PREFORMULATION STUDIES(TIZANIDINE)

PREFORMULATION STUDIES

PHYSICAL AND ORGANOLEPTIC PROPERTIES OF TIZANIDINE

PROPERTIES	SPECIFICATIONS
Colour	White to off-white
Appearance	fine crystalline powder
Odour	Odourless or faint characteristics odour

ASSAY OF RAW MATERIAL OF TIZANIDINE MUCOADHESIVE TABLET

PROCEDURE

Solution A: 6.8 mg/mL of monobasic potassium phosphate. Adjust with 5.3N potassium hydroxide to a pH of 7.5 ± 0.05.

Mobile phase: Acetonitrile and Solution A (20:80)

System suitability solution: 46 mg/mL of USP Tizanidine Hydrochloride RS and 0.12 mg/mL of USP Tizanidine Related

Compound C RS in Mobile phase

Standard solution: 0.046 mg/mL of USP Tizanidine Hydrochloride RS in Mobile phase

Sample solution: 0.046 mg/mL of Tizanidine Hydrochloride in Mobile phase.

Chromatographic system:

(See Chromatography (621), System Suitability.)

Mode: LC

Detector: UV 230 nm

Column: 4.6-mm ´ 15-cm; packing L7

Column temperature: 35°

Flow rate: 1 mL/min

Injection size: 20 mL

System suitability

Sample: Standard solution

[NOTE—The relative retention times for tizanidine related compound C and tizanidine are 0.5 and 1.0, respectively.]

Suitability requirements

Resolution: NLT 13.0 between tizanidine and tizanidine related compound C

Tailing factor: NMT 1.6 for tizanidine

Relative standard deviation: NMT 2.0%

Analysis

Samples: Standard solution and Sample solution Calculate the percentage of C9H8ClN5S · HCl in the portion of Tizanidine Hydrochloride taken:

Result = (rU/rS) ´ (CS/CU) ´ 100

rU = peak response of tizanidine from the Sample solution.

rS= peak response of tizanidine from the Standard solution

CS = concentration of USP Tizanidine Hydrochloride RS in the Standard solution (mg/mL)

CU = concentration of the Sample solution (mg/mL)

Acceptance criteria: 98.0%–102.0% (8)

DETERMINATION OF BULK DENSITY OF RAW MATERIAL

Bulk density is defines as weight per unit volume of material.Bulk density is determined by measuring the volume of a known mass of powder sample that has been passed through a screen into a graduated cylinder (Method I) or through a volume-measuring apparatus into a cup (Method II).

Method—Measurement in a Graduated Cylinder

Procedure

·         Unless otherwise specified, pass a quantity of material sufficient to complete the test through a 1.00-mm (No. 18) screen to break up agglomerates that may have formed during storage. Into a dry 250-mL cylinder introduce, without compacting, approximately 100 g of test sample, M, weighed with 0.1% accuracy.

·         If it is not possible to use 100 g, the amount of the test sample and the volume of the cylinder may be modified and the test conditions specified with the results. Select a sample mass having an untapped apparent volume of 150 to 250 mL. A 100-mL cylinder is used for apparent volumes between 50 mL and 100 mL. Carefully level the powder without compacting, if necessary, and read the unsettled apparent volume, V_o, to the nearest graduated unit.

·         Calculate the bulk density, in g per mL, by the formula:

(M) / (V_o)

Observations and Calculations of xanthan gum as polymer:

                             Mass of sample = 100g

                            Volume of sample in cylinder = 210ml

                                   Bulk density = M/V_o

                                                  = 100/210

                                                  = 0.476g/ml

Result:

       Bulk density of xanthan gum is 0.476g/ml

       Bulk density of tizanidine HCl is 0.488 g/ml

DETERMINATION OF TAPPED DENSITY OF RAW MATERIAL

Tapped density is achieved by mechanically tapping a measuring cylinder containing a powder sample. After observing the initial volume, the cylinder is mechanically tapped, and volume readings are taken until little further volume change is observed. The mechanical tapping is achieved by raising the cylinder and allowing it to drop under its own weight a specified distance by either of two methods. Devices that rotate the cylinder during tapping may be preferred to minimize any possible separation of the mass during tapping down.

Method

Procedure

·         Proceed as described above for the determination of the bulk volume (V0). Secure the cylinder in the holder.

·         Carry out 10, 500, and 1250 taps on the same powder sample and read the corresponding volumes V10,V500, and V1250 to the nearest graduated unit.

