Formulation and In Vitro Assessment of Controlled Release Matrix Tablets of Abacavir

D. Varun , B.V.P. Deepthi*, P.V. Ayodhya Neelima, G. Suma Latha, M. Srikar, B. Anuhya and V. Siva Lalitha

Hindu College of Pharmacy, Amaravathi Road, Guntur, Andhra Pradesh, India.

ABSTRACT:

The main objective of the present work was to develop controlled release matrix tablets of abacavir using different polymers namely hydroxy propyl methyl cellulose (HPMC), polyethylene oxide, pharmatose DCL 21, microcrystalline cellulose. Varying ratios of drug and polymer were selected for the study. The tablets were prepared by direct compression and wet granulation method. After evaluation of physical properties of tablet like hardness, friability, thickness, weight variation, the in vitro release study was performed by using USP type 1 dissolution apparatus in pH 6.8 phosphate buffer for 14 h. The effect of polymer concentration and polymer blend concentration were also studied. Release kinetics of abacavir matrix tablets were done by zero order, first order, higuchian square root studies. The matrix tablets prepared with combination of HPMC K 100 M and PEO, showed slower release pattern when compared the matrix tablets prepared with HPMC K 100 M alone is clear indication of the drug release over a prolonged period. The DSC and FTIR study revealed that there was no chemical interaction between drug and excipients.

KEYWORDS: Abacavir, HPMC, polyox, pharmatose, aerosil, controlled release.

INTRODUCTION:

Human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome (AIDS), commonly referred to as HIV/AIDS, constitute one of the most serious infectious disease challenges to public health globally^1. Abacavir (as sulfate), a nucleoside and nucleotide reverse transcriptase inhibitors active against Human Immunodeficiency Virus Type 1 (HIV-1) in a dosage of 300 mg tablets is indicated for the treatment of HIV infection in combination with other antiretroviral agents^2. Oral drug delivery systems have progressed from immediate release to site specific delivery over a period of time³. Abacavir is a carbocyclic synthetic nucleoside analogue used for the treatment of HIV/AIDS. Intracellularly, Abacavir is converted by cellular enzymes to the active metabolite carbovir triphosphate, an analogue of deoxyguanosine-5'-triphosphate (dGTP). Carbovir triphosphate inhibits the activity of HIV-1 reverse transcriptase (RT) both by competing with the natural substrate dGTP and by its incorporation into viral DNA. Abacavir is rapidly and extensively absorbed after oral administration having bioavailability of 83%. The elimination half-life of a drug is about 1.54 ± 0.63 h and the usual oral dosage regimen is 300 mg twice daily⁴. To reduce the frequency of administration and to improve patient compliance, a sustained release formulation of Abacavir is developed⁵. The main objective of the present work was to develop sustained release matrix tablets of Abacavir using different polymers viz. Hydroxy propyl methyl cellulose (HPMC), polyethylene oxide, pharmatose DCL 21, microcrystalline cellulose etc. Varying ratios of drug and polymer were selected for the study.

After fixing the ratio of drug and polymer for control the release of drug up to desired time, the release rates were modulated by combination of two different rate controlling materials. The matrix tablets were prepared and evaluated for different physicochemical parameters such as appearance, weight variation, thickness, hardness, friability, drug content and in vitro release. The marketed product was evaluated for the said physicochemical parameters and the in vitro release of Abacavir from the developed formulation was compared with the marketed one.

MATERIALS AND METHODS:

Abacavir was procured as a gift sample obtained from Sashan Pharmaceutical Pvt. Ltd, Coimbatore. HPMC K 100 M was purchased from Colorcon Asia Private Ltd, India. Polyox WSR 303 was purchased from DOW chemical company, USA. Pharmatose DCL21 was purchased from DMV International, Netherlands. Avicel PH 200 was purchased from FMC Biopolymers, USA. Aerosil was purchased from Degussa, Germany. Talc was purchased from Luzenac, France. 0.45 µ (Millipore) filter was obtained from Millipore, USA. Magnesium stearate was purchased from Ferro Industrial Chemicals USA. Starch 1500 was purchased from Colorcon Asia Private Ltd, India. Di-sodium hydrogen Phosphate was purchased from Rankem , India. All other solvents and reagents were of analytical grade.

