Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2225  Research Paper

Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Direct Compression and Sublimation Methods

Bolmal U.B1*, Pandey C.K1, Phatarpekar V2, Dhople N.G1 and Kotha Rajkumar1 1Department of Pharmaceutics, KLE University’s College Of Pharmacy, Belgaum -590010, Karnataka, India, and 2Themis Medicare Ltd., Haridwar, UP, India.

Received May 21, 2013; accepted May 30, 2013 ABSTRACT

Dispersible tablets are gaining popularity over conventional tablets due to its increased popularity for administration to pediatric and geriatric patients as it provides quick onset of action and ease of administration. An attempt had been made, to develop dispersible tablet of isoniazid and rifampicin combination by direct compression and sublimation method, to increase the bioavailability of the anti-tubercular agents as well to provide the local delivery in the case of oral tuberculosis. Formulation F1 to F8 (2% and 4% w/w of different superdisintegrants (crospovidone, pregelatinized starch, croscarmellose sodium and sodium starch glycolate) formulated by direct compression method. The formulations containing 4% of superdisintegrants (F2, F4, F6, and F8) were selected as optimized and hence 4% of superdisintegrants were used for sublimation method (F9 to F12). The effects of

sublimating material (camphor) on drug release profile and disintegration property were evaluated. Studies on two different methods showed sublimation method as a better alternative as its formulations rapidly disintegrates, disperse and shows faster drug release (in 14 min) in comparison to direct compression (in 20 min). Pre-compression parameters of formulation blends indicated good flow properties and compressibility. Simultaneous estimation was performed for calculation of drug content and % drug release. In vitro release data analysis revealed 90% drug release. F9 formulation (sublimation) showed best anti-tubercular activity. F2, F9 formulations were found to be stable even after 90 days. Hence it is evident from this study that fast dissolving tablets could be a promising delivery system for isoniazid and rifampicin with improved drug availability and better patient compliance.

KEYWORDS: Direct compression; sublimation; tuberculosis; superdisintegrants; anti-tubercular activity; simultaneous estimation.

Introduction

Oral drug delivery has been known for decades as the most widely utilized route of administration among all the routes that have been explored for the systemic delivery of drugs via various pharmaceutical products of different dosage forms (Amin and Kohli, 2003). Despite all the advantages, conventional tablets generally do not prove useful in situations, Where in elderly persons face difficulties in swallowing (dysphasia), conventional oral dosage forms (solutions, suspensions, tablets, capsules) because of hand tremors and dysphasia in children because of their under developed muscular and nervous system (Yeola et al., 2000; Mizumoto et al., 2005; Kuchekar et al., 2003 and Chang et al., 2000).

These problems led to the development of novel type of solid oral dosage forms called fast-dispersible tablets, which disintegrate and dissolve rapidly in saliva without the need of drinking water. They are known as fast dispersible tablets, melt-in-mouth tablets, rapid melts, mouth dissolving tablets, quick dissolving or rapidly

disintegrating tablets (Piet et al., 1993; Bandari et al., 2008). However, of all the above terms, United States Pharmacopoeia (USP) approved these dosage forms as ODTs. In such cases, bioavailability of drug is significantly greater than those observed from conventional tablet dosage form by avoiding first pass liver metabolism (Chein, 1992; Coetzee and Manomed, 1996). United States Food and Drug Administration (FDA) defined ODT as “A solid dosage form containing medicinal substance or active ingredient which disintegrates rapidly within a matter of seconds when placed upon tongue.” Recently, European Pharmacopoeia has used the term orodispersible tablet for tablets that disperses rapidly and within 3 min in mouth before swallowing (Bandari et al., 2008).

Tuberculosis is an infectious disease caused by the Mycobacterium tuberculosis. Although the primary infection site always involves the lungs, other organ systems are also susceptible. Tuberculosis is usually chronic and may be almost lifelong. Despite the advancement of the therapeutic methods in both the

 

International Journal of Pharmaceutical Sciences and Nanotechnology

Volume 6 •  Issue 4 • December 2013 (extra issue) IJPSN-5-21-13-BOLMAL

ABBREVIATIONS: ODTs --Oral dispersible tablets, UV—Ultraviolet, RH--Relative Humidity, IP--Indian Pharmacopoeia, PBS—Phosphate buffer saline.