·         If the difference between V500 and V1250 is less than nor equal to 2 mL, V1250 is the tapped volume. If the difference between V500 and V1250 exceeds 2 mL, repeat in increments such as 1250 taps, until the difference between succeeding measurements is less than nor equal to 2 mL.

·         Fewer taps may be appropriate for some powders, when validated. Calculate the tapped density (g/mL) using the formula:

M/VF

   

              In which VF is the final tapped volume.

Observations and Calculations of xanthan gum as polymer:

                             Mass of sample = 46.5

                             Initial volume before tapping = 100ml

                                   Volume after tapping = 75ml                                             

                                 Tapped density = M/Vf

                                                                 = 46.5/75

                                                      = 0.62g/ml

Result:

        Tapped density of xanthan gum is 0.62g/ml

        Tapped density of Tizanidine HCl is 0.58g/ml (13)

DETERMINATION OF FLOW PROPERTIES

Determination of flow properties include angle of repose, compressibility index and Hausner ratio.

1)      ANGLE OF REPOSE:

The angle of repose has been used in several branches of science to characterize the flow properties of solids. Angle of repose is a characteristic related to inter particulate friction or resistance to movement between particles. Angle of repose test results is reported to be very dependent upon the method used. Experimental difficulties arise as a result of segregation of material and consolidation or aeration of the powder as the cone is formed. Despite its difficulties, the method continues to be used in the pharmaceutical industry, and a number of examples demonstrating its value in predicting manufacturing problems appear in the literature.

“The angle of repose is the constant, three-dimensional angle (relative to the horizontal base) assumed by a cone-like pile of material formed by any of several different methods (described briefly below).”

Basic Methods for Angle of Repose

A variety of angle of repose test methods are described in the literature. The most common methods for determining the static angle of repose can be classified on the basis of the following two important experimental variables:

1. The height of the “funnel” through which the powder passes may be fixed relative to the base, or the height may be varied as the pile forms.
2. The base upon which the pile forms may be of fixed diameter or the diameter of the powder cone may be allowed to vary as the pile forms.

Variations in Angle of Repose Methods

In addition to the above methods, the following variations have been used to some extent in the pharmaceutical literature:

• Drained angle of repose is determined by allowing an excess quantity of material positioned above a fixed diameter base to “drain” from the container. Formation of a cone of powder on the fixed diameter base allows determination of the drained angle of repose.

Angle of Repose General Scale of Flowability

Although there is some variation in the qualitative description of powder flow using the angle of repose, much of the pharmaceutical literature appears to be consistent with the classification by Carr, which is shown in table. There are examples in the literature of formulations with an angle of repose in the range of 40 to 50 that were manufactured satisfactorily. When the angle of repose exceeds 50, the flow is rarely acceptable for manufacturing purposes.

Table: Flow Properties and Corresponding 
Angles of Repose

Flow Property	Angle of Repose (degrees)
Excellent	25–30
Good	31–35
Fair—aid not needed	36–40
Passable—may hang up	41–45
Poor—must agitate, vibrate	46–55
Very poor	56–65
Very, very poor	>66

Experimental Considerations for Angle of Repose

Angle of repose is not an intrinsic property of the powder; i.e., it is very much dependent upon the method used to form the cone of powder. The following important considerations are raised in the existing literature:

• The peak of the cone of powder can be distorted by the impact of powder from above. By carefully building the powder cone, the distortion caused by impact can be minimized.
• The nature of the base upon which the powder cone is formed influences the angle of repose. It is recommended that the powder cone be formed on a “common base,” which can be achieved by forming the cone of powder on a layer of powder. This can be done by using a base of fixed diameter with a protruding outer edge to retain a layer of powder upon which the cone is formed.

Recommended Procedure for Angle of Repose

·         Form the angle of repose on a fixed base with a retaining lip to retain a layer of powder on the base.

·         The base should be free of vibration.

·         Vary the height of the funnel to carefully build up a symmetrical cone of powder.

·         Care should be taken to prevent vibration as the funnel is moved.

·         The funnel height should be maintained approximately 2–4 cm from the top of the powder pile as it is being formed in order to minimize the impact of falling powder on the tip of the cone.

·         Determine the angle of repose by measuring the height of the cone of powder and calculating the angle of repose,, from the following equation:

tan (α) = height/ 0.5 base

Observations and Calculations of xanthan gum as polymer:

             Height of heap = 5cm

             Radius (0.5 base) = 4cm

             tan (α) = height/ 0.5 base

                tan (α) = 5/4

                tan (α) = 1.25

                       α   = tan^-11.25

                            = 51.34⁰

Result:

Ø  Angle of repose of xanthan gum is 51.34⁰. According to specification sample is poorly flow and must require agitation and vibration for flow.

