INTRODUCTION:

Sustained release drug delivery systems for oral dosing are effective in achieving optimal therapy with drugs that have a narrow therapeutic range of blood concentration or eliminate rapidly. Sustained release dosage forms are designed to bring the blood level of a drug immediately to therapeutic concentration by means of an initial loading dose and then sustains this level for certain predetermined time with maintenance dose. Sustained release drug delivery system, releases drug at very slow rate over an extended period of time. Sustained release oral dosage forms have become more important in therapy as a mean of reduced dosing frequency, hence potentially improving patient compliance and consequently efficacy.¹

Orally administered NSAIDs play an important role in symptomatic management of osteoarthritis, rheumatoid arthritis, anlkylosing spondylitis and other acute painful conditions.

Aceclofenac {2-[(2, 6-Dichlorophenylamino) phenyl] acetoxyacetic acid} is a non-steroidal drug having potent analgesic, anti-inflammatory and antipyretic activities due to its prostaglandin synthatase inhibitory action. It is a newer derivative of diclofenac and has unpleasant taste and causes less gastric irritation. It is mainly absorbed from gastrointestinal tract. It has a pKa value 4.7 so it is practically insoluble in acidic media and soluble in intestinal fluid. Also it has an excretion half life about 4 hrs and 100 % bioavailability. Hence aceclofenac is an ideal candidate to formulate as sustained release dosage form.^2-3

In the present study matrix tablets were prepared by direct compression method, because it requires less time and energy consumption as compare to wet granulation method. The hydrophilic polymers such as xanthan gum, guar gum and HPMC K4M were used. These polymers are nontoxic, easily compressible, good swelling properties and easily available.⁴ Natural gums like xanthan gum and guar gum are the most popular hydrophilic polymers because of their flexibility, cost-effectiveness and broad regulatory acceptance.⁵ PEG 6000 was used as drug release modifier and directly compressible MCC i.e. Avicel pH 102 was used as diluent.

Figure 1. IR spectra of aceclofenac and different polymers (A-B, C-D)

A indicate aceclofenac; B indicate aceclofenac +xanthan gum; C indicate aceclofenac +xanthan gum +guar gum; D indicate aceclofenac+ guar gum +HPMC K4M

The main objective of present study was to formulate and evaluate the once daily sustained release matrix tablet of aceclofenac for effective treatment of rheumatoid arthritis, osteoarthritis, ankylosing spondylitis and other painful conditions.

MATERIALS AND METHODS:

Materials:

Aceclofenac was obtained as generous gift sample from Alembic Pharmaceutical Ltd (Baroda, India). Xanthan gum (viscosity of 1% aqueous solution is 1350 cps at 25⁰C) andguar gum (viscosity of 1% aqueous dispersion is 86 cps at 25⁰C) were obtained as kind gift samples from Alkem (Navi Mumbai, India). HPMC K4M was obtained as a gift from Colorcon (Mumbai, India). Microcrystalline cellulose (MCC; Avicel PH102) and Magnesium stearate was purchased from SD Fines (Mumbai, India). All reagents are analytical grades.

Methods:

Solubility Studies of Aceclofenac:

An excess amount of aceclofenac was taken in 10 ml of different solutions into a mechanical shaker (Orbital shaking incubator, Remi instrument) up to 24 hrs at room temperature. Samples were withdrawn and filtered through a millipore filter Nylon 66 (pore size 0.45 mm) and the amount of drug dissolved was analyzed at 275 nm spectrophotometrically (UV-1700, Shimadzu).

Drug–Excipients Interaction Study:

Thin Layer Chromatography:

Drug-excipient interaction study was done by TLC. Vials were previously washed in water and then with acetone. Physical mixture of drug and excipient was filled in the vials then sealed. The sealed vials were kept at 37 ± 0.5⁰C and 75 % RH for 28 days in programmable environmental test chamber (Remi Lab, Mumbai). Aluminium backed silica gel 60 F₂₅₄ HPTLC plates (10 cm × 20 cm, layer thickness 0.2 mm, E – Merck, Darmstadt, Germany) prewashed with methanol was used for the study. Mobile phase system for aceclofenac (Benzene: Ethyl acetate [2:1]) were used. R_f of drug, excipients and their mixture was determined.