2225

2226 Int J Pharm Sci Nanotech Vol 6; Issue 4 • December 2013 (extra issue)  prevention and treatments of this infection, tuberculosis still remains as a major cause of mortality and morbidity throughout the world particularly in many underdeveloped countries of Latin America, Asia and Africa (Herfindal et al., 1992). An adequate drug administration is the backbone of tuberculosis treatment and the selection of an effective chemotherapeutic strategy is essential. Rifampicin, isoniazid, pyrazinamide, streptomycin and ethambutol are the few common anti-tubercular agents. The most important requirement is using a dosage form of combining at least two or more drugs in order to prevent the emergence of the multi-drug resistance tubercular bacilli (MDR-TB) which is caused by inconsistent and partial treatment (Peto and Matthews, 1996; Mqoqi et al., 1997; Herfindal, 1992; Henry, 1993; Kochi, 1997; Coetzee and Manomed, 1996). The main objective of this study was to develop dispersible tablet of isoniazid and rifampicin combination by direct compression and sublimation method, to increase the bioavailability of the anti-tubercular agents as well to provide the local delivery in the case of oral tuberculosis. The formulations were prepared by using a blend of superdisintegrants such as crospovidone, sodium starch glycolate, pre-gelatinized starch and croscarmellose sodium. The main objectives of the study were to investigate the performance of superdisintegrants and effect of other process variables on the characteristics of the isoniazid and rifampicin combination dispersible formulations, as well as evaluate the in vitro performance of the formulations

Materials and Methods Drugs and Chemicals

All the materials were provided from Themis Medicare Ltd., Haridwar (U.K.). The materials of either AR/LR grade were used.

Preformulation Studies

Preformulation testing is the first step in the rational development of dosage forms of a drug. It can be defined as an investigation of physical and chemical properties of drug substance, alone and when combined with excipients.

Determination of melting point

Melting point of isoniazid and rifampicin was determined by capillary method.

Solubility study

Solubility analysis of isoniazid and rifampicin were carried out using different solvents like water, methanol, ethanol, acetone chloroform, ether and phosphate buffer pH 6.8 / 7.4.

Physical compatibility study

Drug and excipients were taken in the ratio of 1:1 and the vials were stored in the stability chamber at 40 ºC/75

% RH, 25 ºC/60 ºC and 2-4 ºC. These samples were checked for physical changes every week for a month.

Determination of λ-max of both drugs

Solution containing 10 µg/ml of isoniazid and rifampicin was prepared separately and scanned over wavelength range of 400- 200 nm. Wavelength at which highest absorbance was observed and recorded.

Simultaneous estimation of isoniazid and rifampicin in pH 6.8 phosphate buffer

Preparation of stock solutions

Standard stock solution (100 µg/ml) of isoniazid was prepared in phosphate buffer pH 6.8. Similarly, standard stock solution of rifampicin (100 µg/ml) was also prepared.

Preparation of standard solutions of isoniazid and rifampicin

From the above prepared Standard stock solution of isoniazid and rifampicin (100 µg/ml) different aliquots of various concentrations (5, 10, 15, 20, 25, 30, 35 µg/ml) were prepared using phosphate buffer pH 6.8. The absorbance was measured at 263 nm λmax for isoniazid and 263 nm and 333 nm λmax for rifampicin, against phosphate buffer pH 6.8 as blank. The linearity of the solutions was in the concentration range of 5-50 µg/ml for both isoniazid and rifampicin.

Preparation of mixed standard of isoniazid and rifampicin

Seven mixed standards with different concentrations 5, 10, 15, 20, 25, 30, 35 µg/ml of isoniazid and 5, 10, 15, 20, 25, 30, 35 µg/ml of rifampicin were prepared in phosphate buffer pH 6.8. As both compounds do not interact chemically in Phosphate buffer, two wavelengths, 263 and 333 nm were selected for estimations. The absorbance at these two sampling points was used to determine the concentrations of the two drugs in presence of the each other i.e. the absorbance of mixed standard was taken at 263 nm and 333 nm.

Simultaneous estimation

Based on property of additivity of absorbances

The two wavelengths on the rifampicin (263, 333 nm) curve were found out where it showed same absorbance. At 333 nm rifampicin showed maximum absorbance where isoniazid showed zero absorbance.

Mixed slandered solutions of different concentrations were then scanned. The calibration curves were plotted against respective absorbance at 333 nm for rifampicin. The absorbance for determination of isoniazid was taken as A1 = A263 – A333 (Kakade et al., 2002; Goyal and Panday, 2002).

Where, A1 is the absorbance difference taken for plotting calibration curve of isoniazid. A263 is the absorbance contribution by both drugs i.e. mixture at

Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2227  263 nm and A333 is the absorbance by rifampicin (where isoniazid shows zero absorbance) at 333 nm.

Formulation of dispersible tablets of isoniazid and rifampicin by two different methods

Direct compression method

Totally eight formulations (F1-F8) were prepared as given in the table 1. All the ingredients were passed through 60 mesh sieve separately (Lachman et al., 1987). The mixture was than compressed into tablets using a tablet compression machine (Rimek Mini press I, Ahmedabad) equipped with flat faced 11 mm punches.

Sublimation method

From formulations F1 to F8 (2% and 4% of different superdisintegrants) formulated by direct compression method, the formulations containing 4% of superdisintegrants (F2, F4, F6, F8) were selected as optimized and hence 4% of superdisintegrants were used for sublimation method.

