Development and Characterization of The Celecoxib Matrix Tablet

Two of the most prevalent, as well as disabling musculoskeletal disorders, are osteoarthritis and rheumatoid arthritis in millions of individuals across the globe and, particularly, among elderly individuals. These inflammatory conditions are linked to the progressive loss of joints, cartilage, chronic pains, stiffness and loss of functions that impact the quality of life and routine of the patients. [1]. These disorders are primarily treated pharmacologically by using nonsteroidal anti-inflammatory drugs (NSAIDs) which shows symptomatic relief by inhibiting the production of cyclooxygenase (COX) enzymes that synthesize prostaglandins [2].The roles of prostaglandins are very important in mediating pain, inflammation and fever reactions, and COX inhibition is an effective treatment for arthritis. But traditional nonselective NSAIDs inhibit both isoenzymes COX-1 and COX-2 resulting in a spectrum of adverse effects with GI complications such as ulceration, bleeding and perforation being the greatest. The identification and description of the COX-2 isoenzyme as the one that is mostly inducible during inflammatory events and COX-1 is constitutively expressed in different tissues transformed the development of anti-inflammatory drugs and gave rise to selective COX-2 inhibitors that had similar levels of effectiveness and better gastrointestinal safety profiles.[4]. The most widespread inhibitor of selective COX-2 with a molecular weight of 381.38 Da  is chemically referred to as 4-[5-(4-methylphenyl)-3- (trifluoromethyl)-1H-pyrazol-1-yl] benzene sulphonamide, and belongs to the diaryl-substituted of the pyrazole class. This sulphonamide-containing molecule has a selectivity ratio 10 to 100 fold greater than that of the nonselective NSAIDs, and this interaction is what confounds this molecule as the selectivity o approach taken by the enzyme of COX-2, rather than the approach taken by the enzyme of COX-1 [4]. Celecoxib has been provided with a regulatory support by the United States Food and Drug Administration to be used in the management of osteoarthritis, rheumatoid arthritis, acute pain, primary dysmenorrhea, ankylosing spondylitis, and familial adenomatous polyposis with proposed dosage of 100 to 200mg once or twice daily. However, just like any other drug, the administration of celecoxib is not free of side effects and side effects such as complicated ulcers and general gastrointestinal discomforts such as dyspepsia, abdominal pain and nausea occur less frequently than with the traditional NSAIDs like naproxen, ibuprofen and diclofenac as demonstrated in the CLASS (Celecoxib Long-term Arthritis Safety Study) trial which is among the largest clinical trials of celecoxib. [5]. However, even with the enhanced safety profile, Celecoxib has a biopharmaceutical perspective whose formulation is of great concern since it is a Biopharmaceutics Classification System (BCS) Class II drug with a high intestinal permeability but very low aqueous solubility and was reported to dissolve 3-7 1g/mL in water [7]. It is a pH-soluble crystalline lipophilic molecule, virtually insoluble in acidic gastric acid and slightly soluble in intestinal fluids, which grossly inhibits its rate of dissolution and in turn its oral bioavailability.

After oral administration of standard dosage forms, celecoxib exhibits inconsistent and partial absorption with an absolute bioavailability of between 22-40 % in formulation of capsules and between 64-88 % in formulation of solution as the rate-limiting step to absorption [5]. When in solution the drug is absorbed quickly through the gastro intestinal tract, with peak plasma concentrations (C_max) being achieved in about 2-3 hours, followed by an extensive hepatic metabolism mainly by the cytochrome P450 2C9 (CYP2C9) to inactive metabolites, giving an elimination half-life of about 7-11 hours. The limited elimination half-life indicates the need to have several dosing schedules daily with traditional preparations to sustain the required drug levels in the body that can result in periodic spikes through drug levels in the body, which  adversely affects and decreased patient adherence [5].