FTIR Spectra:

Infrared (IR) spectroscopy was conducted using a spectrophotometer (Shimadzu FTIR 8400). Spectrum was recorded in the wavelength region of 4000 to 400 cm^-1.The procedure consisted of dispersing sample (drug alone and mixture of drug and excipients) in KBr and compressed into discs by applying a pressure of 5 tons/5 min. Drug and KBr (1:100) and Drug: polymers: KBr (1:1:100) was taken and pellet was prepared using hydraulic press.

DSC Study:

Differential scanning calorimetry was performed using DSC calorimeter (Perkin Ellmer Cyris-DSC). Indium was used as standard to calibrate the DSC temperature and enthalpy scale. The samples (drug alone or mixture of drug and excipients) were heated in sealed aluminum pans under nitrogen flow (30 ml/min) at a scanning rate of 5⁰C/min from 24±1 to 250⁰C. Empty pan was used as a reference. The heat flow as a function of temperature was measured for the drug and drug-polymer mixture.

Evaluation of Precompression Parameters of Sustained Release Tablets:

Angle of Repose:⁶

The angle of repose of powder blends of all batches were determined by fixed funnel method. The accurately weighed powder blends was taken in a funnel. The height of the funnel was adjusted in such a way that the tip of funnel just touches the apex of the heap of the blend. The blend was allowed to flow through the funnel freely onto the surface. The height and diameter of powder cone was measured and angle of repose was calculated using the following equation.

Where, h and r are the height and radius of the powder cone respectively.

TableI: Composition of Aceclofenac Sustained Release Tablet*

Sr. No	Ingredients	A	B	C	F1	F2	F3	T1	T2	T3	T4
1	Aceclofenac	200	200	200	200	200	200	200	200	200	200
2	Xanthan Gum	28	24	24	25	12	12	-	-	-	-
3	Guar Gum	-	-	-	5	4	4	10	8	8	10
4	HPMC K4M	-	-	-	-	-	-	70	30	40	30
5	MCC	168	132	127	126	145	130	76	118	103	111
6	PEG 6000	-	40	45	40	35	50	40	40	45	45
8	MS	4	4	4	4	4	4	4	4	4	4

*Each value represented in mg; HPMC, indicate hydroxypropyl methylcellulose; MCC, indicate microcrystalline cellulose; MS, indicate Magnesium stearate

Table II: Solubility of Aceclofenac in different media

Solution	Solubility (mg/ml)
Dist water	0.082±0.015
0.1N HCl or pH 1.2	0.020±0.030
4.2 pH	2.018 ± 0.085
6.8 pH	8.124±0.060
7.4 pH	6.054 ± 0.015
8.0 pH	5.692 ± 0.017

* All values are expressed as mean±SD, n=3

Density:

The loose bulk density (LBD) and tapped bulk density (TBD) were determined and calculated using the following formulas.

Compressibility Index⁷

The compressibility index of the powder blend was determined by Carr’s compressibility index.

Hausner's Ratio

Hausner's ratio was determined by following formula.

Preparation of Sustained Release (SR) Matrix Tablets:

Different tablet formulations were prepared by direct compression method. According to different batches, aceclofenac, xanthan gum, guar gum, HPMC K4M, microcrystalline cellulose, PEG 6000, PVP K30, were mixed using pestle and mortar to get uniform mixture. Xanthan gum and guar gum were used as matrix-forming material, while microcrystalline cellulose was used as a diluent. This mixture was then blended with magnesium stearate (used as a lubricant). All ingredients were passed through a # 60 sieve and compressed by using 8 mm round flat-faced punch of rotary tablet machine (Karnavati, India). Compositions of all batches were represented in Table I.

