Formulation And Evaluation Of Er Tablet Biology Essay

The following drug and excipients were used for the formulation and evaluation of ER Tablet.







Anti –Retroviral drug



Polyox 303(PEO)

Rate controlling Polymer for sustained Release Tablet.

FMC Biopolymer


Povidone K-30,K-90


BASF Chemicals


Xanthan gum

viscosity-increasing agent

CP Kelco


Pharmatose –200M


Concord mart


Magnesium stearate





FMC Biopolymer

Kollidon SR



Sodium alginate

Rate controlling Polymer

FMC Biopolymer List of drug, excipients and uses

Table 12: List of Instruments used:





Analytical Balance

Sartorius BT224S


Dispensing Balance

Sartorius CPA8201


Tapped Density Tester

Electro lab ETD-1020


Electromagnetic Sieve Shaker

Electro lab EMS-8


Vibrator Sifter


GMP-LAB Sr no. 236


Octagonal and bin blender

Ganson GMP ,STD


Tablet compression machine 8 station

Kambet KMPC8

D- Tooling

B- Tooling


Digital vernier caliper



IR Moisture analyzer/Balance (LOD)

Sartorius MA150


Tablet hardness tester 8M

Dr.Schleuniger pharmatron 8M


Leak test apparatus

Sunson LT-101


Friabilator USP

Electro lab EF-2


Induction Cap Sealer

Electronic Device Mumbai.


Blister Packing machine

Precision George Ltd./ IMAPG Lab Model p.p.240 s.s.


Strip Packing Processor

Hemson Jayrons Automation System


pH meter



Dissolution Test apparatus



Fourier Transform Infrared Spectrophotometer (FT-IR)



Ultraviolet- visible Spectrophotometre

SHIMADZU UV-1700 Pharmaspec.


Vacuum Oven

Alpha Scientific IIMC


Ultrasonic bath

S.V. Scientific


Karl Fisher Apparatus



Preformulation may be described as a stage of development during which the physicochemical and biopharmaceutical properties of a drug substance are characterized. It is an important part of the drug development process. The information relating to drug development acquired during this phase is used for making critical decisions in subsequent stages of development. A wide variety of information must be generated to develop formulations rationally. Characterization of the drug is a very important step at the preformulation phase of product development followed by studying the properties of the excipients and their compatibility

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

The overall objective of Preformulation studies is to generate information useful to the formulator in developing stable and bioavailable dosage forms, which can be mass-produce.

Preformulation study can divided into two subclasses:


The compatibility of drug and formulation components is important prerequisite before formulation. It is therefore necessary to confirm that the drug does not react with the polymers and excipients under experimental conditions and affect the shelf life of product or any other unwanted effects on the formulation.


Active pharmaceutical ingredient (API) characterization

Organoleptic Evaluation:

These are preliminary characteristics of any substance, which is useful in identification of specific material. Following physical properties of API were studied






The solubility was determined using a method specified in the USP. The solubility profile of the investigational drug was important to determine a proper analytical method. There are two methods that are specified following the same dissolving procedures of the active substances.

Dissolving procedure

The substance is added to the solvent and shaken vigorously for 1 minute and placed in a constant temperature device. The temperature was maintained at 25±0.5ºC for 15 minutes. If the substance is not completely dissolved, the stirring or shaking is done for 1 minute and the solution is placed in the constant temperature device for period of another 15 minutes, and changes in solubility are observed under the two methods

Method 1:

For this test, a maximum of 1gram of substance for each solvent and solvent quantity of 30ml was taken necessarily.

Very soluble - 100mg of finely divided powdered substance in a stropper tube (16mm in internal diameter and 160mm long). 0.1ml of solvent is added and proceeded under dissolving procedure. The substance should be completely dissolved.

Freely Soluble – Further 9ml of solvent is added and proceeded under dissolving procedure for complete solubility.

Soluble – Further 2ml of solvent is added and proceeded as under dissolving procedure for complete solubility.