Furthermore, it has been shown that food has a large impact on the absorption of celecoxib in solid dosage forms and this is characterized by high-fat meals which increase the systemic exposure by 3 to 5 fold because of improved dissolution in lipid-rich environments, although it is less effective in humans than in the animal models. It is  insoluble and this means that it has dose-related pharmacokinetics and significant inter-individual difference in drug exposure thus complicating therapeutic outcomes further. [6]. Numerous strategies have been investigated to enhance the solubility and dissolution of celecoxib that includes reduction of particle sizes through micronization and nano-milling, solid dispersion through hydrophilic carrier like polyvinylpyrrolidone (PVP) and polyethylene glycol, inclusion complexation with cyclodextrin, self-emulsifying system of delivering drugs, entrapment in solid lipid nanoparticles and nanostructured lipid carrier. Although such methods have shown to enhance the solubility of celecoxib 4 to 132 fold and increase the rate of dissolution, they can be complex to manufacture, require specialized equipment, experience stability issues, and do not allow a patient to achieve steady therapeutic drug levels over time, all in addition to achieving a single daily dose, as well as allowing the drug to be administered once a day, unlike twice or thrice a day [7]. Controlled-release dosage forms of celecoxib provide an alternative solution which can simultaneously help to achieve multiple therapeutic goals Hydrophilic matrix tablet systems are some of the controlled-release technologies that have become very appealing because they are quite easy to formulate and make, are cost-effective, can easily accommodate drugs of different physicochemical characteristics, are highly reproducible, and have already been accepted by regulators as such [9].

Matrix tablets are oral solid dosage types, where the active pharmaceutical ingredient is both uniformly dispersed or dissolved within a polymeric carrier, and this carrier is in charge of drug release as either diffusion, erosion or a combination of the two release processes. Hydrophilic polymer matrices operate by quick uptake and swelling of water when in contact with the aqueous media to create a viscous gel layer at the top of the tablet acting as a barrier to additional water uptake into the tablet core and diffusion of drug outwards of the tablet into the dissolution medium [10]. The gel layer thickness increases as the water continues to penetrate into the tablet at the same time the outer hydrated gel layer is dissolved and eroded through the disentangling of polymer chains, which eventually forms a dynamic equilibrium between the gel formation and erosion processes [11]. Such matrices release the drug using diffusion as the main method of drug release in water-soluble drugs and through the process of matrix erosion and polymer relaxation in poorly soluble drugs such as celecoxib. Hydroxypropyl methylcellulose (HPMC) is a semi-synthetic derivative of cellulose, produced by chemical modification of natural cellulose, which can be considered as the best studied and widely used hydrophilic polymer in the production of tablet formulations because of its superior gel-forming qualities and concentration-dependent viscosity, pH-independent swelling characteristics across the physiological pH range (2-13), lack of enzymatic degradation in the gastrointestinal tract, regulatory acceptance, and cost-effectiveness. [1 It can also be further modulated by incorporation of more polymers like ethylcellulose (hydrophobic polymer) that decreases the rate of drug release, carboxymethyl cellulose sodium (an anionic hydrophilic polymer), carbopol (polyacrylic acid synthetic polymer), and several other cellulosic derivatives, in addition to the ratio of polymer to the drug, porosity of the tablet, and compression force [13].

Various researchers have reported the development of celecoxib matrix tablets based on various polymeric blends so as to have a longer duration of drug release of between 8 and 24 hours. It has been shown that celecoxib is capable of being released at the 12-18 hrs depending on the concentration and polymer combination used, with dissolution profiles characterized as either being zero-order, first-order, or Higuchi depending on the polymer combination specific to that compound. Combinations of HPMC and ethylcellulose were found to have better retardation and increased linearity in release profiles, whilst carboxymethyl cellulose with HPMC formulations were found to have concentration-independent zero-order release kinetics with correlation coefficients above 0.98.[14]. The targeted release of celecoxib using natural polysaccharide guar gum, pectin, amylose, and resistant starch as matrix tablets have demonstrated good specifications in the targeted delivery of drugs followed by minimal release (<10) in simulated gastric and intestinal environment and maximum release (>90) in simulated colonic environment after 24 hours. [15] The matrices are particularly useful in the treatment of inflammatory bowel disease and colorectal diseases where local drug delivery is required. Pharmacokinetic analysis of celecoxib nanostructured lipid carriers in comparison to the conventional Celebrex capsules has shown that advanced formulations have the potential to increase area under the plasma concentration-time curve (AUC) up to 1.54-folds and extend the elimination half-life of the drug, as well as decrease the cardiovascular risks of regularly taking high doses of celecoxib. [11] Although these advances have been made, a thorough evaluation of celecoxib matrix tablet formulations should be conducted through systematic investigation.