Accurately weighed quantities of excipients as given in the table 2 were passed through 60 mesh sieve separately; volatile component camphor and diluents were mixed. The mixture was than compressed into tablets using a tablet compression machine (Rimek Mini press I, Ahmedabad) equipped with flat faced 11-mm

punches. After compression the tablets were heated in hot air oven at 60˚C until constant weight was obtained to ensure the complete removal of volatile component (Kumar et al., 2009).

Evaluation parameters of the formulations

Pre-compression parameters

Angle of repose (θ)

Funnel method was used to measure the angle of repose of blends. The accurately weighed blends were taken in a funnel. The height of the funnel was adjusted in such a way that the tip of the funnel just touched the apex of the heap of the blends. The blends were allowed to flow through the funnel freely onto the surface. The diameter of the powder cone was measured and angle of repose was calculated using following equation. Limits are shown in table 3 (Subramanyam, 2001).

tan θ = h/r

θ= tan-1 h/r

Where, h - height of the pile,

r - Radius of the pile.

TABLE 1

Formulation ingredients of dispersible tablets by direct compression

Ingredients (mg/tab) F1 F2 F3 F4 F5 F6 F7 F8 Isoniazid 100 100 100 100 100 100 100 100 Rifampicin 100 100 100 100 100 100 100 100 Cros-Povidone 8 16 - - - - - - Pregelatinized starch - - 8 16 - - - - Cros carmellose Sodium - - - - 8 16 - - Sodium starch glycolate - - - - - - 8 16 Micrcrystalline cellulose 120 112 120 112 120 112 120 112 Mannitol 54 54 54 54 54 54 54 54 Magnesium Stearate 3 3 3 3 3 3 3 3 Aerosil 5 5 5 5 5 5 5 5 Sucrolose 2 2 2 2 2 2 2 2 Talc 2 2 2 2 2 2 2 2 Flavour (Rospberry) 6 6 6 6 6 6 6 6 Total weight (mg) 400 400 400 400 400 400 400 400

TABLE 2

Formulation ingredients of dispersible tablets by sublimation methods

Ingredients (mg/tab) F9 F10 F11 F12 Isoniazid 100 100 100 100 Rifampicin 100 100 100 100 Cros-Povidone 16 - - - Pregelatinized starch - 16 - - Cros carmellose Sodium - - 16 - Sodium starch glycolate - - - 16 Camphor 30 30 30 30 Micrcrystalline cellulose 120 112 120 112 Mannitol 54 54 54 54 Magnesium Stearate 3 3 3 3 Aerosil 5 5 5 5 Sucrolose 2 2 2 2 Talc 2 2 2 2 Flavour (Rospberry) 6 6 6 6 Total weight (mg) 430 430 430 430

2228 Int J Pharm Sci Nanotech Vol 6; Issue 4 • December 2013 (extra issue)  TABLE 3

Relationship between angle of repose (θ) and flow properties

Angle of Repose (°) Flow properties <25 Excellent

25-30 Good 30-40 Passable >40 Very poor

Bulk density and tapped density

2 gram of powder from each blend was taken into a 10 ml measuring cylinder. After the initial volume was observed, the equipment was on and the cylinder was allowed to fall under its own weight. The reading of tapping was continued until no further change in volume was noted (Subramanyam, 2001).

BD = (Weight of Powder/Volume of the packaging)

TD = (Weight of powder/Volume of Packaging after tapping)

Carr’s index

The simplest way of measurement of free flow of powder is compressibility, which is an indication of the ease with which a material can be induced to flow. Limits are shown in table 4 (Subramanyam, 2001). It is given by compressibility index (I) which was calculated as follows,

I = Tapped density-Bulk density / Tapped density × 100

TABLE 4

Grading of the powders for their flow properties according to Carr’s index and Hausner’s ratio

Carr’s Index (%) Flow Character Hausner’s Ratio < 10 Excellent 1.00–1.11

11–15 Good 1.12–1.18 16–20 Fair 1.19–1.25 21–25 Passable 1.26–1.34 26–31 Poor 1.35–1.45 32–37 Very poor 1.46–1.59 >38 Very, very poor >1.60

Hausner’s ratio

The Hausner’s ratio is an indirect index of ease of powder flow. Limits are shown in table4 (Subramanyam, 2001). It was calculated by following formula,

Hausner’s ratio = Tapped Density/ Bulk Density

Post compression parameters

Thickness and diameter

Ten tablets were randomly selected from each batch and their thickness and diameters were measured by using vernier calipers (Gerbino, 2005). The average thickness and diameter with standard deviation of the tablets from each batch were calculated and tabulated.

Hardness test

Hardness was measured by using hardness tester (Pfizer hardness tester). From each batch, ten tablets were selected randomly and evaluated, the mean and standard deviation values were calculated (United States Pharmacopoeia, 2007).