Sparingly soluble – Additional 7.0ml is added and proceeded under dissolving procedure for complete solubility

Slightly soluble – 10mg of finely powdered substance is taken in a stopper tube, and 10ml of solvent is added and proceeded under dissolving procedure for complete solubility.

Poorly/Very slightly soluble - 1mg of finely powdered substance in a stopper tube and 10ml of the solvent is added and proceeded under dissolving procedure. The substance should be completely soluble

Method 2:

For this test about 1 gm of substance is taken and dissolved in approximate volume of solvent in milliliters following dissolving procedures. The volume of solvent taken ranging from less than 1ml to 10,000ml or 10 liters specifies the solubility range of the active drug by given specifications in the table below.


Descriptive term

Approximate volume of solvent in milliliters per gram of solute

Very soluble

Less than 1ml

Freely soluble

From 1 to 10ml


From 10 to 30 ml

Sparingly soluble

From30 to 100ml

Slightly soluble

From 100 to 1000ml

Very slightly soluble

From 1000 to 10000ml

In the present study, method 1 was followed for obtaining clear variable ranges of solubility of the investigational drug.

The solvents selected for the investigational drug based on drug profile are: Phosphate buffer – pH 6.8.


Before any product development, it is very important to develop an appropriate analytical method that provides accuracy and precision which will be used throughout the development process for the determination of assay and in-vitro dissolution process.

Preparation of Stock solution:

50mg of the drug was accurately weighed and transferred into the 100 ml volumetric flask. It was dissolved in sufficient quantity phusphate buffer ph 6.8 +6% SLS and volume was made up to the mark with buffer to get a 100 µg/ml solution. This was the stock solution containing 500 µg/ml of model drug.(Stock 1).

Preparation of Standard solution:

Withdraw 1 ml solution from the stock solution and transferred into 100ml volumetric flask it was dissolved by using ph 6.8 phosphate buffer+6% SLS. And the volume was made up to the mark with ph 6.8 phosphate buffer to get 5 µg/ml solution . This was the standard solution containing 5 µg/ml of model drug .

Preparation of the calibration curve:

From the standard solution, take the solution 0.2, 0.5 ,0.7 ,0.1, 1.2 and 1.5 ml This solution was then scanned in a wavelength range of 200 to 400 nm using a UV Spectrophotometer. Before measuing of absorbance the spectrum of standard solution was measured it was found to be wavelength 232 nm.Absorbance of each solution was measured at 232 nm. The Standard curve preparation was performed in triplicate. The absorbances were plotted against the concentrations and the graph with the straight line equation and r2 value were obtained. This solution was then scanned in a wavelength range of 200 to 400 nm using a UV Spectrophotometer.


Infrared Spectroscopy

The IR absorption spectra of the pure drug and with different excipients were taken in the range of 4000-450 cm-1 using KBr disc method, 1-2 mg of the substance to be examined was triturated with 300-400 mg, specified quantity, of finely powered and dried potassium bromide .These quantities are usually sufficient to give a disc of 10-15mm diameter and pellet of suitable intensity by a hydraulic press.

API and excipients were thoroughly mixed in predetermined ratio given in table 20. and through the sieve no.40. The blend was filled in glass vials and closed with gray rubber stoppers and sealed with aluminum seal and charged in to stress condition at 25ºC/60%RH and 40ºC/75%RH. Similarly API was also kept at all conditions as per the sample. The samples were observed for any physical change in 1 week,2 week,3 and 4 week duration . The Infrared spectrum of model drug was recorded by using FT-IR spectroscopy and observed for characteristic peaks of drug.

Table 14 : Drug excipient compatibility study protocol

Sl. No.

Name of the substance




Model Drug (API)



API + Kollidone SR



API+Xanthan gum



API + Aerosil






API + povidone K90



API+ povidone K25



API + Sodium alginate



API + Magnesium stearate




Extented release tablets containing 400 mg of model drug were prepared with a total tablet weight of 1000mg. Considering the preformulation studies and the literature survey conducted the excipients were selected and an attempt to produce ER tablets .