Ø  Angle of repose of tizanidine HCl is 29.33⁰. According to specification drug has Excellent flowability.

Flow Property	Angle of Repose (degrees)
Excellent	25–30
Good	31–35
Fair—aid not needed	36–40
Passable—may hang up	41–45
Poor—must agitate, vibrate	46–55
Very poor	56–65
Very, very poor	>66

2) COMPRESSIBILITY INDEX AND HAUSNER RATIO

In recent years the compressibility index and the closely related Hausner ratio have become the simple, fast, and popular methods of predicting powder flow characteristics. The compressibility index has been proposed as an indirect measure of bulk density, size and shape, surface area, moisture content, and cohesiveness of materials because all of these can influence the observed compressibility index. The compressibility index and the Hausner ratio are determined by measuring both the bulk volume and the tapped volume of a powder.

Basic Methods for Compressibility Index and Hausner Ratio:

Although there are some variations in the method of determining the compressibility index and Hausner ratio, the basic procedure is to measure (1) the unsettled apparent volume, V_O, and (2) the final tapped volume, V_f, of the powder after tapping the material until no further volume changes occur. The compressibility index and the Hausner ratio are calculated as follows:

Alternatively, the compressibility index and Hausner ratio may be calculated using measured values for bulk density (_bulk) and tapped density (_tapped) as follows:

In a variation of these methods, the rate of consolidation is sometimes measured rather than, or in addition to, the change in volume that occurs on tapping. For the compressibility index and the Hausner ratio, the generally accepted scale of flowability is given in Table^*,

Compressibility Index (%)	Flow Character	Hausner 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

Experimental Considerations for the Compressibility Index and Hausner Ratio:

Compressibility index and Hausner ratio are not intrinsic properties of the powder; i.e., they depend on the methodology used. In the existing literature, there are discussions of the following important considerations affecting the determination of (1) the unsettled apparent volume, V_o, (2) the final tapped volume, V_f, (3) the bulk density, _bulk, and (4) the tapped density, _tapped :

·    The diameter of the cylinder used

·    The number of times the powder is tapped to achieve the tapped density

·    The mass of material used in the test

·    Rotation of the sample during tapping

Recommended Procedure for Compressibility Index and Hausner Ratio

·         Use a 250-mL volumetric cylinder with a test sample weight of 100 g. 

·         Smaller weights and volumes may be used, but variations in the method should be described with the results.

·         An average of three determinations is recommended.

Observations and Calculations of xanthan gum as polymer:

According to volume:

             Initial volume (V_o) = 100ml

             Final volume (V_f) = 75ml

             Compressibility index = 100 x [V_o-V_f / V_o]

                                                 = 100 x [100-75/100]

                                                 = 100 x 0.25 = 25%

              Hausner ration = V_o/ V_f

                                                 = 100/75 = 1.33

According to Density:

                      Tapped density = 0.62g/ml

                      Bulk density = 46.5/100 = 0.465g/ml       

                      Compressibility index = 100 x [tapped density-bulk density/tapped density]

                                                                       = 100 x [0.62-0.465/0.62]                            

                                                           = 100 x 0.25 = 25%

              Hausner ratio = tapped density/ bulk density 

                                     = 0.62/0.465 = 1.33

Result:

Ø  Compressibility index of xanthan gum is 25% according to volume r density and Hausner ration is 1.33.According to specification sample is fall in Passable powder range.

Ø  Compressibility index of Tizanidine HCl is 17.07% according to volume and density and Hausner ratio is 1.21. According to specification drug is fall in Fair powder range. (14)

Compressibility Index (%)	Flow Character	Hausner 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

SOLUBILITY ANALYSIS

Phase-solubility analysis is the quantitative determination of the purity of a substance through the application of precise solubility measurements. At a given temperature, a definite amount of a pure substance is soluble in a definite quantity of solvent. The resulting solution is saturated with respect to the particular substance, but the solution remains unsaturated with respect to other substances, even though such substances may be closely related in chemical structure and physical properties to the particular substance being tested. Constancy of solubility, like constancy of melting temperature or other physical properties, indicates that a material is pure or is free from foreign admixture except in the unique case in which the percentage composition of the substance under test is in direct ratio to solubility of the respective components. Conversely, variability of solubility indicates the presence of an impurity or impurities.

Solvents

A proper solvent for phase-solubility analysis meets the following criteria:

1)       The solvent is of sufficient volatility that it can be evaporated under vacuum, but is not so volatile that difficulty is experienced in transferring and weighing the solvent and its solutions. Normally, solvents having boiling points between 60 and 150 are suitable.