Evaluation of Postcompression Parameters of Sustained Release Tablet:⁸

Tablets were evaluated for thickness, diameter, weight variation, drug content, hardness and friability, performed according to the IP ’1996.

Thickness and Diameter:

The thickness and diameter of tablets were determined using a Digimate caliper (Japan). Three tablets from each batch were used and average values were calculated.

Figure 2. DSC thermogram (A-B, C-D)

A indicate aceclofenac; B indicate aceclofenac +xanthan gum; C indicate aceclofenac +xanthan gum +guar gum; D indicate aceclofenac+ guar gum +HPMC K4M

Weight variation test:

To study weight variation, 20 tablets of each formulation were weighed using an electronic balance (Shimadzu AUX120) and the test was performed according to the official method.⁹

Drug content:

Three tablets were crushed and powder containing 100 mg of aceclofenac was dissolved in 100 ml of methanol. The solution was passed through a millipore filter Nylon 66 (pore size 0.45 mm)and analyzed spectrophotometrically (Shimadzu UV-1700) at 275nm.

Table III. Pre compression Parameter of different batches of aceclofenac*

Batch No	Angle of repose (ө)	LBD (gm/ml)	TBD (gm/ml)	Carr’s Index (%)	Hausner ratio
A	29.04	0.27	0 .298	9.39	1.103
B	28.66	0.259	0.30	13.6	1.158
C	28.01	0.271	0.3011	10	1.11
F1	28.04	0.254	0.282	9.92	1.15
F2	27.92	0.287	0.318	9.74	1.1
F3	28.08	0.269	0.294	12.6	1.12
T1	29.1	0.274	0.312	11.4	1.19
T2	28.36	0.264	0.297	10.9	1.22
T3	28.3	0.280	0.310	9.6	1.10
T4	27.6	0.275	0.298	7.71	1.08

* Each value represents as mean ± SD of 3 determinations.

Table IV. Evaluation of physical properties of tablets

Batch	*Drug Content (%)**	Weight variation* (mg)**	*Thickness (mm)**	Hardness (kg/cm²)**	Friability^#(%)
A	99±0.17	401.02(1.5)	3.55(0.11)	5.9(0.36)	0.34
B	98±0.22	399.62(2.58)	3.65(0.3)	6.21(0.48)	0.40
C	98±0.25	399.95(1.39)	3.58(0.12)	5.85(0.37)	0.38
F1	99±0.55	399.31(2.24)	3.55(0.09)	5.78(0.27)	0.55
F2	98±0.68	398.96(1.96)	3.5(0.10)	5.83(0.41)	0.41
F3	98±0.24	398.49(2.39)	3.36(0.11)	6(0.37)	0.48
T1	98±0.36	449.8(2.46)	4.40(0.14)	5.5(0.27)	0.25
T2	98±0.64	448.7(3.29)	4.52(0.09)	5.31(0.20)	0.30
T3	98±0.54	450.65(2.45)	4.57(0.03)	5.38(0.31)	0.18
T4	101±0.28	448.5(2.25)	4.49(0.04)	5.53(0.31)	0.34

All values are expressed as mean± SD; *n=3, **n=6. ***n=20, ^#n= each value represents as singly.

Table V. Kinetic values obtained from different plots of formulation

Optimized Batches	Zero order*	First order plots**	Higuchi’s plots***	Korsemeyer Peppas plots****
Optimized Batches	Regression Coefficient (R²)	Regression coefficient (R²)	Regression coefficient (R²)	Slope (n)	Regression Coefficient (R²)
C	0.9344	0.9183	0.9637	2.0996	0.9748
F3	0.9176	0.9091	09377	0.7205	0.9887
T4	0.9859	0.9316	0.9659	0.8635	0.9728

* = zero order equation, C= K_Ot, ** = First- order equation, Log C= log C₀-K_t/2.303., *** = Higuchi’s equation, Q= K_t^1/2., ****= Korsmeyer Peppas equation, M/M_α=Ktⁿ.