Selection of polymers :

Long duration of action with good release is the most important characteristics of XR tablets. The necessity of a extended release tablet is to long acting in stomach . polymers Kollidone SR, Sodium aginate and ,PVP- K90,Xanthan gum,PEO used in the concentration range of 6 to 10 % to prepare initial trial batches and a study was carried out.

Selection of diluents

Since direct compression method and wet granulation method were followed the choice of directly compressible diluent was direct compressible,dicalcium phosphate and pharmatose 200M used respectively. Microcrystalline cellulose was selected as the filler or diluent owing to its multiple functionality as binder, disintegrant, compressibility and flowability.

Selection of other ingredients

Magnesium stearate (1%) as lubricant were incorporated, also magnesium stearate decreases the hardness of tablets without affecting the release time*.

. Povidone K-25 was used in the concentration of 1.5-7.5% as binder.


The main aim of the present study was to formulate different batches using binders and polymers in varying concentrations .So different batches of formulations was planned accordingly. According to that trials was formulated .The model drug used was among the Biguanide antihyperglycemic agent groups.

METHOD OF FORMULATION: Direct compression method :

Model drug + binder

Then Pass through sieve(sieve no.40)

Add Diluent , Then Pass through sieve(sieve no.40)

Collect the powder mixture;

Subject the blend for tablet formulation ( Direct compression)


Drug and binders were weighed and mix with binders. The dry drug and binder mixture were mixed with the excipients and passed through sieve no:40 except and lubricant .Weighed amount of drug binder mixture and exicipient were mixed in geometric dilution method. The blend was further lubricated with Magnesium stearate (preseived through sieve no:60) and the powder blend is subjected to drying and was compressed by direct compression method by using Standard concave punches in 8 Station Kambet KMPC8 tablet punching machine and punches measuring 19.5mm and 9mm diameter were used for compression. Tablet of 748mg and 753mg was prepared in different trials by adjusting hardness and volume screw of compression machine properly.

Wet granulation method:

Model drug + polymer(binder)

Then Pass through sieve(sieve no.40)

Add Diluent , half part of binder

Then Pass through sieve(sieve no.40)

DM water

Prepare granules ,and dry wet mass up to 1.5 to 2.50 moisture maintain ofter add remaining part of binder then mix 5 minutes, lubricated with

Magnesium stearate (pre-sifted through sieve no. 60) mix 5 minutes

Subject the blend for tablet formulation (compression)


Weighed quantity of Drug and polymer as per formula transferred in a stainless steel container. Added sufficient quantity of Demineralised water in to it. Weighed amount of excipients were mixed with API . Prepared the granules after passing sieve no.#10 and dried granules in a Rapid Dryer till the LOD Came between 1.5-2.5%. Passed the granules by sieve no.#20. mixed the remaing quantity of excipients and lubricated the blend with magnesium stearate and was compressed by wet granulation method by using Standard concave and with break line punches in 8 Station Kambert KMPC8 tablet punching machine. Standard concave punches measuring 19.5mm, with breakline punches measuring the Tablet of 1000mg,1020mg,1010mg and 1030mg was prepared in different trials by adjusting hardness and volume screw of compression machine properly.


Angle of Repose (USP29-NF-24);

The angle of repose has been used to characterize the flow properties of solids. Angle of repose is a characteristic related to interparticulate friction or resistance to movement between particles. This is the maximum angle possible between surface of pile of powder or granules and the horizontal plane. was calculated using the following equation

tan = h / r

 = tan –1 h / r

Where, h = height of the powder heap

r = radius of the powder heap

θ = angle of repose

The results were reported as Mean ± SD values

The angle of repose of granules was determined by the fixed funnel and free standing cone method. The accurately weighed granules were taken in a funnel .A funnel was fixed at a height approximately of 2-4 cm over the platform. The loose powder or granules were allowed to flow through the funnel freely onto the surface, till the cone of the powder formed.

