FORMULATION, DEVELOPMENT AND IN VITRO EVALUATION OF TRAMADOL EXTENDED-RELEASE TABLETS

Objective : The objective of the present study was to develop “once daily” extended-release tablets of tramadol (100 mg) by wet granulation using hydrophilic polymer like hydroxypropyl methylcellulose K100M, K15M and polyethylene oxide (PEO). Methods: The tramadol matrix tablets were prepared by using different polymers like hydroxypropyl methyl cellulose (HPMC K15M and K100M), polyethylene oxide (PEO) as the nontoxic and easily available suitable matrix system. The extended-release tablets of tramadol (400 mg) were prepared wet granulation technique. Different pre-compression and post-compression were performed. In vitro dissolution tests were performed and percentage drug release was calculated. The Fourier-transform infrared spectroscopy (FTIR) studies conducted on pure drug tramadol and the optimized formulation (T6). Different release models like zero order, first order, higuchi and Korsemeyer-Peppas were applied to in vitro drug release data in order to evaluate the drug release mechanisms and kinetics. Results: Pre-compression and post-compression parameters satisfied with pharmacopeia specifications. The In vitro release studies were performed using USP type II apparatus showed that optimized formulation T6 consisting of polyethylene oxide (PEO) with 25 mg of the polymer was found to extended release of tramadol over a period of 24h. The optimized formulation T6 followed the zero-order kinetics as correlation coefficient (r 2 Conclusion: The present study shows that polyethylene oxide was found to play a great role in controlling release of tramadol from the matrix system. Accordingly, it can be concluded that the formulation is robust in the performance is less likely to be affected by the various factors studied. ) values are higher than that of first-order release kinetics. In order to understand the complex mechanism of drug release from the optimized formulation T6 matrix system, the in vitro release rate were fitted to Korsemeyer-Peppas model and the release exponent value (n) obtained was 0.82105 exhibited anomalous (non fickian) diffusion mechanism.


INTRODUCTION
Oral drug delivery is the largest and the oldest segment of the total drug delivery market. It is the fastest growing and most preferred route for drug administration. Increased complications and expense involved in the marketing of new drug entities have focused greater attention on the development of sustained release (SR) or controlled release (CR) or extended release (ER) drug delivery systems [1][2][3]. Sustained release (SR) or controlled release (CR) or extended release (ER) delivery systems can achieve predictable and reproducible release rates, extended duration of activity for short half-life drugs, decreased toxicity, and reduction of required dose, optimized therapy and better patient compliance. Sustained release (SR) or controlled release (CR) or extended release (ER) drug delivery systems are designed by different techniques like enteric coating, osmotic pump, prodrugs, transdermal patches and matrix tablets. Among the various techniques used, recently the attention of pharmaceutical researchers has been attracted by the matrix tablets. Matrix type sustained delivery systems are popular because of their ease of manufactures. It excludes complex production procedure such as coating and pelletization during manufacturing and drug release from the dosage form. It is controlled mainly by the type and proportion of the polymers used in the preparation. Hydrophilic polymer matrix system are widely used for designing oral sustained release delivery systems because of their flexibility to provide a desirable drug release profile, cost-effectiveness, and broad regulatory acceptance [4,5].
Tramadol HCl (TmH) is a centrally acting opioid and nonopioid analgesic. TmH acts as an opiate agonist, through selective binding to the μ-opioid receptor, and weak inhibition of norepinephrine and serotonin uptake. It is used when non-steroidal anti-inflammatory drugs (NSAIDs) fail to mitigate pain. It works in the brain to change how your body feels and responds to pain. It's also used to treat long-standing pain when weaker painkillers not work.
The aim of the study was to develop "once daily" extended-release tablets of tramadol (100 mg) for the treatment of severe acute and chronic pain. Tramadol is readily absorbed after oral administration because of tramadol belongs to BCS class I drug has a good bioavailability 68-72 % and short half-life (t1/2

MATERIALS AND METHODS
= 5-6 h). It is prescribed 3-4 times a day usual dosage regimen of 50-100 mg and a maximum dose 400 mg (50 mg 4 times a day). This frequent dosing schedule cause an increased incident of side effects, noncompliances and development of tolerance especially in long term used like osteoarthritis, arthritis, post-surgical pains etc. [6,7]. It can be suggested that there is a strong clinical implication of SR formulation of this drug.

