Chapter-6
Biphasic Liquid Dosage Form- Suspensions
Syllabus: Suspensions (elementary study)-Suspensions containing diffusible solids and liquids and their preparations. Study of the adjuvant used like thickening agents, wetting agents, their necessity and quantity to be incorporated ,suspensions of precipitate forming liquids like tinctures, their preparations and stability. suspensions produced by chemical reaction. An introduction to flocculated /non-flocculated suspension system.
Suspensions are the biphasic liquid dosage form of medicament in which the finely divided solid particles ranging from 0.5 to 5.0 micron are dispersed in a liquid or semi solid vehicle. The solid particles act as disperse phase whereas liquid vehicle acts as the continuous phase. Suspensions are generally taken orally or by parenteral route. They are also used for external applications.
Qualities of a Good Suspension
(1) It should settle slowly and should be readily re-dispersed on gentle shaking of the container.
(2) The suspension should pour readily and evenly from its container.
(3) It should be chemically inert.
(4) The suspended particles should not form a cake.
(5) It should be free from large particles which spoil its appearance, give a gritty taste to oral preparations and also cause irritation to sensitive tissues when applied externally.
Classification of Suspensions
Suspensions are classified into four main classes according to its pharmaceutical use. These are:-
(1) Oral suspensions
(2) Parenteral suspensions
(3) Ophthalmic suspensions
(4) Suspension for external use
1. Oral suspensions : These suspensions are to be consumed by the patient by oral route. Oral suspensions generally contain flavouring agent and sweetening agent to mask the bitter taste of the drug. They are also made palatable by using a suitable derivatives of drugs e.g., chloramphenicol palmitate suspension is prepared to mask the bitter taste of chloramphenicol. Nowadays suspensions are available in the market in dry powder form and these are reconstituted by adding a specified quantity of freshly boiled and cooled water before use e.g., antibiotics in suspension for paediatric use.
2. Parenteral suspensions: The suspensions which are administered by parenteral route are called parenteral suspensions. suspensions are required to fulfil the following qualities:-
(i) The particle size of the drug should be such that it can be easily pass through the needle of the syringe.
(ii) There should not be any crystal growth in the suspension during its storage.
(ii) The concentration of solid particles in the suspension should be between 0.5 to 5.0 micron.
(iv) The viscosity of the suspension should not interfere with its flow through the syringe needle.
(v) The suspensions should be sterilised.
3. Ophthalmic suspensions : These are not commonly used as compared to eye-drops. These are prepared only in those cases, when the drug is insoluble in the desired solvent or unstable in liquid form. These suspensions must fulfil the following conditions:-
(i) The particle size of the eye-suspensions should be fine enough so that it should be non-irritating to the eye.
(ii) The suspensions should be sterilised.
(iii) These suspension should be isotonic.
(iv) These should have desired viscosity.
(v) The suspension should be packed in a suitable container, so that it can be easily instilled into the eye.
4. Suspensions for external use : These suspensions are meant for external use. e.g., lotions, inhalations, ear drops etc. These suspensions contain very small particles to avoid grittiness. Lotion containing sus- pended particles evaporate when applied to the skin leaving a light deposit of medicament on the surface. Lotions are easier to apply and less messy than many other semi-solid external preparations. Calamine lotion is a suspension type preparation which is applied on the skin to provide protective effect. Lotions which are meant for application on broken or inflamed skin should be free from harmful microorganisms.
Flocculated and Non-flocculated Suspensions: The suspensions are said to be flocculated, when the individual particles are in contact with each other and form a network like structure Whereas in case of non-flocculated suspensions, the individual particle exists as a separate entity.
Formulation of Suspension
1. Flocculating agents : In suspensions, the solid particles are well dispersed in dispersion medium i.e., vehicle. The dispersion can be. improved by adding a surfactant or protective colloid which acts as flocculating agent. The flocculating agent acts by reducing the surface tension and thereby improving the dispersion of solids and minimise flocculation e.g., sodium lauryl sulphate, tweens, spans and carbowaxes, etc. are commonly used as flocculating agents.
2. Thickening agents : These are hydrophilic colloids which form colloidal dispersions with water and increases the viscosity of the continuous phase, so that the solid particles remain suspended in it for a sufficient long time to measure a uniform accurate dose. e.g- gum acacia, tragacanth, starch, sodium alginate, Methyl cellulose, Sodium carboxy methyl cellulose, microcrystalline, clay, aluminium hydroxide, carbomer(carboxy vinly polymer), colloidal silicon dioxide.