Angle of Repose

S. No.

Angle of repose

Flow property













Determination of Bulk Density and Tapped Density: (USP29-NF-24)

Bulk density:

Bulk density of a compound varies substantially with the method of crystallisation, milling or formulation. It is of great importance when one considers the size of a high – dose capsule product or the homogeneity of a low dose formulation in which there are large differences in drug and excipient densities. In addition to bulk density, it is frequently desirable to know the true density of a powder for computation of void volume or porosity of packed powder beds.

An accurately weighed quantity of the granules/ powder (W) was carefully poured into the graduated cylinder and volume (V0) was measured. Then the graduated cylinder was closed with lid and set into the tap density tester (USP). The density apparatus was set for 500 taps after 750 taps and the volume (Vf) was measured and continued operation till the two consecutive readings were equal. The bulk density and the tapped density were calculated using the following formulae.

Bulk density = Weight of powder(g) / Bulk volume(ml)

Tapped density:-

Tapped densities the drug was determined by pouring gently 25 gm of sample through a glass funnel into a 100 ml graduated cylinder. The cylinder was tapped from height of 2 inches until a constant volume was obtained. In USP TAP DENSITY TESTER, Tap density is measured in 500taps, 750 taps & 1250taps with drop/time-299-302.

The tapped density was measured for 500 tappings and 750 tappings giving densities (Va), and (Vb) with a drop time of 299 to 302 tappings per minute.

If the percentage difference between the ‘Va‘ and ‘Vb’ exceed about 2% than ‘Vc’ is measured by 1250 tappings. Either ‘Vb’ or ‘Vc’ is taken as the final tapped density. The volume occupied by the sample after tappings were recorded and the tapped density was the formula below

Tapped density = Weight of powder(g) / Tapped volume(ml)

Tap Density tester

Carr’s compressibility index:-

Compressibility is the ability of powder to decrease in volume under pressure. Compressibility is a measure that is obtained from density determinations. It is also one of the simple methods to evaluate flow property of powder by comparing the bulk density and tapped density. The percentage compressibility of a powder was a direct measure of the potential powder arch or bridge strength and stability.

High density powders tend to possess free flowing properties. A useful empirical guide is given by the Carr’s index or compressibility index calculated from bulk density and tapped density. Carr’s index of each formulation was calculated according to equation given below

Tapped density – Bulk density

carr’s index = X 100

Tapped density

Flow properties corresponding to compressibility index as per USP31- NF26

% Compressibility

Flow  description












Very poor


Extremely poor

Hsausner’s ratio: -

Hausner’s ratio provides an indication of the degree of densification which could result from vibration of the feed hopper. A lower value of indicates better flow and vice versa. Hausner’s Ratio indicates the flow properties of the powder and is measured by the ratio of tapped density to bulk density. It is the ratio of tapped density and bulk density.Hausner found that this ratio was related to interparticle friction and, as such, could be used to predict powder flow properties. Generally a value less than 1.25 indicates good flow properties, which is equivalent to 20% of Carr’s index.

Hausner’s Ratio = Tapped density /Bulk density

Specifications of Hausner’s ratio



Less than 1.25

Good  Flow (20% Carr’s index)

1.25 – 1.5

Moderate (33% Carr’s index)

(adding glidant normally improves flow)

Greater than 1.5

Poor  Flow

(Glidant has marginal effect)

Particle size distribution:-

Size, shape & surface morphology of drug particles affects the flow, formulation homogeneity, dissolution & chemical reactivity of drugs Particle size of drugs may affect formulation and product efficacy. Certain physical and chemical properties of drug substances are affected by the particle size distribution including: drug dissolution rate, bioavailability, content uniformity, taste, texture, color, stability, flow characteristics, and sedimentation rates. Particle size also has effect on the drug’s absorption.

Satisfactory content uniformity in solid dosage forms depends to a large degree on particle size and the equal distribution of the active ingredient throughout the formulation.