Materials
Materials used in this study were obtained from different sources. Tramadol a gift sample from Chandra lab, hyderabad. Hydroxypropyl methylcellulose (HPMC K15M and K100M), polyethylene oxide (PEO), magnesium stearate procured from ISP, Hyderabad. Microcrystalline cellulose procured from loba chemie pvt ltd, Mumbai. Talc procured from SD fine chemicals pvt ltd, Mumbai. objective of pre-formulation studies is to generate information useful to the formulator in developing stable dosage forms [8].

Colour, odour and appearance
The drug sample was evaluated for its colour and odour. The results are shown in table 8.

Determination of solubility
The solubility of drug tramadol is determined by using a different solvent like water, methanol and acetone. The result are shown in table 9.

Determination of λmax
Standard stock solution: 100 mg of tramadol was dissolved in a sufficient amount of methanol and makeup to 100 ml with 0.1N HCL to give a concentration of 1000 μg/ml (stock solution A).
Scanning: From the stock solution (stock A) pippet out 1 ml and was make up to 10 ml to give a concentration 100μg/ml (stock solution B) was prepared and UV scan was taken between 200 to 400 nm. The absorption maximum was found to be 270 nm and was used for further analytical studies [9,10].

Calibration curve of tramadol in 0.1 N HCL
From this stock solution dilutions were made in 0.1 N HCL in order to get 2μg/ml, 4 μg/ml, 6 μg/ml, 8μg/ml, 10μg/ml, the absorbance of these solutions were measured at λ max Standard Stock solution: 100 mg of tramadol was dissolved in a sufficient amount of ethanol and makeup to 100 ml of pH6.8 phosphate buffer to give a concentration of 1000 μg/ml (stock solution A). From the stock solution (stock A) pippet out 1 ml and was make up to 10 ml to give a concentration 100μg/ml (stock solution B), from this stock solution subsequent dilutions were made in phosphate buffer pH 6.8 in order to get 2μg/ml, 4μg/ml, 6μg/ml, 8μg/ml, 10μg/ml, absorbance of these solutions were measured at λmax 270 nm using uv-visible spectrophotometer and standard curve was plotted. The linearity plot was obtained for the aliquot concentration of 2, 4, 6, 8; 10μg/ml with the absorbance was seen at 270 nm [11][12][13][14].
270 nm using UV-visible spectrophotometer and the standard curve was plotted. The linearity plot was obtained for the aliquot concentration of 2, 4, 6, 8; 10μg/ml with the absorbance was seen at 270 nm.

Drug-excipient compatibility study
Infrared spectroscopy is a useful analytical technique utilized to check the chemical interaction between the drug and excipients used in the formulation.1-2 mg of solid fine powder of drug tramadol and 200-300 mg of dry powder of KBr (IR grade) were taken in a mortar and mixed well with the help of a spatula. Spectrum measurement was carried out using KBr disk method in the wavelength region of 4000-400 cm-1 by FTIR spectrophotometer [15][16]. The IR spectrum of the physical mixture was compared with that of the pure drug to check any possible drug-excipient interaction. The spectrum of FT-IR is shown in fig. 4 and 5.

Formulation of an extended-release tablet
In the formulations prepared, the release retardants included were hydroxyl propyl methyl cellulose (HPMC K15M, HPMC K100M CR), polyethylene oxide (PEO) and microcrystalline cellulose (MCC), magnesium stearate (MS) 1% and talc 2 % were used as lubricants. 5% w/v solution of polyvinyl pyrrolidone (PVP-K30) in isopropyl alcohol (IPA) was used as a binder. Compositions of different formulations were given in the following tables no 1-3. Microcrystalline cellulose, PVP K30 were weighed according to the given table and sifted through 40 mesh. To the above blend tramadol was added and sifted through 18 mesh. The sifted materials were mixed for 10 min. Magnesium stearate and talc were weighed and sifted through 40 mesh. To the powdered blend, the lubricated blend was added and mixed properly. Then the total blend was used for Pre-compression parameters and then compressed using 8 mm round punches [17][18][19][20].