3. Wetting agents : These are the substances which reduce the interfacial tension between the solid particles and liquid medium, thus producing a suspension of required quality. This may be achieved by adding a suitable wetting agent which is adsorbed at the solid/liquid interface in such a way that the affinity of the particles for the surround- ing medium is increased and the interparticular forces are decreased. For example, alcohol in tragacanth mucilage, glycerin in sodium alginate or bentonite dispersion and polysorbate in oral and parenteral suspen- sions. The excessive use of wetting agent may cause foaming or may give bad taste or odour to the suspension.
4. Preservatives : A suitable preservative is needed to preserve suspensions against bacterial growth. Preservatives selected should be effective against a wide range of microorganism. Benzoic acid, sodium benzoate, methyl paraben and propyl paraben are commonly used as a preservative in suspensions.
5. Organoleptic additives : Colouring agents, sweetening agents and flavouring agents are generally incorporated in oral suspensions. A suitable perfume and colour is incorporated in suspensions which are meant for external use.
Evaluation of the stability of suspension
1. Sedimentation method
2. Micromeritic method
3. Rheological method
4. Electrokinetic method
Impotant Key Points
* Suspension have particle size range from 0.5 to 5 um
* Brownian motion is shown by particle having size 2 to 5 µm
* Gel to sol and sol to gel phenomenon is called – Thixotrophy
* Concentration at which surfactant form micelle is called - Critical micelle concentration
* Particle size reduction in suspension is done by Levigation method.
* Oily vehicle is used in parenteral suspension while aqueous vehicle is used in oral suspension.
* Sedimentation volume for an ideal or stable suspension is 1
* Sedimentation volume for unstable suspension is 0.
* Non – newtonian fluid viscosity measured by: Cone plate viscometer and Cup & Bulb viscometer
* Newtonian fluid viscosity is measured by: Ostwald viscometer & Falling sphere viscometer.
01. Each mixture below has particles dispersed in water. Which list has the particles increasing in size
(a) Solution, colloid, suspension
(b) Suspension, colloid, solution
(c) Colloid, solution, suspension
(d) Solution, suspension, colloid
02. Which of the following descriptions is correct
(a) A solution consists of a solvent dissolved in a solute
(b) A colloid is a 'cloudy' mixture containing particles which will not easily settle out when the colloid is left standing
(c) A mixture consists of two or more pure substances which can only be separated by chemical methods
(d) A suspension contains particles which will not settle out if the suspension is left standing
03. Which of the following would NOT be described as a colloid
(a) Smoke
(b) Fog
(c) Foam
(d) Saltwater
04. Suspended particles become floccculated in a suspension,because
(a) Particles are closely packed
(b) Attractive forces between particles are appreciable
(C) Repulsive forces between particles are appreciable
(d) Vehicle rejects the particles
05. What is the best description of blood
(a) Sol
(b) Foam
(c) Solution
(d) Aerosol
06. A suspension is formed from uniform particles of solid, of diameter 10 Mm, suspended in a solvent. What is the best description of this system
(a) Monodisperse and coarse
(b) Monodisperse and colloidal
(c) Polydisperse and coarse
(d) Polydisperse and colloidal
07. The scattering of light by coarse and colloidal dispersed systems is known as
(a) Contrast matching
(b) DLVO theory
(c) Tyndall effect
(d) Creaming
08. Brownian movement of particle sedimentation
(a) Assist
(b) Promote
(C) Prevent
(d) Increase
09. Suspension of hydrophobic drug formulated with
(a) Emulsifying agents
(b) Wetting agents
(c) Suspending agents
(d) All of the above
10. Which one of the following systems has the smallest sized domains in its dispersed phase
(a) Nanoemulsion
(b) Coarse suspension
(c) Coarse emulsion
(d) Microemulsion
11. Which of the following is not a mechanism for the separation of a physically unstable suspension of magnesium hydroxide in water
(a) Flocculation
(b) Aggregation
(c) Ostwald ripening
(d) Hydrolysis
12. In the DLVO theory of colloids, normal thermal motion may be sufficient to overcome the energy barrier that leads to irreversible particle aggregation. The name of this energy barrier is which one of the following
(a) Primary maximum
(b) Secondary maximum
(c) Primary minimum
(d) Secondary minimum
13. Colloids can
(a) Scatter light
(b) Not scatter light
(c) Absorb heat
(d) Evolve heat
14. Wetting ability of vehicle is detected by observing
(a) Angle of repose
(b) Contact angle
(c) Critical angle
(d) None of the above
15. Which of the following test is used to compare different suspensions
(a) Physical evaluation
(b) Sedimentation
(c) Rheological evaluation
(d) None of the above
Q. Factors affecting maximumly the Rate of sedimetation of suspension is:
A. Viscosity of medium
B. Particle size
C. Density of particle
D. Gravity constant
Comments
Post a Comment