2)      The solvent does not adversely affect the substance being tested. Solvents that cause decomposition or react with the test substance are not to be used. Solvents that solvate or form salts are to be avoided, if possible.

3)      The solvent is of known purity and composition. Carefully prepared mixed solvents are permissible. Trace impurities may affect solubility greatly.

4)      A solubility of 10 mg to 20 mg per g is optimal, but a wider working range can be used.

Procedure:

Very soluble	Less than 1g
Freely soluble	1-10
Soluble	10-30
Sparingly soluble	30-100
Slightly solube	100-1000
Slightly solube	1000-10,000
Slightly solube	More than 10,000

·         Take 50ml of purified water.

·         Add amount of solute and dissolve it.

·         Continue dissolving until solute show hinderence to dissolve completely.

·         Temperature rises gradually up to 85

·         Cool down temperature at 80

·         Pippette out 5ml of solution and place it into china dish.

·         Solution was cooled at 70,60,50,40, and 30

·         Evaporate by direct heat all the pipette out solution, for each temperature

·         Weigh all of residues of each temperature separately

·         Maintain temperature solubility profile

·         Calculate solubility of salt at ;

     80=   w₃-w₁       100

                             w₂-w₃

Result:

Xanthan gum is partially insoluble in ethanol and ether and soluble in warm cold and water.

Tizanidine HCl is soluble in water (20 mg/ml). (15)

PARTICLE SIZE ANALYSIS

Sieving is one of the oldest methods of classifying powders and granules by particle size distribution. When using a woven sieve cloth, the sieving will essentially sort the particles by their intermediate size dimension (i.e., breadth or width). Mechanical sieving is most suitable where the majority of the particles are larger than about 75 µm. For smaller particles, the light weight provides insufficient force during sieving to overcome the surface forces of cohesion and adhesion that cause the particles to stick to each other and to the sieve, and thus cause particles that would be expected to pass through the sieve to be retained. For such materials, other means of agitation such as air-jet sieving or sonic sifting may be more appropriate. Nevertheless, sieving can sometimes be used for some powders or granules having median particle sizes smaller than 75 µm where the method can be validated. In pharmaceutical terms, sieving is usually the method of choice for classification of the coarser grades of single powders or granules. It is a particularly attractive method in that powders and granules are classified only on the basis of particle size, and in most cases the analysis can be carried out in the dry state.

Estimate the particle size distribution as described under Dry Sieving Method, unless otherwise specified in the individual monograph. Sieving should be carried out under conditions that do not cause the test sample to gain or lose moisture.

SIEVING METHODS

Mechanical Agitation

Dry Sieving Method:

·         Tare each test sieve to the nearest 0.1 g.

·         Place an accurately weighed quantity of test specimen on the top (coarsest) sieve, and replace the lid. Agitate the nest of sieves for 5 minutes.

·         Then carefully remove each from the nest without loss of material.

·         Reweigh each sieve, and determine the weight of material on each sieve.

·         Determine the weight of material in the collecting pan in a similar manner.

·         Reassemble the nest of sieves, and agitate for 5 minutes. Remove and weigh each sieve as previously described.

·         Repeat these steps until the endpoint criteria are met (see Endpoint Determination under Test Sieves). Upon completion of the analysis, reconcile the weights of material.

·         Total losses must not exceed 5% of the weight of the original test specimen.

·         Repeat the analysis with a fresh specimen, but using a single sieving time equal to that of the combined times used above.

·         Confirm that this sieving time conforms to the requirements for endpoint determination. When this endpoint has been validated for a specific material, then a single fixed time of sieving may be used for future analyses, providing the particle size distribution fall within normal variation.

·         If there is evidence that the particles retained on any sieve are aggregates rather than single particles, the use of mechanical dry sieving is unlikely to give good reproducibility, and a different particle size analysis method should be used.

Result:

By passing sample powder through sieve number 20, 60, 80 then results are;

·        100% pass through sieve number 20

·        100% pass through sieve number 60

·        98% pas through sieve number 80 (16)

DETERMINATION OF MELTING POINT

“For Pharmacopeial purposes, the melting range, melting temperature, or melting point is defined as those points of temperature within which, or the point at which, the first detectable liquid phase is detected to the temperature at which no solid phase is apparent”

A melting transition may be instantaneous for a highly pure material, but usually a range is observed from the beginning to the end of the process. Factors influencing this transition include the sample size, the particle size, the efficiency of heat diffusion, and the heating rate, among other variables, that are controlled by procedure instructions. In some articles, the melting process is accompanied by simultaneous decomposition, which is visually evidenced as a side event like darkening of the material, charring, bubbling, or other incident. The visual impact of this side reaction frequently obscures the end of the melting process, which it may be impossible to accurately determine. In those circumstances, only the beginning of the melting can be accurately established; and it is to be reported as the melting temperature.