Methods:

Formulation of matrix tablets :

Matrix tablets of Abacavir were prepared using various proportions of HPMC and combination of HPMC and PEO as the retarding polymer .The tablets were manufactured by direct compression procedure. The lubricated granules were directly compressed using 9mm flat faced round (FFR) punch. Three batches were prepared for each formulation and compressed 500 tablets from each batch for the characterization study. The formulae and physical characterstics of the prepared matrix tablets were shown in table-1.

Preparation of matrix tablets using direct compression method:

The drug, polymer(s) and all other excipients sifted through 425 m sieve(ASTM mesh no 40) and mixed uniformly. The dry mix blend was then pre lubricated with respective excipients and lubricated with magnesium stearate. The lubricated granules were directly compressed on 16 station tablet compression machine using respective punches (Cadmach Machinery Co, Ahmedabad, India).

Preparation of matrix tablets using wet granulation method:

The drug, polymer and other excipients were sifted through 425 m sieve(ASTM mesh no 40) and mixed uniformly. The dry mix blend was then granulated with respective granulation fluid. The wet granules were dried at 60⁰c until the complete evaporation of granulation fluid from the granules. The dried granules were again sifted through ASTM mesh no 30.The dried and sifted granules were then pre lubricated with respective excipients and then lubricated with magnesium stearate. The lubricated granules were compressed on 10 station tablet compression machine using respective punches (Cadmach Machinery Co, Ahmedabad, India).

Evaluation of tablets :

The prepared tablets were evaluated for weight variation, hardness, thickness, friability, drug content, and in vitro release studies. Tablet hardness was determined for 10 tablets using a Monsanto hardness tester (MHT-20, Campbell Electronics, Mumbai, India. The tablet to be tested is placed between the spindle and anvil and pressure applied by turning the screw knob just to hold the tablet in position .The reading of the indicator on the scale is adjusted to zero. The pressure is applied until the tablet breaks. The reading was noted^[6]. In this work, for each formulation the hardness of 6 tablets was evaluated.

The weight variation was determined by taking 20 tablets using an electronic balance (type ER182A, Mettler Toledo). In weight variation test twenty tablets were selected at a random and average weight was calculated. Then individual tablets were weighed and the weight was compared with an average weight.

Friability was determined by testing 10 tablets in a friability tester (FTA-20 Campbell Electronics) for 300 revolutions at 25 rpm. This device subjects the tablets to the combined effect of abrasions and shock in a plastic chamber revolving at 25 rpm and dropping the tablets at a height of 6 inches in each revolution. Preweighed sample of tablets was placed in the friabilator and were subjected to 100 revolutions. Tablets were dedusted using a soft muslin cloth and reweighed. The friability (F) is given by the formula:

F = (1- W₀ / W) × 100

Where, W₀ is the weight of the tablets before the test and W is the weight of the tablet after the test. For the determination of drug content, the prepared matrix tablets were divided in triplicate. For each batch, 20 tablets were taken, weighed and finely powdered. An accurately weighed quantity of this powder was taken and suitably dissolved under sonication (power sonic 505, HWASHIN technology Co) in pH 6.8 phosphate buffer and filtered through 0.45 m (Milli pore) filters. The samples were analyzed by UV visible spectro photometer at 285nm after making appropriate dilutions The in vitro dissolution studies were performed upto 14 h using USP type-2 dissolution apparatus (paddle type, LABINDIA,DISSO -2000, Mumbai, India)at 100 rpm. The dissolution medium consisted of phosphate buffer pH 6.8(900ml), maintained at 37⁰c. An aliquot (5ml) was withdrawn at specific time intervals and filtered through 0.45 m (Millipore ) filter. After appropriate dilutions, the samples were analyzed by UV visible spectro photometer at 285nm and cumulative percentage of the drug release was calculated. The mean of 6 tablets from 3 different batches was used in data analysis.

