Preparation and Evaluation of Zafirlukast Compression Coated Tablets for Chronotherapeutic Drug Delivery

The objective of the present study was to formulate and evaluate an oral, time-controlled drug delivery system of Zafirlukast. Zafirlukast belongs to BCS class II drugs as it has poor aqueous solubility and good permeability. Hence an attempt has been made to improve its aqueous solubility by solid dispersion technique so that its dissolution, bioavailability, and therapeutic effect can be optimized. The optimized solid dispersion was then formulated into a chronotherapeutic drug delivery system by compression coating technology. FT-IR study revealed that there was no chemical interaction between the drug and polymers used. Tablets were prepared by direct compression method using different super disintegrants and then followed by compression coating using natural polymers. Pre-compression and post-compression parameters complied with the Pharmacopoeia limit for the tablets. In vitro release studies were performed and the results indicated the formulation Z9F9 to be the optimized formulation.


INTRODUCTION
Oral drug delivery has been known for decades as the most widely utilized route of administration among all the routes that have been employed for the systemic delivery of drug via various pharmaceutical products of different dosage forms. The reasons that the oral route achieved such popularity may be in part attributed to its ease of administration [1]. The goal in drug delivery research is to develop formulations to meet therapeutic needs relating to particular pathological conditions. Research in the chronopharmacological field has demonstrated the importance of biological rhythms in drug therapy, and this brought a new approach to development of drug delivery system [2].
Chronotherapy considers a person's biological rhythms in determining the timing and amount of medication to optimize a drug's desired effects and minimize the undesired ones [3]. Coordinating biological rhythms with medical treatment is known as chronotherapy, which allows for appropriate dosing of actives at the most suitable times of the day, thus improving efficacy and reducing undesirable side effects [4].
The potential benefits of chronotherapeutics have been demonstrated in the management of a number of diseases like hypertension, asthma, allergic rhinitis, peptic ulcer disease, rheumatoid arthritis and related disorders which follow body's circadian rhythm. Administration of the most appropriate drug in the form of pulsatile delivery system wherein the delivery device is capable of releasing the drug after predetermined lag time could offer a more effective therapy providing maximum drug concentration at maximum intensity of disease condition. [5,6] Pulsatile drug delivery denotes the capability of a controlled release preparation to deliver the drug at varying rates from very low to high over a desirable time. Out of various timed release formulations available, compression-coated tablets gained wide attention. Compressioncoated tablets (CCT's) are composed of an inner core that contains an active pharmaceutical ingredient surrounded by an outer layer that slowly dissolves or disintegrates to make a lag time of drug release. A timed-release formulation could allow drug release and a greater plasma drug concentration at the point in the circadian cycle when clinical signs develop or increase. [7] Asthma is a chronic inflammatory disease of the airways, characterized by hyper responsiveness to a variety of stimuli. The role of circadian rhythms in the pathogenesis and treatment of asthma indicates that airway resistance increases progressively at night in asthmatic patients. Chronotherapy for asthma is aimed at getting maximal effect from bronchodilator medications during early morning hours [8].
The objective of the present study was to formulate and evaluate an oral, time-controlled drug delivery system of Zafirlukast (an oral leukotriene receptor antagonist that blocks the action of the cysteinyl leukotrienes on the CysLT1 receptors which is chemically designated based on chronopharmaceutical approach by the press (compression) coating technology using natural polymers for the treatment of nocturnal asthma. Zafirlukast, a BCS class II drug has poor aqueous solubility and good permeability. Hence, enhancement of its aqueous solubility has been attempted by means of solid dispersion technique [10]. . KBr pellets were prepared gently by mixing the 1 mg sample with 100 mg Potassium bromide.
a) Physical mixtures: Accurately weighed quantities of drug and polymer were taken in a glass mortar and mixed thoroughly. The resultant mixture was passed through sieve number 100 and was stored in a desiccator for complete removal of moisture.
b) Kneading method: The weighed quantities of drug and polymer at different ratios were taken in a mortar and triturated with a small volume of acetone. The obtained mass was kneaded for 45 min, dried in a desiccator for 48 hours. The dried product was pulverized, sifted through sieve number 100, and stored in a well-closed container, and kept in a desiccator.
c) Solvent evaporation method: Drug and polymer were mixed in different ratios in a mortar. Acetone was added proportionately with constant and continuous stirring until the mixture was completely dissolved. Acetone was evaporated under constant stirring and resultant solid dispersions were crushed, pulverized, and sifted through 100 mesh.

Formulation of Core Tablets of Zafirlukast by Direct Compression
The inner core/immediate-release tablets containing Zafirlukast were prepared by the direct compression method. As per the formulation variables shown in the Table: 2, the solid dispersions of Zafirlukast, microcrystalline cellulose and super disintegrant were dry blended for 15 min followed by the addition of talc and magnesium stearate. The mixtures were then further blended for 5 min. The resultant powder blends were then evaluated for flow properties like the angle of repose, bulk density, tapped density, Carr's index, and Hausner's ratio and finally compressed using a single punch CADMACH machine at a compression pressure of around 5-6 kg/cm² to obtain tablets of 6.0mm diameter and weighing 100mg each. The tablets were packed in aluminum foil, wrapped with brown paper.