Particle size distribution was carried out in "Elecromagnetic Sieve Shaker"

(Electrolab EMS-8

Sieve analysis method:

The particle size distribution was carried out by using electromagnetic sieve shaker.Placed 10gm of the drug sample on the top (coarest) sieve, and magnetic vibration was created for 5 minutes. Then carefully removed each from the nest without loss of material. The percentage of retention was recorded.

Loss on Drying (LOD)

The loss on drying (%) is measured by using Infrared Moisture analyzer-Sartorius MA 150. About 1gm of the blend is taken and kept for drying at a temperature range of 105º C for a period of 5 minutes with a standard heating of 60º C. The Loss on Drying is automatically displayed by the analyzer in percentage values. The loss on drying for every formulation was carried out thrice and reported as Mean ± SD values.

Melting point determination: Melting point of model drug was determined by open capillary method. The capillary tube was closed at one end by fusion and was filled with drug by repeated tappings. The capillary tube was placed in digital melting point apparatus.the instrument was set to automatically increase the temperature of heating bath at a rate of one degree celcious min rise of temperature per minute.The rise in temperature was viewed through magnifying lens.the temperature at which the drug started melting was recorded .this was performed thrice and the average value was calculated.

Evaluation of Tablets

I .Pre-Compression Parameters:

Angle of repose

Bulk density

Tapped density

Compressibility index

Hausner’s ratio

Particle size distribution (Sieve analysis.)

Loss on Drying. (Dry mix and final blend)

These parameters are determined using the same procedure as described previously in preformulation study.

II. Post- compression parameters:

The quantitative evaluation and assessment of a tablet‘s chemical, physical and bioavailability properties are important in the design of tablets and to monitor product quality. These properties are important since chemical breakdown or interactions between tablet components may alter the physical tablet properties, and greatly affect the bioavailability of the tablet system. There are various standards that have been set in the various pharmacopoeias regarding the quality of pharmaceutical tablets. These include the diameter, size, shape, thickness, weight, hardness, disintegration and dissolution characters. The diameters and shape depends on the die and punches selected for the compression of tablets. The remaining specifications assure that tablets do not vary from one production lot to another. The following standards or quality control tests should be carried out on compressed tablets.

General appearance:-

The general appearance of tablets, its visual identity and overall ‘elegance’ is essential for consumer acceptance, control of lot-to-lot uniformity and general tablet-to-tablet uniformity and for monitoring the production process. The control of general appearance involves measurement of attributes such as a tablet’s size, shape, color, presence or absence of odor, taste, surface textures, physical flaws and consistency.

Size and shape:-

The type of tooling determines the shape and dimensions of compressed tablets during the compression process. At a constant compressive load, tablets thickness varies with changes in die fill, particle size distribution and packing of the powder mix being compressed and with tablet weight, while with a constant die fill, thickness varies with variation in compressive load. Tablet thickness is consistent from batch to batch or within a batch only if the tablet granulation or powder blend is adequately consistent in particle size and particle size distribution, if the punch tooling is of consistent length, and if the tablet press is clean and in good working condition.

Uniformity of Thickness:-

The thickness of individual tablets may be measured with a micrometer, which permits accurate measurements and provides information of the variation between tablets. It can be measured by Vernier calliper. Tablet thickness should be controlled within a ± 5% variation of a standard value. Any variation in thickness within a particular lot of tablets or between manufacturer’s lots should not be apparent to the unaided eye for consumer acceptance of the product. In addition, thickness must be controlled to facilitate packaging.

Hardness or crushing strength:-

The resistance of tablets to capping, abrasion or breakage under conditions of storage, transportation and handling before usage depends on its hardness. It is now designated as either the Monsanto or Stokes hardness tester. The instrument measures the force required to break the tablet when the force generated by a coil spring is applied diametrally to the tablet.