Friability test

Compressed tablets should not lose more than 1% of their weight. % Friability of tablets less than 1% are considered acceptable (Indian pharmacopoeia, 2007).

F = initial final

initial

W – W×100

W

Weight variation test

Twenty tablets were selected randomly from each batch and weighed individually to check for weight variation, average weight were calculated. Not more than two of the individual weights deviate from the average weight by more than the 5% and none deviates by more than twice of this percentage.

A little variation is allowed in the weight of a tablet by I.P. The allowed percentage deviation in weight variation is given in table 5 (Indian pharmacopoeia, 2007).

TABLE 5

Limits for weight variation

Average weight of a tablet Percentage deviation 80 mg or Less ±10 More than 80 mg but less than 250 mg ±7.5 250 mg or More. ±5

Drug content uniformity

Twenty tablets of each formulation were taken randomly and triturated using glass mortar and pestle (United States Pharmacopoeia, 2007). The blend equivalent to 10 mg drug of each isoniazid and rifampicin was weighed and diluted suitably with phosphate buffer pH 6.8 and analyzed spectrophotometrically at 263 nm and 333 nm. The amount of isoniazid and rifampicin were estimated by using standard calibration curves (Kakade et al., 2002; Goyal and Panday, 2002).

Uniformity of dispersion

This test is applicable only for dispersible tablets. One tablet was placed in 100 ml of water and stirred gently until completely dispersed. A smooth dispersion was obtained which passes through a sieve screen with a nominal mesh aperture of 710 µm (Indian pharma-copoeia, 2007).

In-vitro dispersion time

Tablet was placed in 10 ml phosphate buffer solution, pH 6.8. Time required for complete dispersion of a tablet was measured and referred as dispersion time (Lourenço et al., 2007).

In-vitro disintegration time

The in-vitro disintegration time of a tablet was determined using disintegration test apparatus as per IP specifications. One tablet was placed in each of the 6 tubes of the basket. Add a disc to each tube and run the apparatus using phosphate buffer pH 6.8 maintained at 37 ± 2 °C as the immersion liquid. The time in seconds taken for complete disintegration of the tablet with no

Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2229  palpable mass remaining in the apparatus was measured and recorded (Indian pharmacopoeia, 2007).

In-vitro dissolution studies

In-vitro release study was performed using tablet dissolution test apparatus USP XXIII, apparatus II. The dissolution medium consisted of 900 ml phosphate buffer pH 6.8 containing 0.02% w/v ascorbic acid, maintained at 37 ± 1°C rotated at 50 rpm. At a time interval of 2 min, 10 ml sample was withdrawn and replaced with fresh medium. 10 ml sample was diluted to 100 ml phosphate buffer pH 6.8, the aliquots were assayed spectrophotometrically at 263 nm and 333 nm (United States Pharmacopoeia, 2007; Hiremath and Saha, 2008).

Comparison of formulation with marketed product

The promising formulations (F2 and F9) were compared with marketed (R-Ciinex kid containing 100 mg isoniazid IP and 100 mg rifampicin IP) formulation by comparing in vitro drug release.

Anti-tubercular activity

The anti-mycobacterial activities of optimized formulations (F2 and F9) and marketed formulation were assessed against M. tuberculosis were assessed using microplate Alamar Blue assay (MABA).

Briefly, 200 µl of sterile deionzed water was added to all outer perimeter wells of sterile 96 wells plate to minimized evaporation of medium in the test wells during incubation. The 96 wells plate received 100 µl of the Middlebrook H37 RV broth and serial dilution of compounds were made directly on plate. The final drug concentrations tested were 100 to 0.8 µg/ml. Plates were covered and sealed with parafilm and incubated at 37ºC for five days. After this time, 25 µl of freshly prepared 1:1 mixture of Almar blue reagent and 10% tween 80 was added to the plate and incubated for 24 hrs. A blue color in the well was interpreted as no bacterial growth, and pink color was scored as growth. The MIC was defined as lowest drug concentration which prevented the color change from blue to pink (Sudheendra et al., 2012; Lourenço et al., 2007; Franzblau et al., 1998 and Cassano et al., 2012).

Stability studies In the present study, Stability studies were done

according to ICH guidelines to assess the drug and

formulation stability. Optimized formulations were subjected to stability study at 40 ± 2ºC / 75% ±5% RH for 90 days. The samples were evaluated for physical changes, hardness, friability, in vitro dispersion, drug content and percentage drug release during the stability studies (Lucas and Bishara, 2004; Amin and Kohli, 2003).

Results and Discussion Preformulation studies

Determination of melting point

Melting point of isoniazid and rifampicin were found to be 172ºC and 190ºC which is in the range of 170-174°C and 187-190°C respectively as reported in literature.

Solubility study

Isoniazid sample was found to be freely soluble in water, soluble in phosphate buffer pH 6.8/7.4, sparingly soluble in ethanol (95%), slightly soluble in chloroform, very slightly soluble in ether.