Pre-compression parameters
The following pre-compression parameter was evaluated like bulk density and tapped density, angle of repose, Hausner's ratio and compressibility index (%).

Bulk density and tapped density
Both loose bulk density (LBD) and tapped bulk density (TBD) were determined. First 25 gm of the blend from each formulation was weight accurately and kept into a cleaned dried 50 ml graduated measuring cylinder. After than initial volume was noted is called as bulk volume and the bulk density is calculated by the following formula [21][22]. The results are given in the table 13.
Bulk density = Weight of blend (gram)/Bulk volume of the blend After measuring bulk volume the same measuring cylinder subject to 500 tap with the help of bulk density measuring Apparatus. The tapped volume occupied by the powder is recorded. Then the tapped density is measured by the following formula. The outcomes are given in the table 13.

Angle of repose
The angle of repose of powdered blend was determined by the funnel method. The accurately weight 15 gm powdered blend was taken in the funnel. The height of the funnel was adjusted in such a way that the tip of the funnel just touched the apex of the blend. The powdered blend was allowed to flow through the funnel freely on to the surface. The diameter of the powder cone was measured and the angle of repose was calculated using the following equation [23,24].

Hausner's ratio
Hausner's ratio is an indirect index of ease of powder flow which is calculated by the following formula. The outcomes are given in the  table 12 Hausner's Ratio =

Compressibility index (%)
It is also one of the simple methods to evaluate flow property of powder by comparing the bulk density and tapped density is calculated by the following formula [25][26][27]. The outcomes are given in the table 12

Evaluations of the tablet Thickness
The thickness of the tablets is measured by vernier calipers and it is expressed in mm. Tablet thickness should be controlled within a±5% variation of standard value the outcomes are given in table 13.

Hardness
Tablets require strength or hardness to withstand mechanical shocks of handling in the manufacture, packing and shipping. Tablet hardness was measured by monsanto hardness tester and results are expressed in Kg/cm 2

Weight variation test
. The outcome are given in the  table 13 20 tablets were weighed individually. Average weight was calculated from the total weight of all tablets. The individual weights were compared with the average weight. The percentage difference in the weight variation should be within the permissible limits (±5%). The percent deviation was calculated using the following formula. The acceptance limits are as per United States pharmacopeia (USP) [28]. The outcome are given in the table 13

Friability
It was performed in roche friabilator where the tablets were subjected to the combined effect of abrasion and shock by utilizing a plastic chamber that revolves at 25 rpm dropping the tablets at a distance of six inches with each revolution in the chamber. Preweighted samples of 20 tablets were placed in the friabilator, which is then operated for 100 revolutions. The tablets are then dusted and reweighed. Permitted friability limit is 1.0%. The percent friability was determined using the following formula [29][30].

Drug content uniformity
The content uniformity test is used to ensure that every tablet contains the amount of drug substance intended with little variation among tablets within a batch. Randomly 30 tablets were selected from which 10 tablets were taken and triturated well in a mortar. The quantity equivalent to 100 mg of tramadol was dissolved in 100 ml of phosphate buffer pH 6.8 solutions on a rotary shaker overnight. The absorbance was measured using UV-Visible spectrophotometer at 270 nm [31][32]. The outcomes are given in the table 13.