Hardness and Friability:

For each formulation, the hardness and friability (%) of 6 tablets were determined using Monsanto hardness tester and Roche Friabilator respectively.

In Vitro Dissolution Test:

The in vitro dissolution studies were carried out using USP Type І dissolution apparatus at 50 rpm. The dissolution medium consisted of 1.2 pH buffer (900 ml) for first 2 hrs and then replaced by phosphate buffer (pH 6.8) for 3 to 24 hours (900 ml), maintained at 37±0.5⁰C.

5ml of sample was withdrawn and replaced by an equal volume of fresh dissolution medium of same pH. The drug release at different time interval was measured by UV-visible spectrophotometer (Shimadzu UV-1700) at 275nm. The results were calculated by considering ±SD of 3 determinations.

Drug Release Kinetic Study:

To study the release kinetics, data obtained from in vitro drug release studies were plotted in various kinetic models: zero order (Equation 6) as cumulative amount of drug released vs. time, first order (Equation 7) as log cumulative percentage of drug remaining vs. time, and Higuchi’s model (Equation 8) as cumulative percentage of drug released vs. square root of time.¹⁰

Where K₀is the zero-order rate constant expressed in units of concentration/time and t is the time in hours. A graph of concentration vs. time would yield a straight line with a slope equal to K₀ and intercept the origin of the axes.

Where C₀ is the initial concentration of drug, k is the first order constant, and t is the time in hours.

Where K is the constant reflecting the design variables of the system and t is the time in hours.

Mechanism of Drug Release:

To evaluate the mechanism of drug release from sustained release tablet, data for the drug release was plotted in Korsmeyer- Peppas equation as log cumulative percentage of drug released vs. log time (Equation 9) and in Hixson-Crowell cube root equation (Equation 10) as cube root of cumulative percentage drug released vs. time. Because aceclofenac is sparingly soluble drug and in sustained release preparation of drugs with poor solubility shows dissolution after following erosion mechanism of the matrix system^11-12. The release exponent n and k value was calculated through the slope of the straight line.

Where M_t/M_∞ is the fractional solute release, t is the release time, K is a kinetic constant characteristic of the drug/polymer system, and n is an exponent that characterizes the mechanism of drug release.

Where Mo is the original mass of the drug particle, M is the mass of drug undissolved, K is kinetic constant and indicates time required.

For matrix tablets, if the exponent n < 0.5, then the drug release mechanism is quasi - Fickian diffusion, if n = 0.5 then Fickian diffusion, 0.5 < n < 1, then it is anomalous diffusion. An exponent value of 1 is indicative of Case-II Transport or typical zero-order and n > 1 non-Fickian supercase II. The diffusion exponent is based on Korsmeyer- Peppas equation and the erosion exponent is based on Hixson-Crowell cube root equation.

Stability Studies of Sustained Release Tablets:

Stability study was carried out to observe the effect of temperature and relative humidity on optimized formulation C, F3 and T4 be sealed in aluminum packing, coated inside with polyethylene and placed in stability chamber (Programmable Environmental Test Chamber, Remi, Mumbai) for 3 months. Stability study was carried out at 45^oC ±2⁰C temperature and 75% relative humidity (RH). After 1, 2, and 3 months interval, placed samples were analyzed for physical evaluation include physical appearance, drug content and drug release characteristics.¹³

RESULTS:

Solubility Studies of Aceclofenac:

The results of solubility study of aceclofenac in various pH media were represented in Table II.

Drug–Excipients Interaction Study:

Thin Layer Chromatography:

The results of TLC study indicate no change in the R_fvalue of drugs and no interaction between drug and excipient was found.

FTIR Spectra:

The FTIR spectra of pure aceclofenac and its physical mixtures with other excipients are shown in Figure1 (A, B, C and D). Pure aceclofenac showed 1772.6, 1647.2, 1508.3, 1452.4, 1419.6, 1344.4, 1255.7, 1149.6, 1055.1, 898.8, 750.3 cm^-1 wave number as major peaks. The results revealed no considerable changes in the IR peak of aceclofenac when mixed with polymers compared to pure aceclofenac.