CAPILLARY TUBE METHOD:

Apparatus: A suitable melting range Apparatus consists of;

·         Glass container for a bath of transparent fluid,

·         A suitable stirring device,

·         An accurate thermometer

·         A controlled source of heat.

·         The bath fluid is selected with a view to the temperature required, but light paraffin is used generally and certain liquid silicones are well adapted to the higher temperature ranges.

·         The fluid is deep enough to permit immersion of the thermometer to its specified immersion depth so that the bulb is still about 2 cm above the bottom of the bath.

·         The heat may be supplied by an open flame or electrically.

·         The capillary tube is about 10 cm long and 0.8 to 1.2 mm in internal diameter with walls 0.2 to 0.3 mm in thickness.

Procedure:

·         Reduce the substance under test to a very fine powder, and, unless otherwise directed, render it anhydrous when it contains water of hydration by drying it at the temperature specified in the monograph, or, when the substance contains no water of hydration, dry it over a suitable desiccant for not less than 16 hours.

·         Charge a capillary glass tube, one end of which is sealed, with a sufficient amount of the dry powder to form a column in the bottom of the tube 2.5 to 3.5 mm high when packed down as closely as possible by moderate tapping on a solid surface.

·         Heat the bath until the temperature is about 30 below the expected melting point.

·         Remove the thermometer, and quickly attach the capillary tube to the thermometer by wetting both with a drop of the liquid of the bath or otherwise, and adjust its height so that the material in the capillary is level with the thermometer bulb.

·         Replace the thermometer, and continue the heating, with constant stirring, sufficiently to cause the temperature to rise at a rate of about 3 per minute. When the temperature is about 3 below the lower limit of the expected melting range, reduce the heating so that the temperature rises at a rate of about 1 to 2 per minute. Continue heating until melting is complete.

·         The temperature at which the column of the substance under test is observed to collapse definitely against the side of the tube at any point indicates the beginning of melting, and the temperature at which the test substance becomes liquid throughout corresponds to the end of melting or the melting point. The two temperatures fall within the limits of the melting range. If melting occurs with decomposition, the melting temperature corresponding to the beginning of the melting is within the range specified.

Result:

Melting point of xanthan gum is 270^oC

Melting point of Tizanidine HCl is 280⁰ (17)

STABILITY ANALYSIS

Stability: Stability is defined as the extent to which a product retains, within specified limits, and throughout its period of storage and use (i.e., its shelf-life), the same properties and characteristics that it possessed at the time of its manufacture. Five types of stability generally recognized are shown in the accompanying table.

DETERMINATION OF STABILITY AGAINST HEAT:

Theory:

Preparation of stable pharmaceutical product is critical. In every case either prepares alone drug or combination of drug, drug stability testing at various temperatures, different humidity level and in exposure of light. These stability parameters are essential fir asses the stability of drug.

Apparatus:

·         Petri dish

·         Oven

Procedure:

·         Take 2g of powder in a Petri dish and place in oven at temperature of 45⁰C for 2hours.

·         Calculate the percentage purity of sample.

DETERMINATION OF STABILITY AGAINST LIGHT:

Theory:

Preparation of stable pharmaceutical product is critical. In every case either prepares alone drug or combination of drug, drug stability testing at various temperatures, different humidity level and in exposure of light. These stability parameters are essential fir asses the stability of drug.

Apparatus:

·         Petri dish

·         Watch glass

Procedure:

Take some powder in a petri dish place in sunlight for 2hours. Perform assy if drug is given previously to calculate the % age purity.

DETERMINATION OF STABILITY AGAINST MOISTURE:

Theory:

Preparation of stable pharmaceutical product is critical. In every case either prepares alone drug or combination of drug, drug stability testing at various temperatures, different humidity level and in exposure of light. These stability parameters are essential fir asses the stability of drug.

Apparatus:

·         Desicator

·         China dish

Procedure:

·         Take an empty china dish and weigh it. Now places some powder on it and weighed again.

·         Calculate the weight of powder and placed in a desicator containing water.

·         Leave the desicator for 2hours and after it took the dish out, weighed the powder again.

·         Calculate net weight gain from above observation.

Assay:

To study stability calculates %age purity by performing assay from previous procedure of assay of tizanidine. (18)