Hardness, which is now more appropriately called crushing strength determinations are made during tablet production and are used to determine the need for pressure adjustment on tablet machine. The force required to break the tablet is measured in kilograms and a crushing strength of 4Kg is usually considered to be the minimum for satisfactory. Oral tablets normally have a hardness of 4 to 10kg; however, hypodermic and chewable tablets are usually much softer (3 kg) and some sustained release tablets are much harder (10-20 kg). For floating tablet (3.5-4.5kg) The most widely used apparatus to measure tablet hardness Dr.Schleuniger apparatus.

Friability test:

It was done in Roche friabilator apparatus where the tablets were subjected to the combined effect of abrasion and shock by utilizing a plastic chamber that revolve at 25 rpm dropping the tablets at a distance of six inches with each revolution. . Friability is expressed in percentage (%). Preweighed samples of 20 tablets were placed in the friabilator, which is then operated for 100 revolutions. The tablets were then dusted and reweighed. Conventional compressed tablets that loss than less than 1.0% of their weight are generally considered acceptable.

% Friability of tablets less than 1% is considered acceptable. Thus, it is necessary that this parameter should be evaluated and the results are within bound limits (0.1-0.9%).

Friability Tester

Uniformity of weight:-

Weigh individually 20 units taken at random or, for single-dose preparations presented in individual containers, the contents of 20 units, and determine the average mass. Not more than 2 of the individual masses deviate from the average mass by more than the percentage deviation and none deviates by more than twice that percentage

Weight Variation Test:

The weight variation test of the tablets was done as per the guidelines of Indian Pharmacopoeia. Ten tablets from each batch were weighed in digital balance and average weight was determined and standard deviation was calculated. The USP has provided limits for the average weight of uncoated compressed tablets. These are applicable when the tablet contains 50mg or more of the drug substance or when the latter comprises 50% or more, by weight of the dosage form.

Twenty tablets are weighed individually and the average weight is calculated. The individual tablet weights are then compared to the average weight. Not more than two of the tablets must differ from the average weight by not more than the percentages stated in following tablet must differ by more than double the relevant percentage.

The following percentage deviation in weight variation is allowed according to USP:

Standard percentage deviation in weight

Average Weight of a tablet

Percentage deviation

130mg or less


More than 130mg through 324mg


More than 324mg


In all the formulations the tablet weight was more than130mg and less than 324 mg, hence 7.5% maximum difference allowed.

Drug Content Uniformity

The drug content is determined for obtaining the amount and percentage of drug retained in the dosage unit of particular tablet lot. It is done by assay on application of suitable analytical procedure that is developed initially meant to give the stated amount of percentage of active drug that the dosage unit comprises. The percentage of drug content should comply with the specification of stated amounts in the individual monographs in the pharmacopoeias by any suitable analytical procedure.

The investigational drug that belongs to the anti diabetic class chas been reported in the monographs to have ‘Not less than 90% and not more than 110% of stated amount of the drug’.

Preparation of standard solution:

50mg of investigational drug was accurately weighed and dissolved in 100ml of methanol in a volumetric flask and considered as ‘stock’. From the stock about 1 ml is taken in a volumetric flask and made up to 100ml to give solution with concentration of 5 µg/ml.

Preparation of sample solution:

About 10 tablets were weighed and the average weight is taken. The tablets were powdered in a mortar and pestle and the weight equivalent to 100mg of investigational drug was taken and transferred into a volumetric flask. The volume was made with 100ml methanol on vigorous shaking, and this is considered as a ‘stock’.

The stock is filtered using whatmann filterpaper of 45µm and 1 ml of filtrate is than diluted to 100ml using phosphate buffer ph 6.8 to get 5µg/ml concentration. The absorbance of the resulting solution was measured at 232nm by UV spectrophotometer which is obtained by development of analytical procedure.

