Suspensions: Formulation of flocculated and deflocculated suspensions and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector exam
Methods For Formulation of Suspension:
1-Precipitation method: Three precipitation methods are used:
Organic solvent precipitation: Water insoluble drugs can be precipitated by dissolving them in water- miscible organic solvent and then adding organic phase to distilled water under standard conditions. Organic solvents used are ethanol, methanol, propylene glycol and polyethylene glycol.
Precipitation by pH: The method of changing the pH of medium is more readily accomplished and does not present the same difficulties associated with organic solvent precipitation. This method is applicable only to those drugs in which solubility is dependent on pH value. Examples include Estradiol Suspension and Insulin Suspension.
Double Decomposition: This method involves simple chemistry. Example includes White Lotion (NF XIII)
2-Dispersion Method: In this method, the vehicle must be formulated so that solid phase is easily wetted and dispersed. The use of surfactant is desirable to ensure uniform wetting of hydrophobic solid. The use of suspending agent such as synthetic polymer, natural gums and others maybe indicated depending upon specific application. The actual dispersing of solids may or may not cause particle size reduction. If particle size reduction occurs, the particles obtained may have different solubilities and this may lead to super saturation of the system.
3-Use of controlled flocculation: Controlled flocculation of particles is obtained by adding flocculating agents, which are: Electrolytes, Surfactants, Polymers.
4-Use of structured vehicle: Structured vehicles called also thickening or suspending agents. They are aqueous solutions of natural and synthetic gums. These are used to increase the viscosity of the suspension. These structured vehicles entrapped the particle and reduces the sedimentation of particles. Thus, the use of deflocculated particles in a structure vehicle may form solid hard cake upon long storage. Too high viscosity is not desirable as:
- It causes difficulty in pouring and administration.
- It may affect drug absorption since they adsorb on the surface of particle and suppress the dissolution rate.
- Structured vehicle is not useful for parenteral suspension because they may create problem in syringeability due to high viscosity.
Formulation:
- First the particle size is reduced to a desired size with the help of mill or other equipments.
- The insoluble materials are levigated or grinded to a smooth paste with a vehicle containing the wetting agent.
- All soluble ingredients are dissolved in same portion of the vehicle and added to the smooth paste to get slurry.
- If preparing on small scale, the slurry is then transferred to a graduated cylinder and mortar is rinsed with successive portion of vehicle.
- If preparing on industrial scale, then slurry is transferred to a colloid mill or a disperser or any other equipment to completely wet the particles.
- Then a deflocculated suspension is obtained.
- Decide whether the solids are: Suspended in a structured vehicle, Flocculated, Flocculated and then suspended.
- Add the vehicle containing the suspending agent or flocculating agent.
- Make up the dispersion to the final volume.
- Thus suspension is prepared.
Formulation Components:
1-Suspending agents: Suspending agent are also known as hydrophilic colloids which form colloidal dispersion. Suspending agent form film around particle and decrease interparticle attraction. Most suspending agents perform two functions i.e. besides acting as a suspending agent they also imparts viscosity to the solution. Sodium alginate, Methylcellulose (1-2%), Hydroxyethyl cellulose (1-2%), Hydroxypropyl cellulose(1-2%) Hydroxypropyl methylcellulose (1-2%).
2-Wetting Agents: Hydrophilic materials are easily wetted by water while hydrophobic materials are not. However hydrophobic materials are easily wetted by non-polar liquids. The extent of wetting by water is dependent on the hydrophillicity of the materials. The concentration used is less than 0.5 %.
3-Surfactants: Surfactants decrease the interfacial tension between drug particles and liquid thus liquid is penetrated in the pores of drug particle displacing air from them and thus ensures wetting. Generally, we use non-ionic surfactants but ionic surfactants can also be used depending upon certain conditions. Polysorbate 80 is most widely used due to its following advantages:
- It is non-ionic so no change in pH of medium.
- No toxicity. Safe for internal use.
4-Hydrophilic colloids: Hydrophilic colloids coat hydrophobic drug particles in one or more than one layer. This will provide hydrophillicity to drug particles and facilitate wetting. E.g. acacia, tragacanth, alginates, guar gum.
5-Solvents: The most commonly used solvents used are alcohol, glycerin, polyethylene glycol and polypropylene glycol. The mechanism by which they provide wetting is that they are miscible with water and reduce liquid air interfacial tension. Liquid penetrates in individual particle and facilitates wetting.
