Preparation and Characterization of Bi-Layer Matrix Tablets of Amoxicillin Tri-Hydrate

P Narayana Raju^*1, M Lakshmi Narasu², KNV Rao³, K Shanta Kumari³ and K Prakash⁴

¹Aurobindo pharma limited, Research and development, Bachupally, Hyderabad, AP, India.

²Centre For Biotechnology, Institute of Science and Technology, JNTU, Kukatpally, Hyderabad, AP, India

³Nalanda College of Pharmacy, Charlapally, Nalgonda, AP, India

⁴Faculty of Pharmacy, 7th April University, Zawia, Libya

*Corresponding Author E-mail: nrpadala@rediffmail.com

ABSTRACT

Amoxicillin bi layer matrix tablets were prepared using cellulose acetate (CA) and cellulose acetate butyrate (CAB) as matrix polymers for the extended release of amoxicillin. The matrix tablets consists of one immediate release layer which release the drug immediately and one sustained release layer which release the drug for a prolonged period of time. The matrix tablets were prepared by direct compression method. The prepared matrix tablets were characterized for the physical properties, drug content, differential scanning calorimetry (DSC) and in vitro dissolution studies. The prepared matrix tablets were kept for accelerated stability study as per ICH guidelines for about 3 months. The prepared bi layer matrix tablets were showing good physical properties. The initial rapid drug release from the bi layer matrix tablets was observed. The drug release was extended up to 16 hours. Differential scanning calorimetric thermographs shows the stable nature  of Amoxicillin tri-hydrate. The release kinetics study revealed that the prepared bi-layer matrix tablets were best fitted to the first order. All the formulations were best fitted to Higuchi model indicated that the drug release was diffusion controlled. The prepared matrix tablets were having high commercial application.

KEYWORDS: Amoxicillin tri-hydrate; cellulose polymers; bi layer matrix tablets; controlled release; stability.

INTRODUCTION:

Amoxicillin trihydrate is a widely prescribed broad-spectrum antibiotic, available in conventional dosage forms. The conventional formulations such as capsules, tablets, suspensions produce a large plasma peak of drug about 2 h after administration, which rapidly declines to below the minimum inhibitory concentration (MIC) of most pathogenic microorganisms, before the administration of subsequent doses of 250-500 mg at 8 h intervals¹. It has often been claimed without clinical substantiation that this pulsed pattern of administration is more effective than sustained delivery of therapeutic concentration of active, as it may encourage outgrowth of resistant organisms when antibiotic levels become sub-therapeutic². However, this suggestion is at variance with practice of giving the antibiotic as its sodium salt by slow intravenous infusion when treating severe infections and by the increasing use of orally active cephalosporin and tetracycline antibiotics with once- or twice-a-day dosage regimen.

Also, it has been shown in vitro that β -lactam antibiotics differ from aminoglycosides in that their antibacterial effect was less concentration dependent, but was more related to the duration of active antibiotic level³.

Attempts to develop a sustained release dosage form of amoxicillin have been hindered by its dose size, short biological half-life of 1-2 h, high sensitivity to light, moisture and heat.

Cellulose polymers are commonly known for their use in taste masking formulations and sustained release tablets^4-8. Before 1960’s, tablet manufacturing often required wet granulation process to convert the active ingredients in to flowable and compressible powder⁹. However some limitations such as segregation and content uniformity were reported¹⁰.

In the present study we have prepared bi layer tablets of amoxicillin trihydrate. One layer releases the drug immediately and the second layer release the drug for a prolonged period of time. Two cellulose polymers such as cellulose acetate (CA) and cellulose acetate butyrate (CAB) were used for the prolonged drug release.

Table 1 Formulation components of immediate release and extended release granules of amoxicillin tri-hydrate

Formulation	FI	FX-1	FX-2	FX-3	FX-4	FX-5	FX-6
Components	Immediate release layer	Extended release layer
	mg per tablet
Amoxicillin	100	150	150	150	150	150	150
Cellulose acetate (CA)		20	30	40	--	--	--
Cellulose acetate Butyrate (CAB)		--	--	--	20	30	40
Lactose (Pharmatose DCL 21)	30	--	--	--	--	--	--
Micro crystalline cellulose (PH200)	45	40	30	20	40	30	20
Sodium starch glycolate (SSG)	10	--	--	--	--	--	--
Aerosil	6	6	6	6	6	6	6
Talc	4	4	4	4	4	4	4
Magnesium stearate	5	5	5	5	5	5	5
Granules weight	200	225	225	225	225	225	225
Immediate release granules	--	200	200	200	200	200	200
Tablet weight		425	425	425	425	425	425

Table 2 Physical and chemical properties of immediate release and extended release formulations of amoxicillin tri-hydrate

