
F4 |
Roxithromycin + Mannitol |
CSV |
1:9 |
|
5 |
F5 |
Roxithromycin + Mannitol |
KNE |
1:1 |
|
6 |
F6 |
Roxithromycin + Mannitol |
KNE |
1:2 |
|
7 |
F7 |
Roxithromycin + Mannitol |
KNE |
1:4 |
|
8 |
F8 |
Roxithromycin + Mannitol |
KNE |
1:9 |
|
9 |
F9 |
Roxithromycin + Mannitol |
MSV |
1:1 |
|
10 |
F10 |
Roxithromycin + Mannitol |
MSV |
1:2 |
|
11 |
F11 |
Roxithromycin + Mannitol |
MSV |
1:4 |
|
12 |
F12 |
Roxithromycin + Mannitol |
MSV |
1:9 |
|
13 |
F13 |
Roxithromycin + Mannitol |
MLT |
1:1 |
|
14 |
F14 |
Roxithromycin + Mannitol |
MLT |
1:2 |
|
15 |
F15 |
Roxithromycin + Mannitol |
MLT |
1:4 |
|
16 |
F16 |
Roxithromycin + Mannitol |
MLT |
1:9 |
|
17 |
F17 |
Roxithromycin + Mannitol |
PM |
1:1 |
|
18 |
F18 |
Roxithromycin + Mannitol |
PM |
1:2 |
|
19 |
F19 |
Roxithromycin + Mannitol |
PM |
1:4 |
|
20 |
F20 |
Roxithromycin + Mannitol |
PM |
1:9 |
|
CSV: common solvent
method KNE:
kneading technique MSV: melt solvent
method MLT: Melting method PM: Physical mixing |
||||
TABLE 2:
SOLUBILITY PROFILE OF ROXITHROMYCIN SOLID DISPERSIONS
|
S. No |
Batch
code |
Method |
Ratio (Drug
: Carrier) |
Solubility
(μg/ml) |
|
1 |
ROX |
- |
Pure drug |
0.545 |
|
2 |
F1 |
CSV |
1:1 |
0.780 |
|
3 |
F2 |
CSV |
1:2 |
0.935 |
|
4 |
F3 |
CSV |
1:4 |
1.120 |
|
5 |
F4 |
CSV |
1:9 |
1.065 |
|
6 |
F5 |
KNE |
1:1 |
0.715 |
|
7 |
F6 |
KNE |
1:2 |
0.815 |
|
8 |
F7 |
KNE |
1:4 |
0.990 |
|
9 |
F8 |
KNE |
1:9 |
0.950 |
|
10 |
F9 |
MSV |
1:1 |
0.835 |
|
11 |
F10 |
MSV |
1:2 |
1.150 |
|
12 |
F11 |
MSV |
1:4 |
1.430 |
|
13 |
F12 |
MSV |
1:9 |
1.375 |
|
14 |
F13 |
MLT |
1:1 |
1.040 |
|
15 |
F14 |
MLT |
1:2 |
1.265 |
|
16 |
F15 |
MLT |
1:4 |
1.550 |
|
17 |
F16 |
MLT |
1:9 |
1.525 |
|
18 |
F17 |
PM |
1:1 |
0.610 |
|
19 |
F18 |
PM |
1:2 |
0.684 |
|
20 |
F19 |
PM |
1:4 |
0.770 |
|
21 |
F20 |
PM |
1:9 |
0.735 |
Figure 2: In vitro dissolution
profile of solid dispersions of roxithromycin in 1:1
ratio prepared by various methods
Figure 3: In vitro dissolution
profile of solid dispersions of roxithromycin in 1:2 ratio prepared by various methods
Figure 4: In vitro dissolution
profile of solid dispersions of roxithromycin in 1:4 ratio prepared by various methods
TABLE 3:
DISSOLUTION PARAMETERS OF ROXITHROMYCIN SOLID DISPERSIONS
|
Batch
code |
Zero
order ‘r’ value |
First
order ‘r’ value |
Hixson-Crowell
‘r’ value |
K1 (min-1) |
DE30 (%) |
T50 (min) |
|
ROX |
0.986 |
-0.992 |
0.990 |
0.0062 |
19.46 |
111.44 |
|
F1 |
0.915 |
-0.946 |
0.937 |
0.0101 |
35.50 |
68.38 |
|
F2 |
0.920 |
-0.959 |
0.948 |
0.0135 |
42.38 |
51.0 |
|
F3 |
0.942 |
-0.982 |
0.972 |
0.0179 |
47.40 |
38.57 |
|
F4 |
0.951 |
-0.985 |
0.977 |
0.0158 |
43.96 |
43.61 |
|
F5 |
0.980 |
-0.987 |
0.986 |
0.0066 |
21.47 |
103.76 |
|
F6 |
0.944 |
-0.964 |
0.958 |
0.0089 |
30.53 |
77.15 |
|
F7 |
0.927 |
-0.964 |
0.954 |
0.0118 |
38.74 |
57.86 |
|
F8 |
0.975 |
-0.987 |
0.985 |
0.0119 |
33.22 |
57.86 |
|
F9 |
0.926 |
-0.967 |
0.958 |
0.0112 |
37.08 |
61.41 |
|
F10 |
0.914 |
-0.963 |
0.949 |
0.0186 |
47.04 |
39.07 |
|
F11 |
0.950 |
-0.989 |
0.975 |
0.0267 |
53.89 |
25.94 |
|
F12 |
0.947 |
-0.992 |
0.983 |
0.0248 |
54.53 |
27.86 |
|
F13 |
0.928 |
-0.970 |
0.961 |
0.0126 |
38.89 |
54.71 |
|
F14 |
0.946 |
-0.985 |
0.975 |
0.0177 |
51.60 |
37.14 |
|
F15 |
0.949 |
-0.965 |
0.978 |
0.0085 |
58.88 |
21.64 |
|
F16 |
0.946 |
-0.983 |
0.982 |
0.0294 |
58.33 |
23.5 |
|
F17 |
0.982 |
-0.988 |
0.987 |
0.0064 |
20.58 |
107.49 |
|
F18 |
0.971 |
-0.982 |
0.979 |
0.0078 |
25.63 |
88.5 |
|
F19 |
0.873 |
-0.906 |
0.985 |
0.0320 |
34.10 |
81.32 |
|
F20 |
0.917 |
-0.941 |
0.934 |
0.0082 |
30.56 |
83.58 |
RESULTS AND
DISCUSSION:
Solid
dispersions of ROX were prepared by physical
mixing, melting method, melt solvent method, kneading technique and common
solvent method using mannitol as a carrier in
different drug, carrier ratios of 1:1, 1:2, 1:4 and 1:9. In the present work,
total twenty formulations were prepared and their complete composition is shown