6-Buffers: Buffers are the materials which when dissolved in a solvent will resist any change in pH when an acid or base is added. To encounter stability problems all liquid formulation should be formulated to an optimum pH. Generally pH of suspension preferably at 7.4-8.4. Most commonly used buffers are salts of weak acids such as carbonates, citrates, gluconates, phosphate.
7-Preservatives: Naturally occurring suspending agents such as tragacanth, acacia, xanthan gum are susceptible to microbial contamination. This leads to loss in suspending activity of suspending agents, loss of color, flavor and odor, change in elegance etc. Propylene glycol, Disodium EDTA (0.1%), Benzalkonium chloride (0.01-0.02%) Benzoic acid (0.1%).
8- Flavoring agents: They are added to increase patient acceptance. Only sweetening agent are not capable of complete taste masking of unpleasant drugs therefore, a flavoring agents are incorporated. Examples include Acacia, Ginger, Sarsaparilla syrup, Anise oil, Glucose, Spearmint oil.
9-Coloring agents: Colors are obtained from natural or synthetic sources. The synthetic dyes should be used within range of( 0.0005 % to 0.001%). Color aids in identification of the product. The color used should be acceptable by the particular country. Most widely used colors are as follows:
- Titanium dioxide (white), Brilliant blue (blue), Indigo carmine(blue), Amaranth (red), Tartarazine (yellow), Annatto seeds(yellow to orange)
10-Sweetening Agents: They are used for taste masking of bitter drug particles. Sugars such as xylose, ribose, glucose, mannose.
11-Humectants: Humectants absorb moisture and prevent degradation of API by moisture. Examples of humectants most commonly used in suspensions are propylene glycol ,glycerol. Total quantity of humectants should be between 0-10 % w/w.
12-Antioxidants: Ascorbic acid derivatives such as ascorbic acid, erythorbic acid, Thiol derivatives such as thio glycerol, cytosine, acetyl cysteine, Tocopherols.
Multiple choice questions:
1.Methods For Formulation of Suspension are
a)Precipitation method
b)Dispersion Method
c)Use of structured vehicle
d)All of these
2.Which precipitation methods are used in formulation of suspensions?
a)Organic solvent precipitation
b)Precipitation by pH
c)Double Decomposition
d)All of these
3. Water insoluble drugs can be precipitated by dissolving them in water- miscible organic solvent and then adding organic phase to distilled water under standard conditions in
a)Organic solvent precipitation
b)Precipitation by pH
c)Double Decomposition
d)All of these
4.Organic solvents used Organic solvent precipitation is/are
a)ethanol
b)methanol
c)propylene glycol
d)all of these
5.Examples of suspensions formulated by Precipitation by pH method is/are
a)Estradiol Suspension
b)Insulin Suspension
c)White Lotion
d)a and b
6.Example of suspension formulated by Double Decomposition method is
a)Estradiol Suspension
b)Insulin Suspension
c)White Lotion
d)All of these
7.In which method the vehicle must be formulated so that solid phase is easily wetted and dispersed?
a)Precipitation method
b)Dispersion Method
c)Use of structured vehicle
d)All of these
8.Which of the following suspending agents are used in dispersion method?
a)synthetic polymer
b)natural gums
c)both of these
d)none of these
9.Controlled flocculation of particles is obtained by adding
a)flocculating agents
b)suspending agents
c)wetting agents
d)all of these
10.Which of the following are flocculating agents?
a)Electrolytes
b)Surfactants
c)Polymers
d)All of these
11.Structured vehicles are also called
a)thickening agents
b)suspending agents
c)emulsifying agents
d)a and b
12.Suspending agent are also known as
a)hydrophilic colloids
b)hydrophobic colloids
c)both of these
d)none of these
13.Surfactants _____ the interfacial tension between drug particles and liquid.
a)increase
b)decrease
c)has no change on
d)improves
14.The most commonly used solvents in suspensions is/are
a)alcohol
b)glycerin
c)polyethylene glycol
d)all of these
15.Most widely used colors in suspensions is/are
a)Titanium dioxide (white)
b)Brilliant blue (blue)
c)Indigo carmine(blue)
d)All of these
Solutions:
- d)All of these
- d)All of these
- a)Organic solvent precipitation
- d)all of these
- d)a and b
- c)White Lotion
- b)Dispersion Method
- c)both of these
- a)flocculating agents
- d)All of these
- d)a and b
- a)hydrophilic colloids
- b)decrease
- d)all of these
- d)All of these
References:
- Lachman/Lieberman’s The theory and practice of industrial pharmacy, 4th edition page, no. 655, 665, 666, 667.
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