DSC Spectra:

The DSC thermogram of pure aceclofenac and its physical mixtures with other excipients are shown in Figure2 (A, B, C and D). DSC study demonstrates that no change in the individual peaks of aceclofenac thermograms.

Evaluation of Precompression Parameters of Sustained Release Tablets:

Angle of Repose, Bulk Density, Compressibility Index and Hausner’s Ratio:

Prior to the compression the blend of all batches of aceclofenac were evaluated for various pre compression parameters such as angle of repose, bulk density i.e. (loose bulk density, tapped bulk density), compressibility index and Hausner’s ratio. Results showed that all parameters are in limits. Hausner’s ratio < 1.25 for both optimized batches indicates good flow properties. The results of all the batches of aceclofenac are represented in Table III.

Evaluation of Postcompression Parameters of Sustained Release Tablets:

Weight variation, Drug content, Thickness, Hardness, Friability:

Tablet properties such as weight variation, thickness, hardness, friability and drug content of all batches were evaluated. All batches pass weight variation (between 90%-110%). Drug content of all batches was found within limit (90%-110%). Thickness of tablet was found variation less than 5%. Hardness and friability of all batches were found 6.1±0.024 to 7.4±0.030 and <1% respectively. The results of physicochemical evaluation of tablets are given in Table IV.

In Vitro Dissolution Test:

The results obtained from the dissolution studies of various batches A, B, C, F1, F2, F3, T1, T2, T3 and T4. Among these batches, the batch C containing xanthan gum ( 1:0.12), F3 containing mixture of xanthan gum and guar gum ( 1:0.06:0.02) and T4 containing guar gum and HPMC K4M (1:0.05:0.15 ) showed 98.64, 99.13 and 95.35 cumulative percent drug release at the end of 24 hours respectively. The graphical representations of dissolution study of all batches were shown in Figure 3.

Figure 3. In vitro release of aceclofenac from A, B, C, F1, F2, F3, T1, T2, T3.T4. *Each point represents mean ± SE; n=3.

Drug Release Kinetic and Mechanism Study:

The release exponent (n) was calculated from the slope of the appropriate plots, and the regression coefficient (R²) was determined. In vitro dissolution kinetic study of batch C by Korsemeyer- Peppas equation shows regression coefficient, R² = 0.9748 with release exponent, n = 2.0996, that means it follows super case-II transport mechanism, that indicates the polymer relaxation mechanism. Similarly, the formulation F3 and T4 showed good linearity (R² = 0.9887, 0.9728) with slope (n = 0.7205, 08635) respectively that appears to indicate that the drug release mechanism is anomalous transport, which reveals that both drug diffusion and polymer relaxation mechanism. It might be due to the poor aqueous solubility of the aceclofenac or effect of diluent concentration. The Hixson-Crowell equation for C, F3 and T4 showed R²=0.9559, 0.9503, 0.9024 respectively which also supports polymer relaxation mechanism. The release rate kinetic data for all batches can be shown in Table V.

Stability Studies:

The result of stability studies indicated that, the tablets did not show any physical changes (hardness, friability, color) during the study period and the drug content of optimized batches C, F3, and T4 (n=3; 100 % ± 1.089) was found within pharmacopoeal limits. The in-vitro dissolution study of all optimized batches (C, F3 and T4) showed 97.98, 98.56 and 94.35 % drug release respectively at the end of 3 months. This indicates that all these optimized batches are stable for short term storage condition. However real time of stability studies for a period of 2 year are required to establish the stability of developed product.

DISCUSSION:

The present research work reflects an attempt to formulate once daily directly compressed sustained release tablet of aceclofenac by using hydrophilic polymers like xanthan gum, guar gum and HPMC K4M in alone and combination. This study was aimed to employ direct compression method for which the drug and polymer should have to be possessing good flow properties. Aceclofenac has extremely poor flow property which was also found to be changed in the presence of polymers so that flow property improving directly compressible vehicle like microcrystalline cellulose (MCC) pH 102 was employed.