in Table 1. All the solid dispersions obtained were fine and having good flow
properties. Solubility profile of ROX from physical mixture and solid
dispersion in water is shown in Table 2 and in Figure 1. The results of the
solubility studies revealed that all solid dispersions have shown increase in
solubility compared to that of pure ROX. The amount of mannitol
was increased, the solubility of ROX was increased.
Solid dispersions of ROX: mannitol in 1:4 ratio
prepared by melt method has shown highest improvement in solubility. Initially
the solubility is increased due to the release of the drug from the molecular
dispersion of drug in the carrier molecule. As the concentration of mannitol is further increased, the solubility is decreased
due to the distortion of the molecular aggregate structure between the drug and
carrier. Such distortion can release more and more carrier molecules into the
bulk, which eventually prevents further solubility of the drug. The distortion
of the molecular dispersion structure leaves an insoluble base particle and
increased accumulation of carrier molecule in the bulk seems to cause a
saturation by which further solubility is retarded. The solid dispersion of
ROX: mannitol 1:9 ratio has exhibited this negative
effect. The drug content of all the prepared solid dispersions was found to be
within the limits.
The dissolution rate of ROX from various
solid dispersions was studied in distilled water. The dissolution of ROX from
all the solid dispersions was rapid and more than the pure drug. The
dissolution data was fitted into zero order, first order and Hixson-crowell’s cube root models to asses
the kinetics and mechanism of dissolution. The model that gave higher ‘r’ value
was considered as the best fit model. The ‘r’ values were found to be higher in
the first order model than zero order. DE30 values were calculated
in each case as per Khan et.al. Only 33.67% of ROX dissolved in 60min giving the
slowest dissolution rate in the case of pure drug this may be due to
hydrophobic property of the powder. The increase in dissolution rate from solid
dispersions may be due to molecular level dispersions of drug in solid
dispersions. The dissolution rate of ROX in solid dispersions was strongly
depends upon the relative concentration of the drug to carrier ratio and method
of preparation. Table 3 enlists the dissolution parameters of ROX solid
dispersions prepared by various methods. Solid dispersions formulated with all
the methods exhibited significant improvement in the dissolution parameters of
ROX. The increase in dissolution rate is in the order of melting method >
melt solvent method > common solvent method > kneading method > physical mixing. The dissolution data is
shown in the Figures 2, 3, 4 and 5. From all the formulations, the maximum
dissolution was documented for the drug to the carrier ratio of 1:4.
Figure
5: In vitro dissolution profile of
solid dispersions of roxithromycin in 1:9 ratio prepared by various methods
From
the IR spectrum of pure ROX, a characteristic peak was observed at
approximately 1750 cm-1. Form the IR spectrum of pure mannitol, characteristic peaks were observed between 1000
cm-1 and 1050 cm-1. From the IR spectrum of the solid
dispersion, it was found that the characteristic peaks of ROX and pure mannitol were observed at the same place without any
change. It was concluded that there was no interaction between ROX and mannitol.
ACKNOWLEDGEMENTS:
The authors are thankful to Chalapathi Educational Society, Guntur for providing the
necessary facilities.
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Received on 02.01.2010
Accepted on 22.02.2010
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Research
Journal of Pharmaceutical Dosage Forms and Technology. 2(2): March –April. 2010,
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