Fourier transform infrared radiation measurement (FT-IR):

The FT-IR spectrums of pure drug, initial formulation and stability samples of matrix tablets were determined. A FT-IR (Thermo nicolet 670 spectrometer) was used for the analysis in the frequency range between 4400 cm^-1 and 4 cm^-1 resolution. The results were the means of 6 determinations. A quantity equivalent to 2 mg of pure drug was used for the study.

Differential scanning calorimetry(DSC) study:

Thermal properties of pure drug, initial formulation and stability samples of matrix tablets were evaluated by differencial scanning calorimetry (DSC) using Diamond DSC (Mettler Star SW 8.10).The analysis was performed at a rate 5⁰c min^-1 from 50⁰c to 200⁰c temperature range under nitrogen flow of 25 ml min^-1.

RESULTS AND DISCUSSION:

Matrix tablets of Abacavir were compressed with 9 mm flat faced round punch. The tablets were examined for various physical properties. No sticking was observed during the compression process. It clearly indicates that the uniform lubrication of the blend. Good flow was observed with the use of the directly compressible excipients. The tablets were physically evaluated for hardness, friability. A hardness range of 7.5-8 kg/cm² was observed. No friability was observed which indicates the mechanical strength of the tablets. No capping tendency was observed upon physical examination of the tablets during compression and hardness testing. The formulae and physical characterstics of the prepared matrix tablets were shown in table no -1.

Table no.1 Formulation and physical characterstics of designed controlled release matrix tablets of Abacavir

FORMULATION COMPONENTS	F-1	F-2	F-3	F-4	F-5	F-6
	mg per tablet
Abacavir	200	200	200	200	200	200
HPMC K 100 M	35	25	15	65	50	35
Poly ethylene oxide	10	10	10	--	--	--
Pharmatose DCL 21	20	25	30	10	15	20
Micro crystalline cellulose (AVICEL PH 200)	20	25	30	10	20	30
Aerosil	6	6	6	6	6	6
Talc	4	4	4	4	4	4
Magnesium stearate	5	5	5	5	5	5
Physical/ chemical Properties
Drug content (% )	99.815	100.85	100.5	99.86	99.5	100.3
Hardness (kg/cm2)	7.5 ±0.3	7±0.4	7 ±0.4	7.1 ±0.3	7.2 ±0.3	8 ±0.1
Thickness (mm)	3.60	3.55	3.61	3.53	3.6	3.57
Friability (%)	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1

The matrix tablets prepared with combination of HPMC K 100 M and PEO have shown slower drug release rates when compared to those prepared with HPMC K 100 M. The formulation F-1 released 74% if the drug in 12 h . It was clearly observed that as the concentration of HPMC K 100 M decreased the release rate was increased (F-2 and F-3) as shown in Table-2.

The in vitro dissolution of designed controlled release matrix tablets of Abacavir were shown in table-2. The comparative release profiles of Abacavir from controlled release matrix tablets were shown in fig. 1.

Similarly, the tablets prepared with HPMC K 100 M also shown drug release of 80-100% in about 10 h. It was observed that, as concentration of the HPMC K 100 M increased the drug release rate was decreased. The initial release for the first hour varied between 5-11% for the matrix tablets prepared with combination of HPMC and PEO. The initial release for the matrix tablets prepared with HPMC K 100 M alone was found to 7-17%. This variation in the release at initial hour is mainly because of the polymer proportion and type of polymer used in the preparation of the matrix tablets, but the release was more controlled in the later stage in the tablets prepared with higher proportion of the polymer. The release was extended and increased up to 10 h and more. Good correlation was observed in zero order plots (0.984-0.997)(Table-3), indicating that the drug release was independent of the concentration. The release kinetics were best fitted to the higuchi model kinetics, indicates the drug release mechanism was predominantly diffusion controlled. Increase in release rate constant for 29.17 to 33.14(Table-3), indicates the drug release was dependent on the proportion of the polymer (F-1, F-2 and F-3). Similar pattern was observed in the matrix tablets prepared with HPMC K 100 M. (F-4, F-5, and F-6). The time to release 50% of drug is found to be 6.96-8.16 h in matrix tablets prepared with combination of HPMC and PEO and 5.39-7.94 h for those prepared with HPMC alone is clear indication of the drug release over a prolonged period.