The solubility study showed that less than 0.1 percent solubility of aceclofenac both in water and 1.2 pH. The aceclofenac showed pH dependent solubility. As the pH of the medium changes from acidic to basic (i.e. 1.2 to 6.8pH), the solubility was drastically improved. The results of TLC, FTIR and DSC study showed that there were no drug-excipient interactions. All the optimized batches were in accordance to pharmacopoeial limits for pre and post compression parameters.

The in-vitro drug releases of all batches were studied in simulated gastric (1.2) and intestinal fluids (6.8) for a period of 24 hours using USP type I dissolution apparatus. The results of dissolution studies indicates that batch A, B and C released 0.64, 1 and 0.3% of aceclofenac at the end of 2 hours and 42.29, 78.93 and 98.64% respectively at the end of 24 hrs, which indicates the release rates of A, B and C formulation was found to be depend on the concentration of xanthan gum. Increasing concentration of gum in formulation results in to slower drug release rate, because of formation of thick gel of high concentration of gum that delays drug release from tablet matrix. Further as the amount of xanthan gum decreased, drug release rate was found to be increased. In B and C batches PEG6000 was incorporated as drug release modifier, to improve the dissolution rate and bioavailability and was found to be 78.93 % and 98.64 % respectively. In the F1, F2 and F3 batches, the results of dissolution studies indicated that F1, F2 and F3 released 0.54%, 0.86%, 0.53%, in 1.2 pH for 2 hrs and 59.16%, 84.24%, 99.13% in 6.8 pH at the end of 24 hrs. Xanthan gum and guar gum were used in synergistic combination for sustaining the drug release to form a swellable sustained release matrix and also as a binding agent while PEG-6000 forms the erodible matrix along with the solubility enhancing property for poorly water soluble drugs like aceclofenac. Further in T1, T2, T3 and T4 batches guar gum and HPMC were used because guar gum alone can not efficient for controlled drug release. The combination of Guar gum and HPMC lead to a greater retarding effect. PEG6000 was also used for increasing the drug release rate because it is drug release modifier. The drug release of these batches were found to be 0.72%, 0.85%, 0.92%, 0.35% in 1.2pH for 2 hrs and 64.57%, 71.74%, 84.44%, 95.35% in 6.8pH at the end of 24 hrs.

From above results it was found that xanthan gum and HPMC has good drug release retarding property. But guar gum alone can not have a good drug release retarding property. From kinetic study it was found that xanthan gum containing batch shows complete polymer relaxation mechanism, while remaining xanthan:guargum and guar gum:HPMC were shows both diffusion and polymer relaxation mechanism. Hence the collaborative use of PEG-6000 with the natural polymers seems to be a beneficial and economic option for efficient SR formulation development.

The stability study results also found to be supports to the above results which indicates that the all optimized batches were stable in there appropriate stability conditions.

CONCLUSION:

It can be concluded that the batches C, F3 and T4 releases the entire quantity of the drug at the end of 24 hour and can be used for the formulation of once daily sustained release matrix tablet of aceclofenac. This prolonged release of drug might be beneficial and effective for reliving pains of rheumatoid arthritis and anlkylosing spondylitis.

ACKNOWLEDGEMENT:

Authors are thankful to Alembic Pharmaceutical Ltd (Baroda, India) for the gift samples of aceclofenac. Author also acknowledge to Alkem (Navi Mumbai, India) for providing gift samples of xanthan gum and guar gum. Authors are grateful to Dr. S.G. Gattani for his co-operation and Principal, R.C.Patel College of Pharmacy, Shirpur for providing necessary facilities.

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Received on 23.08.2009 Modified on 20.11.2009

Research J. Pharm. and Tech. 3(1): Jan. - Mar. 2010; Page 168-174