Development of Nicotinic Acid Controlled Release Tablets with Natural Phenolic Anti-oxidant Polymer by Encapsulation Technique

Nicotinic Acid (NA) is a cholesterol lowering agent used to treat dyslipidemia. Proanthocyanidins (PC) was selected as a drug and encapsulation material in which the later has a dual property of being a polymer as well as cholesterol lowering agent. The encapsulation of NA with different concentrations of (PC) was carried out by solvent evaporation technique. The encapsulated NA was converted to granules which were then compressed into tablets by wet granulation method. It was subjected to many pre-compression parameters evaluation such as flow properties, drug content and encapsulation efficiency. The tablets were evaluated for thickness, hardness, friability, in vitro release studies, release kinetics and stability studies. The evaluated parameters of the formulations showed compliance with pharmacopoeial standards. The encapsulation efficiency was 99.73% and 99.52% of drug content. The FT-IR spectrum did not show interaction between drug and polymer. The drug release in pH 1.2 was lesser than in pH 6.8 buffer. The encapsulated product released drug in controlled manner in alkaline medium. The drug release was 97.1% and release was extended up to 12 hrs. The optimized batch underwent stability studies as per ICH guidelines. It can be concluded that among all the formulations the F5 can be considered as optimized formulation. The optimized formulations showed non-fickian diffusion mechanism of release. DOI: 10.18311/jnr/2020/25514


Introduction
There is an increase in the number of patients with chronic diseases off late., which necessitates taking drug for a longer time or multidrug together, which can lead to increase in non-compliance. The problem would be worse if half-life of drug is short. A dosage design offering gradual drug release might me one method to solve this problem. Controlled release dosage forms releases their active ingredients at a predetermined rate and time. The oral administration of pharmaceutical dosage forms is the more usual, convenient and comfortable route for active drug delivery to the body. Oral controlled release systems continue to be the most popular among the drug delivery systems since it has many advantages over the conventional systems. the dose (500-mg thrice daily) due to its short half-life (t1/2 = 1 to 3 h). After oral administration, NA is rapidly absorbed from the GIT. The associated side effects are increased level of plasma of NA immediately after oral administration. The patients suffer facial and truncal blushing (prostaglandin mediated) during initial treatment with plain NA or Immediate Release (IR) 3 . These symptoms decrease slowly, but unfortunately, most of the patients stop the treatment before the development of tolerance. There are many unwanted effects like itching, diarrhea and irritation of the mucous membrane irritation. Also, NA IR (immediate release) requires multiple -doses (2 or 3 times a day) 4 . In 1960s the Sustained Release (SR) tablets containing NA was formulated in order to reduce the flushing. But the clinical use of SR-NA showed more hepatotoxicity and gastrointestinal intolerance 5 . Hence to overcome the side-effects of NA-IR and NA-SR delivery system, the Controlled Release (CR) NA formulations would be efficient.
PC is a condensed tannin consisting of oligomers and polymers of monomeric flavans. They are present in several berries, red grapes and their wines, and seeds, baking chocolate, cinnamon, pycnogenol, and Ginkgo biloba 6,7 . They are present more in vegetables and fruits. It contains catechin, epicatechin, and gallic acid esters 8 . PC is a strong natural antioxidant, containing multiple hydroxyl groups, and has attracted a considerable research interest in pharmaceutical preparations 9,10 . The investigations of PC attracted the scientists due to its numerous pharmacological properties, including antioxidant 11 , anticancer 12 , antimicrobial 13 , antiangiogenic 14 , lipoprotein lowering agent, cholesterol lowering agent, anti-atherosclerotic agent 15 -17 and anti-inflammatory actions 18 . It has been reported that PC, even in high doses, is noncarcinogenic and nonteratogenic 19,20 . Encapsulation is a technique to entrap solids, liquids, or gases inside one or more polymeric coatings 21 . Microencapsulation protects the unstable core from its environment thereby improving its stability and extends the shelf life of core until its release 22,23 . One of the popular methods for the encapsulation of drugs is the solvent evaporation method. Hence PC polymer was used to develop control release system of NA, since PC itself is a lipoprotein (a) lowering agent, cholesterol lowering agent and an antiatherosclerotic agent. PC coupled with NA, doubled the desired effects simultaneously reducing the undesirable side effects of NA. Hence NA was chosen as a drug to develop a dissolution controlled system of NA by encapsulation with PC, a natural phenolic antioxidant polymer for the treatment of dyslipidemia.

Materials
Nicotinic acid was obtained from SD Fine Chemicals Ltd, Bangalore and Proanthocyanidine from MMC health care, Chennai. SLS, PVP K30, Starch, Magnesium stearate and Talc were obtained from KAPL, Bangalore. All the chemicals and reagents used were of analytical grade.