Table no.2 In vitro dissolution of designed controlled release matrix tablets of Abacavir(n=3)

Time	F-1	F-2	F-3	F-4	F-5	F-6
0	0	0	0	0	0	0
1	10(±2.2)	16(±3.1)	21(±2.1)	18(±3.1)	22(±2.1)	27(±3.1)
2	16(±3.6)	22(±1.6)	34(±1.7)	26(±2.2)	31(±3.7)	41(±4.1)
3	31(±1.6)	39(±1.7)	58(±1.5)	39(±3.7)	43(±2.1)	69(±2.2)
6	47(±1.9)	57(±2.9)	69(±2.7)	52(±4.2)	61(±2.1)	82(±2.1)
8	59(±2.6)	71(±2.3)	86(±3.2)	67(±3.1)	72(±3.2)	100(±2.3)
10	74(±1.3)	86(±3.2)	92(±2.2)	81(±3.2)	89(±2.1)	--
12	83(±2.2)	94(±1.6)	100(±2.1)	90(±1.1)	100(±1.1)	--

Table no.3 . Release kinetics of Abacavir matrix tablets

Formulation	Zero order			First order			Higuch square root
	r2	t1/2	K	r2	t1/2	K	r2	t1/2	K
F-1	0.997	8.16	6.1	0.941	5.82	0.12	0.908	2.93	29.17
F-2	0.997	7.35	6.8	0.905	3.82	0.18	0.931	2.36	32.53
F-3	0.984	6.96	7.2	0.945	3.62	0.19	0.969	2.27	33.14
F-4	0.994	7.94	6.3	0.925	4.71	0.15	0.941	2.82	29.74
F-5	0.991	7.34	6.8	0.908	4.38	0.16	0.948	2.46	31.84
F-6	0.989	5.39	9.3	0.967	3.46	0.2	0.958	1.74	37.83

Fig. 1 Comparative release profile of abacavir from controlled release matrix tablets prepared using different proportions of HPMC K 100M and combination of HPMC K 100M and PEO. Data point represents the average of 6 tablets from 3 batches with SD

Screening of the formulation :

Based on the in vitro dissolution studies, two formulations, i.e.,F-2 and F-5 were selected for the further studies.

To study the effect of lubricant on the compression parameters, the concentration of the magnesium stearate was decreased. A 0.5% and 1% magnesium stearate was incorporated in the formulation. The tablets with 0.5% magnesium stearate was showing slight sticking of the tablets to the punch. In case of 1% magnesium stearate there was no sticking was observed. Based on the lubricant study, the 1% magnesium stearate was optimized and selected in final formulation and in vitro dissolution study was conducted on the final formulation. The final formulation was given in table-4 and in vitro dissolution data conducted on final formulation was given in table-5.

Fourier transform infrared radiation measurement (FT-IR):

The FT-IR spectrum was taken for Abacavir powder. The characteristic peak of the carbonyl group (present in cytidine nucleus) at 1632.56 cm^-1 ; a band of peaks at 3267.36 and 3186.81 cm^-1 owing to amino and hydroxyl groups; and peaks at 1196.18 and 1086.57 cm^-1 owing to asymmetrical and symmetrical stretching of the C-O-C system (present in the oxathiolane ring). This further confirmed the pure Abacavir and also the stable nature of the drug in the formulation. The FTIR spectra was shown in figure-2.