MATERIALS AND METHOD

MATERIALS:

All the chemicals including Celecoxib were of analytical grade and obtained from standard suppliers. Celecoxib gift sample was received from Sangeeta Pharmaceuticals, Sinnar, Maharashtra and Pullulan, Xanthan gum, Chitosan, Polyvinylpyrrolidone K30(PVP K30), Magnesium stearate, Talc and Microcrystalline cellulose (MCC) were purchased from Research Lab Fine Chem, Mumbai. All chemicals and excipients were used as received without any further purification and double distilled water was also employed throughout all the investigation.

METHODOLOGY:

Determination of λmax

A stock solution (100 µg/mL) of Celecoxib was prepared in ethanol, sonicated and filtered. An aliquot of this solution was diluted and the absorbance of the sample was determined (200-400 nm) in a UV spectrophotometer to estimate the maximum wavelength of maximum absorption.

Calibration Curve

A stock solution of 100 mg/mL was prepared in ethanol, and dilutions up to 5, 10, 15, 20 and then 25 mg/ml for the preparation of calibration curve. Absorbance of each concentration was recorded at 255 nm against blank and calibration graph (absorbance versus concentration) was made to ensure that the graph linearity falls in the range of analysis.

Fourier Transform Infrared (FTIR) Study.

The FTIR measurements were carried out using the Attenuated Total Reflectance (ATR) method. A small quantity of sample was directly mounted and squashed with the ATR crystal. The spectra were taken within the 4000-400 cm -1 range.

Drug-Excipient Compatibility Study.

Compatibility between the drug and excipients was analysed using FTIR for physical mixtures of Celecoxib with the excipients (1:1). They were compared with the spectrum of pure drug to determine any chemical reaction or change in characteristic peaks, no incompatibility was observed.

Celecoxib Sustained-Release Tablets Formulation.

Matrix tablets of celecoxib were prepared by direct compression method employing different proportions of Pullulan, Xanthan gum and Chitosan as matrix forming polymers mentioned in Table 01. All batches contained Celecoxib, PVP K30 as binder, magnesium stearate as lubricant,, of talc as glidant, and of microcrystalline cellulose as filler to maintain the total tablet weight of 400 mg. All materials were accurately weighed, sifted through a 60-mesh sieve and mixed homogeneously and compressed into tablets by rotary compression machine.

Table 01: Formulation Table

The free and compacted flowability as well as the compressibility of powder mixtures was examined before compression. The interparticle frictional forces measuring fixed funnel method was conducted to find the angle of repose. Bulk and tapped densities were performed dissolving the pre-weighed sample in a graduated cylinder, and the measurements delivered values that allowed calculation of Carr's compressibility index and Hausner ratio. Lower compressibility indices and Hausner ratios indicated the flow was good; and thus the direct compression can be done.

Assessment of Post-Compression Parameters.

Weight Variation:

The weight variation was determined by weighing twenty tablets from each batch on an individual basis employing the digital balance. Average and standard deviation was calculated. Results were compared with pharmacopeial limits to ensure uniformity of tablet weight indicating a constant filling action and flowability of the powder during compression.

Thickness:

The thickness and diameter of the tablets were determined by digital vernier callipers. Five tablets were taken from each batch and the mean of conditions was calculated. Homogeneous thickness and diameter for all lots ensure the uniform compression and tablet dimensional stability.

Hardness:

The tablet hardness was tested by a Monsanto Hardness Tester to evaluate the physical resistance of matrix tablets generated. Three tablets of each batch were randomly selected; and the crushing strength was measured in kg/cm². The hardness values were such that tablets had enough strength to resist handling and breaking during transportation.

Friability test:

The friability of tablets was determined with Roche Friabilator. A portion of pre-weighed tablets (20 tablets) was tumbled at 25 rpm for 4 min. They were then dedusted and weighed again after which the percentage weight loss was worked out. A friability value less than 1% was regarded as acceptable, which demonstrates good mechanical strength of the matrix tablets.

Disintegration Study

Disintegration time found by USP disintegration apparatus at 37 ± 2 ºC temperature with distilled water. The disintegration time was counted for six tablets of each batch.

Swelling Index

The swelling index of the tablets was determined by exposing the individual tablets to phosphate buffer solution (pH 7.4) at a temperature 37 ± 0.5 ºC, periodically removing them, wiping off their surface moisture with filter paper and determining weight of the tablet. The swelling index (SI) was estimated as percentage weight gain with respect to initial tablet’s weight.