Preformulation Studies
The physicochemical characteristics of the drug and the drug in combination of excipients were investigated. These studies were initially performed before the development of dosage form.

Determination of Melting Point (Capillary Method)
One end of capillary tube was sealed and the fine powder of NA was filled in the other end, which was tied to a thermometer placed in Thais tube and placed on fire. The temperature at which the powder melted was noted.

Solubility
Solubility of NA was determined in pH 1.2 and 6.8 buffers spectrophotometrically (pH 1.2 blank at 260.5nm, pH 6.8 blank at 262.4nm).

Compatibility Studies
Compatibility study was carried out for the drug and its excipients by FTIR.

Encapsulation of NA with PC by Solvent Evaporation Method
Encapsulation of NA with PC by solvent evaporation method involved the following manner, the required quantity of PC (2% w/v) was dissolved in methanol and the active substance NA (250 mg) was dispersed uniformly into polymer solution with agitation. The resultant polymer and drug mixture was added manually drop wise at the rate of 1 ml/min into (3% w/v) sodium lauryl sulphate with agitation about 100 rpm and heat maintained at 100 °C. After addition of mixture, stirring was continued for 2 hours to achieve encapsulation of NA. The encapsulated NA was collected and dried in hot air oven at 40°C for 30 minutes to complete removal of moisture content. The different concentrations of polymer were used to estimate best drug release rate from dosage.

Drug Polymer Interaction (FTIR) Study
FT-IR spectroscopy was performed by Fourier transform infrared spectrophotometer. The drug and potassium bromide were compressed at 50 psi on KBr-press to form pellets. The spectra were scanned in the wave number range of 4000-600 cm -1 . FTIR study was carried on NA, physical mixture of NA and encapsulated NA.

Percentage Yield
Percentage yield was estimated to determine effectiveness of the method of preparation. Practical yield was calculated from the weight of the encapsulated nicotinic acid in comparison with the materials taken initially. The percentage yield of prepared encapsulated NA was determined.

Encapsulation Efficiency
Encapsulated NA (100mg) was powdered, dissolved in pH 6.8, sonicated for 30 minutes and filtered through 0.45μm membrane filter. The drug content was determined by UV spectrophotometer at 262 nm. The entrapment efficiency was calculated.

Formulation of Granules from Encapsulated NA
NA Granules containing the encapsulated NA was prepared by wet granulation technique with different concentrations of proanthocyanidin. Different steps followed for wet granulation are as follows, weighing of encapsulated NA, preparation of dump mass, screening the dump mass into granules, drying the granulation and sizing the granulation by dry screening. Specified quantity of encapsulated product was weighed. A 1%w/v PVP K30 was added to increase the cohesion. The resulting damp mass was used to prepare the granulation. Then it was pressed through the sieve (10 number) to prepare the granules manually. The prepared granules were spread uniformly on paper in trays and dried. Granules were dried in hot air oven at 60°C for 1 to 2 hours. The granules were sieved through number 20 sieve.

Evaluation of Pre-compression Parameters of Granules containing Encapsulated NA
The pre-compression parameters like angle of repose, bulk density and tapped density, Hausner's Ratio, Compressibility index (Carr's Index) were determined as per the standard protocol 25, 26 .

Formulation of Tablets of NA
The prepared granules were mixed with lubricants (magnesium stearate, talc) to avoid adhesion of tablet in punches and dies during compression ( Table 1). The granules were compressed by 16 stations automatic tablet punching machine (MK1 -16 stations punching machine (11mm concave punches).

Evaluation of Post-compression Parameters of NA Tablets
The prepared tablets were subjected to evaluation of properties including drug content uniformity, weight variation, tablet hardness, friability, thickness, disintegration study and in-vitro drug release with different media. The percentage of in-vitro drug release of NA from tablets was determined using the dissolution apparatus II of United States Pharmacopoeia (USP) XXIV, paddle type with 900 ml of pH 1.2 buffer at 37°C for initial two hours followed by pH 6.8 phosphate buffer for the remaining hours at 50 rpm. 5 ml sample solution was taken for 12 hours in regular intervals and replaced with fresh dissolution medium. The samples were diluted to suitable concentrations with respective dissolution medium. The absorbance was measured using a UV-Visible Spectrophotometer (UV-1800) and the cumulative drug release percentage was calculated.

Kinetic Analysis of In-vitro Release Rates of Controlled Release Tablets
The in-vitro release profile of all the formulations were subjected to the data analysis of various models namely zero order kinetic model, first order kinetic model, Higuchi's model, Korsmeyer equation and/or Peppa's model.