Formulation		F-1	F-2	F-3	F-4	F-5	F-6
	Immediate release layer	Extended release layer
Physical Properties
Granules
Drug content (% )	99.3	99.26	99.33	99.57	99.82	100.02	99.96
Bulk density (BD)  (g/ml)	0.56	0.59	0.53	0.57	0.61	0.51	0.53
Tapped density (TD) (g/ml)	0.71	0.76	0.7	0.73	0.79	0.69	0.72
Compressibility index (CI)	21.12	22.36	24.28	21.91	22.78	26.08	26.38
Tablets
Weight variation (mg)		425 ±5	423 ±2	424 ±5	427 ±3	425 ±3	424 ±5
Hardness (kg/cm^2)		9.6±2	8.7±2	9.3±1	9.1±2	9.6±3	8.7±2
Thickness (mm)		4.2 ±0.2	4.1±0.2	4.2±0.3	4.2±0.1	4.1±0.1	4.2±0.2
Friability (%)		≤0.5	≤0.5	≤0.5	≤0.5	≤0.5	≤0.5
Disintegration time (Seconds)	35±5	-	-	-	-	-	-
Release kinetics
Zero order (r^2)		0.7477	0.7588	0.7525	0.7734	0.7831	0.7498
First order (r^2)		0.9406	0.9048	0.9452	0.9245	0.9075	0.9670
Higuchi release (r^2)		0.9075	0.9306	0.9687	0.9411	0.9481	0.9576

MATERIALS AND METHODS:

Materials:

Amoxicillin tri hydrate was obtained as a gift sample from Tini Pharma, Renugunta, Tirupati, India. Cellulose acetate (CA) (CA 398 10-NF) and cellulose acetate butyrate (CAB) (CAB-171-15 PG) was obtained from Eastman chemical company, USA. All other chemicals and reagents used in the study were of analytical grade.

Methods:

Preparation of immediate release granules:

Immediate release granules were prepared by direct blending of amoxicillin with lactose (Pharmatose DCL 21), microcrystalline cellulose (Avicel PH-200) and sodium starch glycolate. The dry mix blend was then pre lubricated with aerosol and talc. The pre lubricated blend then lubricated with magnesium stearate. The lubricated granules were characterized for BD, TD, CI and drug content.

Preparation of extended release granules:

Extended release granules of Amoxicillin were prepared using various proportions of CA and CAB as the retarding polymer. The granules were prepared by the direct blending of the drug, polymer(s) and all other excipients are mixed uniformly. The dry mix blend was then pre lubricated with aerosol and talc. The pre lubricated blend then lubricated with magnesium stearate. The lubricated granules were characterized for BD, TD, CI and drug content.

Preparation of bi- layer matrix tablets:

The quantity of granules for the immediate release granules were placed in the die cavity and compressed at low compression pressure using a single punch-tableting machine (Cadmach Machinery Co Pvt. Ltd., India) equipped with 11.5 mm round, flat and plain punches. Over this compressed layer, the required quantity of the extended release granules were placed and compressed to obtain hardness in the range of 10 kg cm–2 to form a bi layer matrix tablet. The matrix tablets prepared with CA were coded as FX-1, FX-2, FX-3 and the matrix tablets prepared with CAB were coded as FX-4, FX-5, FX-6. The formula and physical characteristics of the prepared matrix tablets are given in Table 1 and 2.

CHARACTERIZATION OF BI-LAYER MATRIX TABLETS:

Drug content determination:

The drug content was determined by developed UV spectrophotometric method¹¹. Ten tablets were finely powdered and an amount equivalent to 250 mg of amoxicillin trihydrate was accurately weighed and transferred to a 100 mL volumetric flask, then 70 mL of citrophosphate buffer was added. The flask was shaken for 10 min. Finally, the volume was made up to the mark with water. The mixture was then filtered and 1 mL of the filtrate was suitably diluted with water to obtain a solution containing about 25 μg mL^–1 of amoxicillin tri-hydrate and the absorbance was measured at 272 nm using Shimadzu UV 1608 spectrophotometer.

Fig 1: Percentage drug release of Amoxicillin from different formulations (□) 8% cellulose acetate, (▲) 13.5% cellulose acetate, (♦) 18% cellulose acetate, (■) 8% cellulose acetate butyrate, (●) 13.5% cellulose acetate butyrate, (○) 18 % cellulose acetate butyrate,

In vitro dissolution studies:

In vitro dissolution studies were performed using USP type II dissolution apparatus (LABINDIA, DISSO-2000, Mumbai, India) at 100 rpm. USP dissolution tester type II was used. Tablets as well as granules were evaluated in the dissolution medium pH 6.8 phosphate buffer (900 ml, 37^OC, n=3) for 16 hours. The samples were withdrawn at predetermined time intervals and the absorbance was measured at 272 nm using Shimadzu UV 1608 spectrophotometer.

Kinetic analysis of dissolution data:

The rate and mechanism of release of amoxicillin from the prepared bi layer tablets were analyzed by fitting the dissolution data into the zero-order equation

Q = k₀t

Where, Q is the amount of drug released at time t, and k₀ is the release rate constant,  The dissolution data was fitted to the first order equation

ln (100–Q) = ln 100 – k₁t.