The calculations and the amount by assay and percentage of drug content present in the formulation are determined by the equations given below

Assay calculation: The amount of drug present was calculated by given formula,

A1 Std. Wt 1 mL 100 mL 100 mL P 100 mL Assay = --------- × ----------- × ------- × ­­­­­­­­­­­ ­­­­­­­­--------- × ------ × ------ × -------× Avg.wt

Amount (mg) A2 100mL 100 mL Sam.wt. 1 mL 100 mL LC


A1 - Sample Absorbance

A2 - Standard Absorbance

P - Potency of drug

LC - Label Claim

Percentage of drug content (%) =

In Vitro Dissolution Studies:

Dissolution is the process by which a solid solute enters a solution. In the pharmaceutical industries, it may be defined as the amount of drug substance that goes into the solution per unit time under standard condition of liquid/solid interface, temperature and solvent composition.

Dissolution is consider as a on of the most important quality control test performed on the pharmaceutical dosage forms and is now developing into tool for predicting bioavailability, and in some case, replacing clinical studies to determine bioequvalance. dissolution behaviour has significant effect on their pharmacological activity. In fact, a direct relationship between in-vitro dissolution rate of many drugs and their in-vivo bioavailability has been demonstrated and is generally referred to as in-vitro to as in-vivo-in-vitro correlation, IVIVC.

The development of in-vitro dissolution methods is comparable to approaches taken for other extended release oral dosage forms., the dissolution is carried USP type II (paddle) apparatus.

The monographs of the investigational drug specified in the USP states the use dissolution media such as pH 6.8 .

Dissolution testing condition:


The most commonly used dissolution test methods are

Basket method

Paddle method

The basket and paddle method are simple, robust, well standardized and used worldwide. These methods are flexible enough to allow dissolution testing for variety of drug product.. Dissolution methods and apparatus described in the USP are generally used either with manual sampling or with automated procedure.

Dissolution medium:

Dissolution testing should be carried out under the physiological condition, if possible. This allows interpretation of data in regards to in-vivo performance of the product. The testing condition should be based on physicochemical characteristics of drug substance and environmental condition.

The volumes of the dissolution medium generally 1000mL.. An aqueous medium with pH range 6.8 should be used.

Method: The development of in-vitro dissolution methods for extended release Tablet Commonly the drugs may have dissolution conditions as in USP monograph. Media such as pH 6.8 phosphate buffer used for evaluation of XR tablet Experience has indicated that USP 2 paddle apparatus is most suitable and common choice for dissolution test of Extended release tablets, where a paddle speed of 100 rpm is commonly used. Typically the dissolution of ER Tablet is very long when using USP monograph conditions. Hence slower paddles speeds may be utilized to obtain a comparative profile.

Dissolution of the tablet of each batch was carried out using USP type II (paddle) apparatus dissolution type II apparatus (LABINDIA DISSO 2000). As per the official recommendation of USFDA. 1000ml of pH 6.8 phosphate buffer used as dissolution medium and the temperature of the medium was set at 37 ± 0.5 0C. 5ml of sample was withdrawn at predetermined time interval of 1, 2, 3, 6, and 10 same volume of fresh medium was replaced. The withdrawn samples were analyzed by an UV spectrophotometer at 232 nm The drug content was calculated using the equation generated from standard calibration curve. The % cumulative drug release was calculated.

Percentage Drug Release (%) =

T.A std.wt. 5 mL dissolution volume 1 potency

× × × × × × 100

S.A 100 mL 100mL lable claim 1 100mL

Where: T.A = Test absorbance; S.A = Standard absorbance;

Summary of general dissolution conditions

Sl. No.




Dissolution medium

Ph 6.8 phosphate buffer+6% SLS





Rotation speed

50 rpm





Volume withdrawn

10 ml



275 nm


The drug release kinetics are studies by the use of various mathematical models. The mathematical models by means of graphical method that best fits the drug release profile data of a particular drug is chosen based on coefficient of Linea regression (R2) value.

The model that gives the high ‘R’ value is considered as the best fit model of drug release for the respective release profile data. In order to determine the drug release kinetics, by graphical method, mathematical parameters such as Cumulative % drug release, log of Cumulative % drug release, log of time, root of time are in turn calculated from the graph. The various mathematical models for release kinetics are that are being applied for the current formulation are:

Zero order release model.