Rifampicin sample was found to soluble in chloroform and methanol, slightly soluble in acetone, ether and in water, sparingly soluble in phosphate buffer pH 6.8/7.4.

Physical compatibility study

The samples stored in vials were checked every week for physical changes (colour) and no changes were observed, hence all ingredients were physically compatible.

Determination of λ-max of both drugs

For isoniazid λ-max was found to be 263 nm and for rifampicin it was found to be 263 and 333 nm.

Simultaneous estimation of isoniazid and rifampicin in pH 6.8 phosphate buffer

The overlain spectrum of isoniazid and rifampicin was found to be appropriate for the estimation of both the drugs. Based on the point of maximum absorbance the λmax of isoniazid were at 263 nm and for rifampicin were found to be at 333 nm and 263 nm.

The absorbance values were shown in table 6. Standard plots of isoniazid and rifampicin were showed in figure 1, 2, 3.

TABLE 6

Concentration and absorbance obtained for standard plot of isoniazid, rifampicin and mixed standard in phosphate buffer pH 6.8

Concentration (µg/ml)

Absorbance Pure Mixed For calculations

Isoniazid (263nm) A1

Rifampicin (263nm) A2

Mixed standard (263nm) A3

Mixed standard (333nm)A4

Rifampicin (333nm) A5

Isoniazid A6 =A3-A5

0 0 0 0 0 0 0 5 0.161±0.0020 0.131±0.0006 0.340±0.0010 0.133±0.0006 0.144±0.0010 0.196 10 0.296±0.0011 0.271±0.0015 0.642±0.0011 0.282±0.0015 0.287±0.0006 0.355 15 0.462±0.0015 0.398±0.00006 0.899±0.0010 0.406±0.0030 0.420±0.0010 0.479 20 0.605±0.0056 0.536±0.0038 1.147±0.0459 0.554±0.0027 0.543±0.0006 0.604 25 0.740±0.0015 0.662±0.0010 1.431±0.0025 0.679±0.0006 0.681±0.0006 0.750 30 0.911±0.0031 0.789±0.0015 1.687±0.0020 0.786±0.0021 0.798±0.0012 0.889 35 1.026±0.0061 0.899±0.0015 1.998±0.0010 0.919±0.001 0.921±0.001 1.077

UV absorbance values are expressed in mean±standard deviation (n=3)

2230 Int J Pharm Sci Nanotech Vol 6; Issue 4 • December 2013 (extra issue)  

Fig. 1. Standard calibration curve of isoniazid at 263 nm.

Fig. 2. Standard calibration curve of rifampaciin at 333 nm.

Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2231  

Fig. 3. Standard calibration curve of isoniazid for calculations.

Formulation of dispersible tablets of isoniazid and rifampicin by two different methods

Dispersible tablets of isoniazid and rifampicin were prepared. The prepared dispersible tablets were subjected to physiochemical evaluations.

Characterization and evaluation of the formulations

Pre compression parameters

Angle of repose (θ )

The results obtained for angle of repose of all the formulations were tabulated in table 7. The values were found to be in the range of 27°.455�± 0.6111 to 30°.159� ± 0.7361 which indicates good flow property of the blends.

Bulk density and tapped density

Both bulk density and tapped bulk density results were tabulated in table 7. The loose bulk density and tapped bulk density for all the formulations ranged from 0.499 ± 0.0038 g/cm3 to 0.560 ± 0.0019 g/cm3 and 0.582 ± 0.0064 g/cm3 to 0.657 ± 0.0036 g/cm3 respectively.

Carr’s index

The percent compressibility for the entire formulations lie within the range of 10.440 to 15.161 as tabulated in table 7. The results for all the formulation blends were found to be within the acceptable range.

Hausner’s ratio

The Hausner’s ratio for all the formulations lies within the range of 1.117 to 1.179 as given in table 7. All formulation blends showed improved flow properties.

Post compression parameters

Thickness and diameter

The thickness and diameters of the formulated tablets were found to be in the range of 3.334 ± 0.0413 mm to 3.632 ± 0.0779 mm and 11.043 ± 0.0094 mm to 11.061 ± 0.0143 mm respectively and reported in table 8.

Hardness test

Hardness was found to be in the range of 3.250 ± 0.1080 kg/cm2 to 3.95 ± 0.2549 kg/cm2 as tabulated in table 8. The obtained results revealed that the tablets have good hardness.

Friability test

Friability for all the formulations (F1-F12) was found to be in the range of 0.122 ± 0.0211 to 0.189 ± 0.0569 tabulated in table 8. The obtained results were <1% which indicated that the dispersible tablets of F1 –F12 formulations were within the I.P specifications and possessed good mechanical strength.