Where, k1 is the release rate constant. The dissolution data was fitted to the Higuchi’s equation

Q = k₂ t ^1/2

Determination of stability of the bi layer matrix tablets:

The optimized formulation from in vitro dissolution data were selected and filled in the HDPE containers and stored at the following condition like 40°C/75 RH for about 3 months as per ICH guidelines. The samples were characterized for % drug content and DSC study.

Differential scanning calorimetry (DSC) study:

Differential scanning calorimetry (DSC) study of bi layered matrix tablets was performed using a Diamond DSC (Mettler Star SW 8.10) to determine the drug excepient compatibility study. The analysis was performed at a rate 5 ⁰ C min ^-1 from 50⁰ C to 200⁰ C temperature range under nitrogen flow of 25 ml min ^-1.

Fig 2: In-vitro dissolution showing the amoxicillin release from immediate release layer during first hour (A) Matrix tablets of cellulose acetate (B) matrix tablets of Cellulose acetate butyrate.

RESULTS:

Bi-layer matrix tablets of amoxicillin were prepared, the flow properties of the both immediate release and extended release granules showed excellent flow. Good compressibility index of 21.12 % was observed in immediate release layer. Compressibility index range of 21.91 to 26.38 % was observed in the extended release layers. Table 2 describes the physical characteristics of prepared bi layer tablets. Disintegration time of immediate release layer was found to be around 35 sec. Hardness of the prepared bi layer matrix tablets was found in the range of 8.7 to 9.6 kg/cm². Very low friability was observed in all the formulation.

The release of drug from all the formulations is from 10 hrs to 16 hrs and more (Figure-1). Initial burst effect was observed and 41- 49 % drug released (Fig-1) in the first hour in all the formulations showing the rapid disintegration of immediate release layer form the bi layer matrix tablets (Figure-2). Figure 2 describing the rapid drug release from the immediate release layer form both the matrix tablets. The drug release from extended release mainly depends on the concentration and type of polymer used in the preparation of formulations. Slow release rate was observed with cellulose acetate butyrate than cellulose acetate. The release mechanism of amoxicillin form various formulations was determined by comparing their respective correlation coefficients (Table-2). The drug release form all formulations was first order followed by zero order. All the formulation best fitted to Higuchi model indicated that the drug release was diffusion controlled.

The interaction study between the drug and polymer from the prepared formulations was evaluated using differential scanning calorimetry (DSC) study.  DSC thermo gram of pure amoxicillin showed a sharp endothermic peak at 149.6°C (Fig-3). The thermo grams of formulations, FX-1 and FX-4 also showed the same endothermic peak at the similar temperature. This confirmed that there is no drug to polymer interaction. The assay results of all the formulations were found good. The assay results of accelerated stability study on the prepared bi layered showed good correlation between initial and stability samples. This further confirmed the stable nature of amoxicillin in the prepared bi layer matrix tablets.

DISCUSSION:

Amoxicillin bi layer matrix tablets were prepared and evaluated with reported method. The granules of matrix tablets were shows good compressibility index. The hardness indicates the good mechanical strength of the tablets.  The immediate release layer released approximately 50% of the drug in the first hour and extended the remaining drug for about 16 hours. It was clearly observed that as the polymer proportion increases the drug release rate decreases in both polymers. The drug release retarded more in the formulation containing cellulose acetate butyrate than cellulose acetate phthalate.  The formulations follow first order release. The Higuchi model of all formulations indicated that the formulations follow diffusion model. The release was mainly depends on the type of polymer and viscosity.  Release of drug was slow with matrix tablets of prepared with cellulose acetate butyrate than cellulose acetate. The DSC study indicated that there is no drug polymer interaction. The results of accelerated stability study revealed the stable nature of the drug.

CONCLUSION:

Results of the present study demonstrated that the prepared bi layer tablets were showing immediate and extended release profiles of the amoxicillin and prolonging the drug release up to 16 hours. This can be expected to reduce the frequency of administration and decrease the dose-dependent side effects associated with repeated administration of conventional amoxicillin tablets. The in-vitro dissolution of tablets showed that the drug release was mainly depends on the type of polymer and viscosity of the polymer. The DSC study of the present study clearly indicated that there is no drug and polymer interaction. The accelerated stability of the prepared matrix tablets showed stable nature of Amoxicillin tri hydrate. 

Fig 3: DSC thermo grams of (A) Pure amoxicillin (B) amoxicillin matrix tablets with CAP (C) amoxicillin matrix tablets with CAB, (D) 3 months stability sample of amoxicillin matrix tablets with CAP and (E) 3 months stability sample of amoxicillin matrix tablets with CAB

ACKNOWLEDGEMENTS:

The authors are greatly acknowledging the Tini Pharma,  Renugunta, Tirupati, India, for supply of amoxicillin tri-hydrate as gift sample. The authors are grateful to Indian Institute of chemical technology, Hyderabad, India for help in performing the characterization studies.

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Received on 21.02.2009       Modified on 12.04.2009

Accepted on 28.06.2009      © RJPT All right reserved

Research J. Pharm. and Tech.2 (3): July-Sept. 2009,;Page 491-494