Stability Studies
The stability studies were carried out as per ICH guidelines. These studies were designed to elevate degradation of the drug (physical and/or chemical) with increased storage properties. The formulations were tested by storing at various conditions of temperature and humidity.

Preformulation Studies
Preformulation testing was performed for drug substances alone and with pharmaceutical excipients.

Determination of Melting Point
The melting point of NA was found to be in the range 236.4-236.6 °C which was compiled with BP standards, indicating purity of the drug sample.

Solubility
NA was found to be more soluble in pH 6.8 phosphate buffer as compare to pH 1.2 and pH 7.4 phosphate buffer, i.e. it has optimum solubility at pH 6.8 (4.67 mg/ml). The solubility decreased to about (2.56mg/ml) at pH 1.2 and it was equal to (3.28mg/ml) at pH 7.4.

Compatibility Studies
There were no chemical interactions between drug and the polymers. The FTIR spectra of mixture of drug and polymers (Figures 2, 3 and 4) did not show any changes in the main peaks, from which it is understood that there were no physical interactions. The peaks obtained in the spectrum of each polymer correlates with the peaks of drug spectrum (Table 3) which shows they are compatible.

Encapsulation of NA with PC by Solvent Evaporation Method
NA was encapsulated with PC by solvent evaporation method.

Evaluation of Encapsulated NA
The physical mixture of NA and encapsulated NA was compatible. The percentage yield was satisfactory and within the limit as per the standard protocol. The resulted efficiency of encapsulation of NA with PC was appreciable.     weight variation for all the formulations were within the standard limit. From the above data, formulation F-5 was selected as the optimized formulation.

Formulation of Tablets of NA
The granules were compressed in 16 stations punching machine containing 11 mm concave punches.

Evaluation of Post-compression Parameters of NA Tablets
The prepared NA tablets were evaluated for drug content uniformity, weight variation, tablet hardness, friability, thickness, disintegration study and in-vitro drug release 24 . The weight variation was found to be within the standard limits (Tables 6, 7). The thickness depended on the size of the die cavity, compression force and tablet weight. The thicknesses of the formulations were in the range of 4.14±0.0154 -64±0.036 mm and the hardness was in the range 6.6±0.179 -6.8±0.150 kg/cm 2 indicating good mechanical strength. Friability and drug content uniformity were found to be within official limits (Table 9). The dissolution studies were  carried out for 12 hours (Table 10 and Figures 5, 6). As per the result of dissolution study of formulation, F-4 and F-5 showed reasonable release of 91%, 97.23% respectively at the end of 12hrs. Formula F-5 has shown good drug release profile (97.23%) at 12 hours which showed excellent encapsulation integrity (Table 8) during the period of study when compared to the other formulations. Based on all these results, formulation F-5 was selected as the optimized formulation with 97.23% drug release.

Kinetic Analysis of in-vitro Release Rates of Controlled Release Tablets
The release kinetics were fitted to different mathematical models like Zero order, Higuchi's and Korsmeyer-peppa's    plot. The optimized Formulation F-5 followed Higuchi's plot since the regression coefficient is 0.833 which confirmed the drug release was through diffusion (Tables 12, 13  value for first order for F5 from which it was confirmed that the drug release followed zero order.

Stability Studies
The optimized batch, F-5 was subjected to stability studies as per ICH guidelines. The tablets did not vary in integrity of the matrix at all temperature, significant changes were not found in the drug content. The hardness, friability and drug release values were within the limits (Tables 14-16) even after 90 days.

Conclusion
NA is a potent cholesterol lowering agent used in the treatment of dyslipidemia. NA has short biological halflife of 1-3 hours. The dissolution controlled system was       developed for NA by encapsulating with natural phenolic antioxidant polymer. This approach is to achieve stable drug level in plasma with reduced fluctuations via slow drug release over an extended period of time The F4 and F5 formulations resulted in good drug release and encapsulation efficiency. But formulation F-4 showed the release percentage of 97.74% for 11 hours whereas F-5 with 97.23% for 12 hours. The drug release followed zero order release. The results suggested that the formulated controlled-release tablets of NA through encapsulation can be effective than the conventional dosage forms and also better patient compliance. Preclinical and clinical studies can be further performed in order to evaluate the efficacy of NA controlled release formulations for the management of dyslipidemia.

Acknowledgement
Authors are thankful to Management and Principal, T John College of Pharmacy, Bangalore and Karnataka Antibiotics Private Limited (KAPL), Bangalore for providing facilities to undergo the project.