Weight variation test

All the tablets passed weight variation test as the % weight variation was within the IP limits of ±5.0 %. It was found to be in the range 399.87 ± 1.2394 mg to 400.958 ± 1.7456 mg as shown in the table 8.

Content uniformity

To evaluate a tablet’s potential for efficacy, the amount of drug in the tablet needs to be monitored from tablet to tablet and batch to batch. The mean drug content was carried out in triplicate and was found to be between 98.022 ± 1.39936 mg to 100.195 ± 0.3980 mg

2232 Int J Pharm Sci Nanotech Vol 6; Issue 4 • December 2013 (extra issue)  for isoniazid and 98.012 ± 0.4443 mg to 101.769 ± 0.3846 mg for rifampicin respectively as given in table 9.

Uniformity of dispersion

All the formulations passed through sieve no 22 which indicates a uniform dispersion.

In-vitro dispersion time

Rapid dispersion within seconds has been observed in all the formulations. The values were found to be in range and are mentioned in table 9.

In-vitro disintegration time

Internal structure of the tablets that is pore size distribution, water penetration into tablets and swelling of disintegrants are suggested to be the mechanisms of disintegration. The results were found to be in the range of 21.297 ±0.9404 sec and 51.590 ± 0.4187 sec tabulated in table 9. Among the four superdisintegrants used, crospovidone showed less disintegration time followed by pregelatinized starch, croscarmellose sodium and finally sodium starch glycolate and formulations prepared by sublimation method showed faster disintegration.

TABLE 7

Micrometric properties of mixed blend and excipients

Formulation code

Angle of repose(°) (Mean ± SD)

Bulk density (gm/cm3) (Mean ± SD)

Tapped density(gm/cm3) (Mean ± SD)

Hausner’s ratio

Carr’s index

F1 28.307±0.6150 0.530±0.0070 0.623±0.0082 1.175 14.923 F2 27.455±0.6111 0.547±0.0063 0.613±0.0072 1.121 10.767 F3 27.844±0.3108 0.560±0.0019 0.657±0.0036 1.120 14.764 F4 28.107±0.2877 0.524±0.0028 0.616±0.005 1.176 14.935 F5 28.307±0.6147 0.552±0.0026 0.619±0.003 1.121 10.824 F6 29.649±0.6573 0.549±0.0024 0.623±0.0045 1.135 11.879 F7 28.311±0.4192 0.549±0.0041 0.613±0.0045 1.117 10.440 F8 29.453±0.9582 0.524±0.0034 0.616±0.0032 1.176 14.935 F9 28.169±0.5296 0.499±0.0038 0.582±0.0064 1.166 14.261 F10 28.280±1.006 0.550±0.0026 0.618±0.00643 1.124 11.003 F11 27.791±0.4869 0.545±0.0119 0.616±0.0033 1.130 11.526 F12 30.159±0.7361 0.526±0.0049 0.620±0.0049 1.179 15.161

Averages of three were reported (n=3)

TABLE 8

Evaluation of isoniazid and rifampicin dispersible tablets

Formulation code

Uniformity of thickness(n=10)

(mm) (Mean ± SD)

Uniformity of diameter(n=10)

(mm) (Mean ± SD)

Hardness (n=10) (kg/cm2) (Mean ± SD)

% Friability (n=3) (Mean ± SD)

Uniformity of weight (n=20) (mg) (Mean ± SD)

F1 3.334±0.0143 11.043±0.0125 3.940±0.2367 0.122 ±0.0211 400.470 ± 1.0446 F2 3.337±0.0305 11.045±0.0071 3.760±0.3893 0.159 ±0.0332 400.648±1.5547 F3 3.364±0.0435 11.043±0.0094 3.820±0.1988 0.149 ±0.0224 400.0505±0.4906 F4 3.385±0.0598 11.045±0.0118 3.89±0.5259 0.145 ±0.0326 399.870±1.2394 F5 3.348±0.0539 11.044±0.0069 3.870±0.3653 0.142 ±0.0177 400.666±1.8367 F6 3.354±0.0327 11.052±0.0063 3.950±0.2549 0.134 ±0.0080 400.469±2.3334 F7 3.393±0.0782 11.051±0.0057 3.680±0.2251 0.163 ±0.0177 400.078±0.6532 F8 3.342±0.0247 11.049±0.0088 3.890±0.3218 0.189±0.0032 400.111±0.7499 F9 3.632±0.0779 11.058±0.0063 3.650±0.3100 0.165 ±0.0078 400.738±2.2067 F10 3.628±0.0528 11.061±0.0143 3.370±0.1159 0.153 ±0.0034 400.045±0.7117 F11 3.522±0.0636 11.056±0.0052 3.250±0.1080 0.156 ±0.0045 400.958±1.7456 F12 3.476±0.07367 11.061±0.0057 3.710±0.1449 0.189 ±0.0569 400.821±2.2955