Preparation of Compression-Coated Tablets of Zafirlukast
The press coated tablets of Zafirlukast (Z9F1-Z9F9) were prepared by compression coating of the optimized core tablet formulation (ZF9) with outer barrier layers of 400mg each having different compositions of polymers like xanthan gum, tamarind gum, locust bean gum, and dammar gum, the formulae of which are mentioned in the Table:3.  Croscarmellose Magnesium stearate 2 2 2 2 2 2 2 2 2 7. Before compression, the prepared polymer blends were evaluated for flow properties like the angle of repose, bulk density, tapped density, Carr's index, and Hausner's ratio. The core tablets were press-coated with 400mg of prepared barrier blend as per the mentioned formulae from Z1F9 to Z9F9. 200mg of barrier layer material was weighed and transferred into a 10mm die and then the core tablet was placed manually at the center. The remaining 200mg of the barrier layer material was added into the die and compressed.

Evaluation of Solid Dispersions a) Drug entrapment efficiency [13]
The drug content in the solid dispersion was determined spectrophotometrically. An accurately weighed sample of solid dispersion equivalent to 10 mg of Zafirlukast was dissolved in 10 ml of acetone. The solution was filtered, suitably diluted with distilled water with 0.5% SLS and the absorbance was measured at 230 nm. The drug content was calculated from the calibration curve and expressed as percent entrapment efficiency as explained in the equation below- Dissolution studies of pure drug and all the solid dispersions of Zafirlukast were carried out using USP type II dissolution apparatus (paddle type) by using 900ml of distilled water with 0.5% SLS as the dissolution medium at a speed of 50rpm and a temperature of 37±0.5°C. 5ml samples were withdrawn through a filter of 0.45μm at different time intervals, suitably diluted, and assayed for Zafirlukast by measuring absorbance at 230 nm.

Evaluation of Core Tablets [14,15,16]
All the prepared core tablets were optimized by average weight, hardness, friability, thickness, drug content, disintegration time, wetting time, and in vitro dissolution for further conversion of selected core tablet in the form of compressioncoated tablets of Zafirlukast.

Average weight
Average weight was carried out for 20 tablets selected at random from the batch containing 100 tablets. The results are given in Table: 7.

Hardness
Hardness was determined by Monsanto hardness tester.

Friability
The friability of 20 tablets was determined by Roche friabilator at 25 rpm for 4 min.

Thickness
Thickness was measured by vernier calipers.

Drug content
Drug content was determined by weighing and grinding 10randomly selected tablets and dissolving powder equivalent to 10 mg of the drug in 100 ml of distilled water with 0.5% SLS.
The solution was then sonicated for 5 min and then filtered through a 0.45µ membrane filter. The absorbance of this solution was determined at 230 nm and drug content was calculated.

Disintegration time
The in vitro disintegration studies were carried out using a digital tablet disintegration test apparatus. One tablet was placed in each of the 6 tubes of the basket assembly and then a disk was added to each tube. This assembly was then suspended in a 1-liter beaker containing water with its temperature being maintained at 37±2°C. The basket was then moved up and down through a distance of 5 to 6 cm, at the frequency of 28 to 32 cycles per minute. The time required for the complete disintegration of the tablet was recorded. It is expressed in seconds.

In vitro dissolution rate studies
In vitro release rate studies of the core tablets were performed using the USP type II apparatus (paddle type) by using 900ml of distilled water with 0.5% SLS as the dissolution medium at a speed of 50rpm and a temperature of 37±0.5°C. 5ml samples were withdrawn through a filter of 0.45μm at different time intervals, suitably diluted, and assayed for Zafirlukast by measuring absorbance at 230 nm.

Wetting time
A tissue paper folded twice was placed in a Petri dish. 10ml of water is added to the Petri dish. A tablet was carefully placed on the surface of the tissue paper. The time required for water to reach the upper surface of the tablet was noted as wetting time.

Evaluation of compression-coated tablets
All the prepared compression-coated tablets were evaluated for average weight, hardness, friability, thickness, swelling index, and in vitro dissolution.

% Swelling Index [16]
The tablets were weighed and placed in a Petri dish containing 10ml of dissolution medium. At specified time intervals, the tablets were removed, lightly blotted with tissue paper to remove excess liquid, and then weighed. The swelling index was calculated using the formula, Swelling index (%) = [W s -W d /W d ] * 100 Where W s = weight of swollen tablet at a time' W d = weight of the dry tablet

In vitro dissolution rate studies
In vitro release rate studies of the press coated tablets were performed using the USP type II apparatus (paddle type) by using 900ml of distilled water with 0.5% SLS as the dissolution medium at a speed of 50rpm and a temperature of 37±0.5°C. 5ml samples were withdrawn through a filter of 0.45μm for every hour up to 10 hours and the lag time was observed for every batch of tablets. The withdrawn samples were analyzed spectroscopically by measuring the absorbance at 230nm.

