Evaluation of Suspension | Pharmaceutical Suspension

Suspension is such a pharmaceutical formulation that starts settling after a time, then to remove this thing, the bottle of suspension has to be shaken. After the formulation of suspension, many types of tests have to be done, which is called the evaluation of suspension. So, in this article, I will give you complete information about suspension evaluation.

Evaluation of Suspension

Suspension is a coarse dispersion in which insoluble particles of a specified diameter (1 micrometer) are dispersed in a liquid medium that is generally aqueous.

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For the evaluation of suspensions there are following types of tests are being carried out;

(a) Sedimentation Method

For the determination of sedimentation two parameters are studied, which are;

(i) Sedimentation volume
(ii) Degree of flocculation

(i) Sedimentation Volume

The volume of sedimentation is measured with the help of a measuring cylinder.

A 50 ml of suspension formulation is poured into a 100 ml measuring cylinder and put aside.

Now, read the sedimentation volume after 1, 2, 3, and 7 days after that read it for up to 12 weeks at weekly intervals.

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For each formulation there are at least three results are obtained.

Then sedimentation volume is calculated as per the equation given;

F = V_u / V₀

Where,
F = sedimentation volume
V_u = the ultimate height of sediment
V₀  = the initial height of the total suspension

(ii) Degree of Flocculation (β)

The ratio of sedimentation of the volume of the flocculated suspension (F), and the sedimentation volume of the deflocculated suspension, (F∞) is known as the degree of flocculation (β).

β = F/ F∞ = Floculated suspension sedimentation volume / Defloculated suspension 

                sedimentation volume

The value of F ranges from less than one to greater than one

Normally F < 1.

When F < 1 --- V₁ <Vo

When F = 1 --- Vu <Vo

The system is in flocculated equilibrium and shows no clear supernatant on standing.

When F >1 --- V >Vo

The higher the value, the higher will be the stability.

(b) Rheological method

For the stability as well as pourability of suspensions it is very important to prepare a suspension with desired viscosity.

It is known that due to sedimentation and formation of cake, the suspension has lesser physical stability among all the dosage forms.

When the viscosity of the dispersion medium is increased, the terminal settling velocity decreased got decreased because of this the dispersed phase settles at a slower rate, and it remains dispersed for a longer period which yields higher stability for the suspension.

In the same way as the viscosity of the suspension increases, the durability of the suspension got decreases which became an inconvenience to the patients increasing the doses.

If the suspension’s viscosity increases then the pourability of the suspension is decreases which become very inconvenience to the patients for increasing the dose.

Hence, to get stable and easily pourable suspensions the viscosity of suspension should be maintained within the optimum or desired range.

Brookfield viscometer that is mounted on a helipath stand is used in the rheological method.

For descending slowly into the suspension a T-bar spindle is made, and then the resistance that the spindle shows at various levels in sediment is measured in a viscometer reading dial.

The different samples that were stored for a very long period show whether the required changes are needed or not. This measurement is done on undistributed samples that are of different ages. The results show that with time how the particles are settled down.

In the study of screening, if the suspension is of good quality then it shows a lesser rate on the dial reading with the turns of a spindle that is the curve will be horizontal for a longer period.

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(c) Electro Kinetic Method

In the electrokinetic method, the zeta potential is measured with the help of the microelectrophoresis apparatus and zeta plus. Because of this, the stability of the dispersed system is obtained.

Example - Micro-electrophoresis apparatus MK-1

Zeta Potential

With the help of zeta plus the zeta potential of the prepared suspension is measured.

By using the pipette approximately 1ml of suspension is transferred into a plastic cuvette, and diluted with the distilled water.

For the measurement of zeta potential, the Brookhaven zeta potential software is used.

At a temperature of 25°C all the parameters are set and the refractive index should be 1.33.

Now, the zeta potential of the preparation is measured on day 0, day 7, day 14, day 21, and day 28 of the post-formulation.

(d) Micromeritic Method

The particle size of the dispersed phase is determined by the stability of the suspension.

If there are any changes in particle size concerning the time that will give beneficial information about the stability of the suspension.

The change in the particle size distribution as well as the crystal habit may be studied with the help of a microscope and with the help Coulter counter method.

Photo Microscopy Method

To estimate and determine the changes in particle size distribution and crystal form the microscope may be used.

By attaching the Polaroid camera to the piece of the monomolecular microscope the fast processing of photomicrographs is increased.

With the help of photomicrographs, you can determine the stability as well as changes in the physical property of the suspension.

(e) Freeze-Thaw Test

The Freeze-thaw test is determined the tendency of suspension to form crystallization or color.

Freeze-thaw tests the sample is placed in the freezer for up to 18 hours and after that placed at room temperature for up to 4 to 6 hours.

Then repeat this freeze-thaw cycle up upto 10 times.

(f) pH Measurement

In quality control testing the measurement of pH as well as the maintenance of pH is one of the important steps.

There are mainly two types of methods that are used in the measurement of pH.

Methods for pH measurement

For the measurement of pH, dip a piece of pH paper into the sample and match the color of the pH paper to the table specified on the table. This is one of the simplest and cheapest methods that are used in the measurement of pH.

(g) Visual Inspection

By the visual inspection, the ingredients and the final products were examined very carefully

The visual inspection determines the purity and appearance of the final products.

The physical appearance of the products are very important for the patients because if the physical appearance of the products will not be good then it will hamper patient adherence and patient compliance become critical so it should be;

• Looking good and,
• Appearance should be elegance

Evaluation of Suspension Tutorial Video

I hope that you have liked the article on the evaluation of suspension. If you did not understand any point ask in the comment.

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