TABLE 9

In-vitro dispersion and disintegration time and content uniformity of isoniazid and rifampicin dispersible tablets

Formulation codes

In vitro dispersion time (n=3)(sec) (Mean ± SD)

In vitro disintegration time (n=6)(sec)(Mean ± SD)

Content uniformity (%) (n = 3) (Mean ± SD) Isoniazid Rifampicin

F1 46.770±0.2836 30.010 ±0.1153 98.022±1.3936 99.744±0.2221 F2 37.187±0.1159 26.853 ±0.6058 98.621±0.0024 101.769±0.3846 F3 59.127±0.2267 40.997±0.4105 98.126±0.8678 98.333±0.5875 F4 45.153±0.1528 33.700 ±0.6426 98.736±0.7963 99.359±0.4441 F5 70.217±0.1250 49.543±0.6634 99.356±0.7178 98.205±0.4441 F6 58.330±0.2152 39.397±0.3317 98.506±0.1991 99.615±1.0176 F7 78.447±0.4924 51.590±0.4187 99.471±0.3982 98.0121±0.4443 F8 66.327±0.3842 44.103±0.5658 99.816±0.1991 98.589±0.5875 F9 24.400±0.3306 21.297±0.9404 100.195±0.3980 101.026±0.2221

F10 35.445±0.3787 23.897±0.7229 99.506±0.1789 100.256±0.4441 F11 47.710±0.2433 27.260±0.1735 99.081±0.5267 99.3589±1.5544 F12 58.563±0.4852 29.110±0.1998 98.046±0.1257 99.103±0.8882

Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2233  

In-vitro dissolution studies

The results obtained in the in vitro drug release for the formulations F1- F12 were tabulated in table 10-15.

The plots of cumulative % drug release vs. time were depicted in figure 4-9.

TABLE 10

Anti-tubercular activity of isoniazid, rifampicin, F2, F9 and marketed formulation

S.No. Samples Concentrations (µg/ml)

100 50 25 12.5 6.25 3.125 1.6 0.8

1 Isoniazid S S R R R R R R 2 Rifampicin S S S S S S S S 3 F2 S S S S S S S R 4 M S S S S S S S S 5 F9 S S S S S S S S

*R- Resistant *M-Marketed *S- Sensitive

TABLE 11

Selected formulations F2 and F9 for stability studies stored at 40 °C/75% RH

Formulation Code Tested After Time (in days)

Hardness (kg/cm2)

In-vitro Dispersion time (sec)

Friability % Mean ± SD

(n=3)

Drug content (%) Mean ± SD (n=3)

In-vitro % Drug release

Mean ± SD (n=3) Isoniazid Rifampicin Isoniazid Rifampicin

F2

Initial 3.760±0.3893 37.187±0.1159 0.159 ±0.0332 98.621±0.0024 101.769±0.3846 99.268 98.824

30 3.640±0.2871 35.682±0.1321 0.156±0.1332 98.492±0.1249 100.543±0.3369 98.0321 98.921

60 3.521±0.1991 35.114±0.1291 0.178±0.2671 98.012±0.1897 99.988±0.1096 98.111 97.128

90 3.021±0.0215 35.103±0.549 0.164±0.1136 98.001±0.0983 99.989±0.1187 98.001 97.032

Initial 3.650±0.3100 24.400±0.3306 0.165±0.0078 100.195±0.398 101.026±0.2221 99.029 98.181

F9 30 3.58±0.5498 24.054±0.2314 0.165±0.1178 99.023±0.7692 100.997±0.3219 98.874 98.095

60 3.434±0.1134 24.011±0.1310 0.169±0.451 98.993±0.5478 100.456±0.2314 98.983 98.941

90 3.401±0.0651 24.001±0.2012 0.164±0.1123 98.991±0.1143 100.412±0.7631 98.032 98.321

Fig. 4. Comparative In-vitro release profile of isoniazid for formulation F1-F8 in pbs pH 6.8 prepared by direct compression method.

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Fig. 5. Comparative In-vitro release profile of rifampicin for formulation F1-F8 in pbs pH 6.8 prepared by direct compression method.

Fig. 6. Comparative In-vitro release profile of isoniazid for formulation F9-F12 in pbs pH 6.8 prepared by sublimation method.

Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2235  

Fig. 7. Comparative In-vitro release profile of rifampicin for formulation F9-F12 in pbs pH 6.8 prepared by sublimation method.

Fig. 8. Comparative In-vitro release profile comparision of direct compression and sublimation for isoniazid.

2236 Int J Pharm Sci Nanotech Vol 6; Issue 4 • December 2013 (extra issue)  

Fig. 9. Comparative In vitro release profile comparision of direct compression and sublimation for rifampicin.

The dissolution rate was found to increase linearly with increase in the concentration of superdisintegrant where as when tablet formulated by sublimation method showed increase in vitro dissolution when compared with tablets formulated by direct compression.