Drug-Excipient Interaction Studies
The FTIR spectrum of Zafirlukast sodium exhibited a peak at 3443.98cm -1 due to N-H stretching and at 1616.51cm -1 due to SO 2 stretching.
There was no interference of the functional group as the principal peaks of the Zafirlukast were found to be unaltered in the final optimized formulation, indicating they were compatible chemically.

Drug entrapment efficiency
From the drug entrapment values it was observed that solid dispersions prepared with the solvent evaporation method were better entrapped compared to physical mixing and kneading methods.

In vitro drug release studies
All the solid dispersions of Zafirlukast were subjected to in vitro drug release studies to select the optimized formulation possessing an increased in-vitro dissolution rate. The dissolution profiles of Zaf: PEG 15000 solid dispersions were shown in Fig. 3,4 and 5. The dissolution rate of Zafirlukast was found to be increased in all the solid dispersions prepared by physical mixing, kneading, and solvent evaporation methods in comparison to the dissolution rate of pure drug. The solid dispersions prepared by the solvent evaporation method exhibited better dissolution profiles than those prepared by physical mixing and kneading methods. Amongst all the solid dispersions of Zafirlukast, the formulation PF15 prepared by the solvent evaporation method in Zaf: polymer ratio of 1:2.5 was found to possess the highest dissolution rate of 95.69% in 60 min (Fig. 5). The increased dissolution rate may be due to the higher solubility of PEG 15000 in the dissolution medium and the better wettability of Zafirlukast in the conjugate.

Evaluation of Immediate Release
Core Tablets

Pre-compression parameters
Powder blends used for preparing immediate release core tablets (ZF's) were evaluated for angle of repose, bulk density, tapped density, Hausner's ratio, Carr's index, The values for the angle of repose, Hausner's ratio, and compressibility index were found to be in good correlation, indicating that all the formulations possess passable flow property and compressibility.

Post-Compression Parameters
The prepared core tablets were evaluated, and were found to exhibit satisfactory tablet characteristics as shown in Table 7 and 8. The drug content of all the formulations was found to exist between 90 and 100% and formulation ZF9 was found to be within the USP limits as per the drug content. The in vitro disintegration time and wetting time were found to be very less for ZF9formulation that is 58 seconds and 23 seconds respectively and this batch tablets have also shown better dissolution profile (99.85% drug release in 25 minutes) when compared to remaining formulations. Hence, it was optimized as the best immediate release core tablet formulation for the burst release of the drug. The results of the dissolution profiles of all the formulations (ZF1-ZF9) were represented graphically in Fig. 6.

Evaluation of polymer layer blends
The polymer layer blends of all the compressioncoated tablet formulations (Z1F9-Z9F9) were evaluated for flow properties and it was found that the flow property of the prepared polymer layer blend of Z4F9 and Z5F9 was good, that of Z1F9 and Z2F9 was fair, Z3F9, Z8F9, and Z9F9 have passable flow properties whereas the flowability of remaining blends was poor.

Evaluation of compression-coated tablets
The prepared compression-coated tablets were evaluated for all the post-compression parameters and were found to exhibit satisfactory tablet characteristics. The swelling index was found to be maximum at the 5 th hour for the formulation Z9F9. The results were tabulated in table: 10 and 11.
From the results of in vitro drug release studies (Table: 12), it can be seen that all the press coated tablets showed distinct lag times (Fig. 7). The formulations Z1F9 to Z8F9 showed a lag time of 4 hrs with drug release extending up to 10 hours but are not consistent with the demands of chronotherapeutic drug delivery. The formulation Z9F9 with the barrier layer composition of xanthan gum and dammar gum showed the pre-expected lag time of 5 hours with a considerable drug release of 98.89% for 3 hours. Hence, this formulation was selected as the optimized formulation for further studies.  parameters such as drug entrapment efficiency, flow properties, hardness, friability, weight variation, drug content, wetting time, swelling index, in vitro drug release rate were evaluated for all the formulations. The formulation Z9F9 containing xanthan gum and dammar gum as the barrier layer for retarding the release of the drug from the tablet was found to exhibit the results which are consistent with the demands of chronotherapeutic drug delivery. In conclusion, it can be suggested that the combination of xanthan gum and dammar gum in the optimized composition could be promising in achieving chronotherapeutic benefits in asthma patients.

DISCLAIMER
The products used for this research are commonly and predominantly use products in our area of research and country. There is absolutely no conflict of interest between the authors and producers of the products because we do not intend to use these products as an avenue for any litigation but for the advancement of knowledge. Also, the research was not funded by the producing company rather it was funded by personal efforts of the authors.

CONSENT
It is not applicable.

ETHICAL APPROVAL
It is not applicable.