In vitro dissolution studies
The dissolution rate of extended-release tablets from all formulations was performed using LAB INDIA dissolution apparatus (USP II) with paddle. The dissolution fluid was 900 ml 0.1N HCL for first 2 h then replaced with phosphate buffer pH 6.8 at a speed of 50 rpm and a temperature of 37±0.5 °C were used in each test. The dissolution experiments were conducted in triplicate. For all tests 5 ml samples of the test medium were collected at set intervals (1, 2, 4, 6, 8, 12, 18and 24 h) and were replaced with equal volume of phosphate buffer pH 6.8. The samples were analyzed at 270 nm using a UV spectrophotometer [33][34][35].

Kinetic analysis of dissolution data
In order to determine the release mechanism that provides the best description to the pattern of drug release, the in vitro release data were fitted to zero-order, first-order, hixson crowell, and Korsemeyer-Peppas model [36][37]. The data of the regression coefficient of different kinetic models were summarized in table 17.

RESULTS
Preformulation study: These test results were illustrated below

Standard graph of tramadol in 0.1 N HCl
In the pre-formulation study, it was found that the λmax of tramadol by the spectrophotometric method in phosphate buffer 0.1N HCL was found to be 270 nm. The spectrum was shown in fig.

Drug and excipients compatibility studies
FTIR studies conducted on pure drug tramadol and the optimize formulation (T6) given in fig. 4 and 5, which showed that there is no marked interaction between drug and excipients used.

Characterization of tramadol powder blend
The blends for tramadol tablets were characterized with respect to the angle of repose, bulk density, tapped density, carr's index, and hausner's ratio. Angle of repose was between 22.7 ° to 28.5 ° and carr's index values were less than 15 for the blend of all the batches indicating excellent to good flowability and compressibility. Hausner's ratio was less than 1.25 for all the batches indicating excellent flow properties. The results were summarized in table 12.

Evaluation of physical parameter
The physical properties of tramadol extended-release tablets were given in table 13. Tablet thickness should be controlled within a±5% variation of standard value. The prepared tablets in all the formulations possessed good mechanical strength with sufficient hardness in the range of 6.0±0.21 to 6.7±0.41 kg/cm 2 . Friability values below 1% (0.32±0.62-0.42±0.42%) were an indication of good mechanical resistance of the tablets. All the tablets from each formulation passed weight variation test, as the % weight variation was within the pharmacopoeial limits of±5% of the weight. The weight variation in all the formulations was found to be 398±1.56 to 409±1.23 mg, which was in pharmacopoeial limits of±5% of the average weight. The percentage drug content of all the tablets was found to be between 98.2±0.66% to 103±0.68% of Tramadol which was within the acceptable limits.       --------*Average of three observations (n=3), *All the values are expressed as mean±SD

Kinetic studies for optimized formulation
For analyzing the release mechanism, the data obtained were fitted to various kinetic equations of Zero order, First order, Higuchi model and Korsmeyer-Peppas model. The regression coefficient was calculated. It was concluded that the optimized formulations T6 follows zero order kinetics as correlation coefficient (r 2 ) values are higher than that of first-order release kinetics. In order to understand the complex mechanism of drug release from the matrix system, the in vitro release rate were fitted to korsmeyer-peppas model and interpretation of release exponent value (n) enlighten in understanding the release mechanism from the dosage form. The release exponent value (n) obtained was 0.82105. The T6 formulation exhibited anomalous (nonfickian) diffusion mechanism. Kinetic studies shows that the amount of drug from the matrix system was by both diffusion and erosion. There is a good scope for the development of extended-release tablets for this drug. The data of the regression coefficient of different kinetic models were summarized in table 17.

CONCLUSION
An extended release tablet of tramadol was prepared by wet granulation using polymer like hydroxypropyl methylcellulose K100M, K15M and polyethylene oxide (PEO). Based on the stated results of formulation coded T6 shows more sustained action and optimum release than remaining all, which indicates that the concentration of polymer polyethylene oxide was found to play a vital role in controlling the release of tramadol from the matrix system. Accordingly, it can be concluded that the formulation is robust in the performance is less likely to be affected by the various factors studied.

AUTHORS CONTRIBUTION
All the author have contributed equally

CONFLICTS OF INTERESTS
The author of this study declared no conflict of interest