Drug Content uniformity:

Drug content Ten tablets from each batch were powdered finely and an accurately weighed portion equivalent to 200 mg of Celecoxib was dissolved in methanol for drug content determination. Filtrate was filtered, diluted and the absorbance at 255 nm was determined spectrophotometrically. The content of drug was estimated compared with standard calibration curve of Celecoxib, and found to be 95-105% for each formulation.

In Vitro Dissolution

The dissolution of controlled release celecoxib tablets was determined using USP Dissolution Test, II (paddle method) at a constant temperature of 100 rpm. The dissolution medium was 1 N HCl at 37 ºC. The sample was withdrawn at a definite time interval (1, 2, 3 till 8 hours) and filtered through Whatman membrane filter and the clear solution analysed spectrophotometrically at 255 nm. The cumulative percentage of drug released was estimated by the calibration curve and sink conditions were ensured by substituting withdraw volume with fresh medium.

Drug Release Kinetics

The in vitro dissolution experiments presented the values of release that were plotted onto the various mathematical equations: zero-order, first-order, Higuchi and Korsmeyer-Peppas equations, to determine the mechanism of drug release. The correlation coefficient (R²) of each of the models was calculated and the model with the highest value of R 2 was presumed to be the most appropriate model to explain the release kinetics. This test was useful in the mechanism of action in the slow release of Celecoxib by the polymeric matrix system.

RESULT:

Determination of λmax:

The absorption spectrum was determined using an Jasco V 730 and was found to be 255 nm, depicted in fig 01. The calibration curve was plotted using regression analysis tool with R² value of 0.9912, depicted in Fig 02.

Fig 01: Absorption Spectra of Celecoxib

Fig 02: Calibration Curve

FTIR Analysis.

FT-IR was used to analyse Celecoxib with the FT-IR Alpha II Sample Compartment (Bruker), fig 03. The graph obtained was plotted with wavelength on X-axis and transmittance (%) on Y-axis. The comparison of different functional groups with the reference to parameters allowed identifying peaks at different wavelengths. These identified peaks are shown in the graph of CCB with their corresponding wavelengths.

Fig 03: FTIR study of Celecoxib

FT-IR drug-excipients compatibility study,

It was established that Celecoxib was compatible since there was no interaction between the drug and the excipient. This compatibility was proved by the graphs that show FT-IR spectra fig 04.

Fig 04: FTIR compatibility study of Celecoxib with excipients

Pre-Compression Parameters:

Pre-compression studies of all the Celecoxib matrix tablet formulations (F1–F9) depicted good flow and compressibility of blends for direct compression Table 02. The abase of repose values varied from 28.4° ± 0.6 to 42.8° ± 1.3, indicating fair to excellent flow properties, with formulations F8 and F9 having the best flowability. The bulk densities of the blends ranged from 0.48 to 0.67 g/mL, and tapped densities ranged from 0.58 to 0.74 g/mL demonstrating consistent packing properties of the powder mixtures. Carr’s index (9.5-17.2 %) and Hausner ratio (1.10-1.21) further established satisfactory compressibility and flow properties. The flow was quite good for both F8 and F9, which had the lowest Carr’s index and Hausner ratio, suggesting less interparticulate friction and better packing amongst all formulations. Taken together, pre-compression data showed that all powder blends have good flow and compressibility characteristics, which are required for consistent die filling during tablet formulation.

Table 02: Pre compression Parameters

Weight variations:

The mean weights of the pharmacopeial limits of all formulations were identified to be within the acceptable range, with a variation of 399.5 1.6 mg (F3) through to 401.3 1.5 mg (F8). The close variation meant even fill of the die and the same flow of powder in compressing.

Thickness:

Tablet thickness was slightly different in 3.21 ± 0.04 mm (F1) to 3.35 ± 0.05 mm (F9), indicating that compressional force was constant and the distribution of materials showed to be the same across formulations. The growth in thickness was associated with the incorporation of more of the hydrophilic polymers.

Hardness:

Tablets were hard as 5.20 ± 0.30 kg/cm 2 (F1) to 6.40 ± 0.20 kg/cm 2 (F9). Progressive rise in hardness was used to show enhanced compactness and binding properties with enhanced polymeric matrix content especially because the polymeric Xanthan Gum and Chitosan were gel forming.