Table no.4 Optimized formulation of Abacavir matrix tablets

Formulation Components	F-7	F-8
	mg/ tablet	mg/ tablet
Abacavir	200	200
HPMC K 100 M	25	--
HPMC K 100 M	--	50
Poly ethylene oxide	10	--
Pharmatose DCL 21	25	15
Micro crystalline cellulose (AVICEL PH 200)	27	22
Aerosil	6	6
Talc	4	4
Magnesiumstearate	3	3
Total in mg	300	300

Table no.5 Dissolution of optimized Abacavir matrix tablets(n=3)

Time (hr)	F-7	F-8
2	18 (± 2.3)	23(± 1.8)
6	40(± 1.6)	41(± 2.6)
8	59(± 3.3)	63(± 1.4)
10	73(± 2.7)	70(± 2.2)
12	86(± 1.1)	87(± 2.1)

Similarly FT-IR spectra of the accelerated stability samples were acquired at 1 and 3 mo. Similar bands were observed for carbonyl group at 1650.99(1 mo) and 1651.35(3 mo). Band peaks of 1285.33,1158.89 at (1mo) and 1285.58, 1158.58 at (3 mo) owing to asymmetrical and symmetrical stretching of the C-O-C system present in the oxathiolane ring. Band peaks at 3208.26 and 3213.43 confirm the hydroxyl group at 1 and 3 mo respectively. Band peaks at 3328.03 and 3330.77 confirm the amine group at 1 and 3 mo respectively.

Fig. 2 FTIR overlay spectra of 1.Pure Abacavir, 2.matrix tablets with HPMC K 100M and PEO

Differential scanning calorimetry(DSC) study:

DSC thermogram of pure Abacavir showed a sharp endothermic peak at 180^oc .The thermograms of formulations also showed the same endothermic peak at the similar temperature, confirming that there is no drug to polymer interaction in the formulations at initial time . The DSC thermograms were shown in figure-3.

Similarly DSC study of 3 mo accelerated stability samples(40^oc/ 75% RH)showed the similar sharp endothermic peak at 180^oc further confirming the stable nature of the drug in the formulations.

Fig . 3 . DSC thermograms of 1.Pure Abacavir 2.Abacavir matrix tablets.

SUMMARY AND CONCLUSION:

The use of cellulose ether polymers in oral controlled release dosage forms, such as matrix tablets was investigated. Hydroxypropyl methylcellulose (HPMC) and Polyethylene oxide (PEO) polymers were used to formulate and control the release of active ingredients from the hydrophilic matrix tablet formulations. The processing parameters were developed and optimized in order to achieve desired rate of drug release from the prepared drug delivery system. DSC results demonstrated a sharp endothermic peak for Abacavir at 179-180°C, which corresponded to its melting point. FTIR results demonstrated the characteristic peaks confirms the pure Abacavir. Physical properties of the prepared granules for matrix tablets results good flow properties. The matrix tablets of Abacavir were compressed with 9 mm flat faced round punch. Influence of polymer concentration and combination of polymers was investigated with HPMC and combination of HPMC and PEO. The matrix tablets prepared with combination of HPMC K 100 M and PEO, showed slower release when compared the matrix tablets prepared with HPMC K 100 M alone. Variation in the polymer concentration yielded different drug release patterns. Effect of combination of polymer also influenced the drug release. Variation in drug release at initial hour was observed in the formulations. The release was extended up to 14 h and more. Good correlation was observed in zero order plots with a correlation coefficient of 0.984-0.997. The release kinetics were best fitted to the Higuchi model kinetics, indicated the drug release mechanism was diffusion controlled. Elimination half-life was found to be 6.96 - 8.16 h in matrix tablets prepared with combination of HPMC and PEO and 5.39-7.96 for matrix tablets prepared with HPMC alone is clearly indicated the drug release for prolonged period. Magnesium stearate concentration was optimized and 1 % magnesium stearate yielded good results with respect to physical properties. DSC and FTIR studies demonstrated that there is no drug-polymer interaction . In conclusion, very promising in vitro results were observed with matrix formulations of Abacavir, further there is a scope to conduct the bioavailability studies in human volunteers to know the exact pharmacokinetic parameters

ACKNOWLEDGEMENTS:

The authors are thankful to Management of Hindu College of Pharmacy, Guntur for providing necessary facility for the work.

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Received on 21.10.2011

Accepted on 28.10.2011

© A&V Publication all right reserved

Research Journal of Pharmaceutical Dosage Forms and Technology. 3(6): Nov.- Dec., 2011, 298-303