Formulation F2 (4% w/w), which contained crospovidone formulated by direct compression, showed drug release of 99.268%, 98.824% for isoniazid and rifampicin respectively at the end of 20 min.

Formulation F9 (4% w/w), which contained crospovidone formulated by sublimation, showed drug release of 99.029 %, 98.188% for isoniazid and rifampicin respectively at the end of 14 min.

In all the formulations, the drug release was near to 100% and it was observed that drug release increased with increase in the concentration of superdisintegrant and order followed was crospovidone > pregelatinezed starch > croscarmellose sodium > sodium starch glycolate.

When compared with direct compression, formulations formulated by sublimation method showed faster dissolution i.e. within 14 minutes and 20 min respectively.

F9 formulation containing crospovidone (4%) prepared by sublimation method showed better and faster drug release compared to F2. This may be

attributed due to the mechanism of crospovidone which is rapid wicking by capillary action followed by swelling causing disintegration of the tablet and pore formation by removal of sublimating agent i.e. camphor.

Comparison of formulation with marketed product

In-vitro dissolution profiles of marketed product in comparison to the formulated batches were shown in Figure 10, 11. Formulation F2 with 99.268% and 98.824% (in 20 min.) and Formulation F9 with 99.029%, 98.181 % (14 min) of isoniazid and rifampicin drug release respectively. The marketed product showed 94.983% and 93.984% of isoniazid and rifampicin release at the end 20 min for in vitro dissolution study. Therefore F2 and F9 showed better drug release in comparison to marketed product.

Anti-tubercular activity

Remarkable anti-tubercular activity has been showed by the compound pure rifampicin which was effective against Mycobacterium tuberculosis H37 RV at all the tested dose levels. This is followed by the compound Pure isoniazid which was effective till 50 μg/ml. The formulations F2, F9 and marketed were found to be the next effective compounds in this study with MIC value of 1.6, 0.8 and 0.8 μg/ml respectively. Therefore it implies that isoniazid when combined with rifampicin shows better activity.

Bolmal et al: Comparative Evaluation of Isoniazid and Rifampicin Dispersible Tablets Prepared by Distinct Methods 2237  

Fig. 10. Comparative In vitro release profile of isoniazid for formulation F2, F9 and marketed in pbs pH 6.8.

Fig. 11. Comparative In vitro release profile of rifampicin for formulation F2, F9 and marketed in pbs pH 6.8.

2238 Int J Pharm Sci Nanotech Vol 6; Issue 4 • December 2013 (extra issue)  

Hence F9 formulation and marketed formulation were effective till 0.8 μg/ml. The anti-tubercular activity of the compounds revealed that the formulation F9 possess excellent activity in comparison with F2. Results are shown in table 10.

Stability Studies

The formulations (F2 and F9) did not show much variation in any of the parameters. The results obtained are tabulated in table 11. From these results it was concluded that, formulation F2, F9 were stable and retained its original properties.

Conclusions

In the current study a successful attempt was made to formulate different formulations (F1-F8) dispersible tablets of isoniazid and rifampicin by direct compression method using superdisintegrants (crospovidone, pregelatinized starch, croscarmellose sodium, sodium starch glycolate) separately and in different concentrations (2% and 4% w/w). The formulations containing 4% of superdisintegrants (F2, F4, F6, F8) prepared by direct compression method were selected as optimized and hence 4% of superdisintegrants were used for preparation of dispersible tablets by sublimation method (F9-F12). Disintegration time/Dispersion time decreased as the concentration of superdisintergrants increased from 2% w/w to 4% w/w. The relative efficiency of these superdisintegrants to improve the disintegration and dissolution rates of tablets was in the following order: crospovidone>pregelatinized starch> croscarmel-lose sodium> sodium starch glycolate. Among all, the formulation containing crospovidone (4% w/w) as superdisintegrant fulfilled all the parameters satisfactorily. Formulations (F9-F12) prepared by sublimation method showed better in vitro dispersion time and in vitro drug release (within 14 min.) in comparison to formulations (F2, F4, F6 and F8) prepared by direct compression method. The anti-tubercular activity of the compounds revealed that the compound F9 possess excellent activity in comparison with F2 and therefore it also implies that isoniazid when combined with rifampicin shows better activity. Formulation F9 showed faster drug release in comparison to the marketed formulation of isoniazid and rifampicin. Accelerated stability studies for best selected formulation F2 and F9 showed physicochemical stability for a period of 90 days at 40 °C±2ºC and 75% ±5% RH.

Acknowledgements

The authors acknowledge the support received from Themis Medicare Ltd., Haridwar (U.K.), India, for their support and encouragement in carrying out my work.

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Address correspondence to: Uday Bolmal, Assistant Professor, KLE University’s College of Pharmacy, Belgaum, Karnataka-10, India. Mob: +91-9945598377 ; E-mail: udaybolmal@yahoo.co.in