Friability:

All formulations were found to have good mechanical resistance with friability values of less than 1%. Friability of the tablets adopted a value of 0.32 ± 0.01% (F9) to 0.41 ± 0.02% (F1), and this confirmed that all the tablets were within the pharmacopeial specification of mechanical strength.

Disintegration Time:

There was a progressive increase in time of disintegration with polymer concentration between 22.4where F1 was 22.4100.8 and F9 was 88.5101.6. The formulations that included more Xanthan Gum and Chitosan in the formula disintegrated slower, which is in line with properties of forming matrices that inhibit penetration of water.

Swelling Index:

The swelling index in 8 hours was 45.6 ± 1.2% (F1) to 98.6 ± 1.5% (F5). The swelling behaviour was increased that indicated the hydrophilic and gelling ability of the polymers. Recipes with a combination of Xanthan Gum and Chitosan (F6–F9) were shown to have controlled and sustained swelling properties needed to release drugs over a longer period.

Drug Content Uniformity:

The formulations contained the following amount of drug: The drug content of the formulations fell within the pharmacopeial range, with F1 having 99.2 ± 0.8% of the claimed amount and F5 showing 99.7 ± 0.6% of the labelled amount. The small difference value reflected good mixing and dispersion of drugs in the formulations.

Table 03: Post compression Parameters

The in vitro drug release profiles of Celecoxib containing matrix tablets were examined over 8 hours, and the results are depicted in Table 04, and the release profile in fig 04. The release profiles were markedly different depending on the polymer type and combination. Formulation F1 with 120 mg Pullulan showed a quick dissolution-controlled release profile with complete drug release within 8 h. The hydrophilic property of Pullulan favoured matrix hydration and erosion, resulting in an initial burst followed by a concentration-dependent decline in release rate. Formulations F2 and F3, prepared with diverse Pullulan–Xanthan ratio exhibited a diffusion controlled mechanisms due to the gel formation inherent in Xanthan Gum retarded the drug movement across hydrated barrier. Release of the drug was fairly sustained, and was described by square-root-of-time dependency of Fickian diffusion. Out of all the formulations, formulation F4 (Pullulan 40 mg and Xanthan Gum 80 mg) showed highest sustained release behaviour with consistent drug release of 84 % at the end of 8 hours. The higher content of Xanthan imparted matrix strength and invariable swelling, therefore achieving an almost linear release during the investigation. However, it is seen that formulations F5–F9 with Xanthan and/or Chitosan displayed depressed release because of its high viscosity and pronounced gelation. F5 (with 120 mg of Xanthan Gum) and F6 to F8 with Chitosan having an intermediate release of the drug was reported, (67.9–85 %), which was controlled by both diffusion as well as erosion. Formulation F9 (prepared with equal ratio of Xanthan and Chitosan) evidenced erosion controlled kinetics as the dissolution proceeded because a prolonged deterioration in matrix surface area occurred, resulting to the slow release i.e. 80.5 % at 8 hr.

Table 04: In vitro Drug release

Fig 05: In vitro drug release study

Drug Release Kinetics:

In order to understand the mechanism of drug release, the dissolution data for each formulation were analysed and fit to Zero-order, First-order, Higuchi, Korsmeyer–Peppas and Hixson–Crowell kinetic models by correlating correlation coefficients (R² values) with best fitted equations as shown in Table 05. Formulation F1 showed the highest linearity (R² = 0.991) for a First-order model thereby indicating concentration-dependent release. F2, F3, and F5 exhibited greater linearity with Higuchi model (R² = 0.988–0.994), and indicated square root of time diffusion controlled release. The optimized batch F4 showed linearity (R² = 0.999) with the Zero-order model suggests uniform release rate irrespective of drug concentration. Formulations F6, F7 and F8 demonstrated a good Korsmeyer–Peppas model fit (R² = 0.992 to 0.996) with the release exponent n ranging between 0.55 and 0.68, indicating the drug was transported through anomalous (non-Fickian) transport mechanisms due to diffusion- and polymer-relaxation-controlled processes. The F9 was described to have the drug release mechanism governed by surface erosion as the matrix size decreased during dissolution best fitted with Hixson–Crowell model (R² = 0.989).

Table 05: Correlation Coefficient (R²) Values for Various Kinetic Models