First order release model.

Zero-order release system with rapid release component.

First order release system with rapid release component.

Higuchi release model.

All the models of release kinetics mentioned above are fitted to the drug release profile of the optimized formulation through the use of graphical method in determining coefficient of linear regression (R2) value. The Linear Regression (R2)values are processed from the data of mathematical models using the MS EXCEL statistical function software.

Zero order release system

This model applies to drugs if they are stable in fluids at the absorption site, similar absorption efficiency from all the absorption sites and is absorbed rapidly and completely. In this model the rate of drug appearance in plasma is equal to rate of release from controlled release dosage form.

The time to reach study state concentration depends upon half-life (t1/2). Slower the elimination, more time to reach the study state concentration

Graphical method – A graph is plotted with the time taken on X-axis and cumulative % drug release was taken on Y-axis, a straight line should be obtained.

Slow first order release systems

They are inferior to zero – order release systems, in this system smaller and smaller amounts of drug are released as the time passes.

Graphical method –A graph is plotted with time taken X-axis and log cumulative % dug release taken on y-axis. Curved line is obtained.

First order release system with rapid release component

In this system, the drug reaches fast release initially, than slowly releases the drug with increase in time.

Graphical method – A graph is plotted with time taken on X-axis followed by the % drug release on y-axis. the graph gives elevation initially followed by minimal decline and subsequent elevation.

Higuchi Model The model suggests drug release by Ficki’s first law of diffusion. this model tells various diffusion paths like Fickian diffusion, anomalous diffusion or non-anomalous diffusion and case 2 relaxation or Super core transport. It is given by equation

Q = Kt1/2

where: Q = Cumulative amount of drug release at time ‘t, k = higuchi constant, and t = time in hours

Graphical model – a graph is plotted on square root of time taken on X-axis and cumulative % of drug release on Y-axis. It gives a straight line.

Korsmeyer – Peppas Release model.

This model is applicable to logarithmic determination of drug release kinetics, when fitted to any drug release profiles, which are based on mainly drug diffusion release. Systems. It is given by the equation:

F = Mt /m = km* t n

Where: F = Fraction of drug released at time‘t’; Mt = amount of drug released at time‘t’; m = total amount of drug in the dosage form; km = kinetic constant; n = diffusion or release exponent. T = time in hours.

Graphical Method – A graph is plotted using ‘log of time’ on X-axis and log cumulative % drug release on y-axis. It gives a straight line intercepting the X-axis.

The Linear Regression (R2) values of various release kinetic models fitted to the optimized formulation are obtained by processing the data using Microsoft EXCEL statistical function.

Stability Studies

Stability of a drug has been defined as the ability of a particular formulation, in a specific container, to remain within its physical, chemical, therapeutic and toxicological specifications.

The purpose of stability testing is to provide evidence on how the quality of a drug substance or drug product varies with time under the influence of a variety of environmental factors such as temperature, humidity an light and enables recommended storage conditions, re-test periods and shelf lives to be established.

Generally, the observation of the rate at which the product degrades under normal room temperature requires a long time. To avoid the undesirable delay, the principles of accelerated stability studies are adopted.

The international conference on harmonization (ICH) guidelines titled "stability of new drug substances and products" (QIA) describes the stability test requirements for drug registration application in the European Union, Japan, and United States of America

ICH specifies the length of study and storage conditions:

Long term testing 25C ± 2C / 60 % RH ± 5 % for 12 months

Intermediate testing 30ºC ± 2ºC / 70% RH for 6 months

Accelerated testing 40C ±2 C / 75 % RH ± 5 % for 3 months

In the present study, stability studies were carried out at 40oC ± 2oC / 75% RH for a period of one month following every week from the initial week. The tablets of the optimized trail were prepared and stored in High density Polyethylene (HDPE) containers and evaluated every week for the changes in Weight variation, hardness, friability, The parameters were carried out 3 times per every interval of study.