BIPHASIC LIQUID DOSAGE FORMS

BIPHASIC LIQUID DOSAGE FORMS

Additives used in suspension dosage forms

1. Wetting agents: Some substances (e.g. sulfur, hydrocortisone etc.) are both insoluble in water and are poorly wetted by it. During preparation it is difficult to disperse the clumps and the foam produced on shaking. So wetting agents are used to reduce the interfacial tension between the solid particle and the vehicle and increase wetting of the particle.

e.g.    alcohol,  glycerin, propylene glycols, saponins of quillaia extract etc.

2. Flocculating agents: On standing for a long period the suspension may become difficult to redisperse on shaking. That time, controlled flocculation is required to prevent compact sediment, which is difficult to redisperse. Controlled flocculation can be produced either by,
(i) electrolytes (e.g. potassium citrate, phosphate salts), (ii) surfactants, and (iii) polymers.

3. Suspending agents / Thickening agents: Suspending agents are the substances, which are added to a suspension to increase the viscosity of the continuous phase so that the particles remain suspended for a sufficiently long time and it becomes easy to measure an accurate dose.

                                Due to increase in viscosity of the vehicle, the particles sediment at a much slower rate.

                                e.g. methylcellulose, hydroxy propyl methyl cellulose, sodium carboxymethylcellulose, bentonite, veegum etc.

4. Preservative: The aqueous vehicle may be liable for bacterial growth, so a preservative should be used. e.g. benzoic acid, sodium benzoate, methylparaben, proptlparaben etc. may be used.

5. Organoleptic additives: Colors, sweeteners and flavoring agents may be used to make the oral suspensions more palatable.

                                      Colors:             e.g. Amaranth, Tartrazine, Caramel, and other approved colors

                                      Sweeteners:     e.g. Sucrose

                                      Flavors:           e.g. Peppermint oil, Chocolate flavor, Raspberry syrup etc.

Additives used in emulsion dosage forms

A. Emulsifying agent: The emulsifying agents stabilize an emulsion by various mechanisms. They are also known as emulgents or emulsifiers.

Classification of emulsifiers:

Type	Examples	Mode of action
Hydrophilic colloids	Vegetable source Gum acacia Tragacanth Starch Animal source Wool fat Egg yolk Gelatin Synthetic Methyl cellulose, Hydroxyethyl cellulose,	(i)       They do not reduce the surface tension but forms a rigid film on the oil droplets and form a stable o/w emulsion - thus inhibits coalescence of droplets. (ii)     As an auxiliary emulsifier they increase the viscosity of the continuous phase so that movement of dispersed phase is reduced.
Finely divided solid particles	Colloidal clays: bentonite (aluminium silicate) veegum (magnesium aluminium silicate).	(i)       They tend to absorb at the oil-water-interface and form thick impenetrable films. (ii)     Sometimes increases the viscosity of water (as continuous phase).
Synthetic Surface Active Agents	Anionic Potassium stearate Sodium lauryl sulphate Cationic Cetyl trimethyl ammonium bromide (or cetrimide) Ampholytic N-dodecyl alanine Non-ionic Sorbitan mono-oleate (TWEEN) Polyoxyethylene sorbitan mono-oleate (Polysorbate)	(i)       They form a flexible film on the oil-water interface. (ii)     They lower interfacial tension markedly and this contribute to the stability of emulsion. (iii)    In case of ionic surfactants surface charge is developed, increasing the zeta-potential, which will cause repulsion between two adjacent globules.

Difference between emulsion and suspension

Emulsions	Suspensions
1.       They contain two immiscible liquids, one of which is dispensed as minute globules into the other. 2.       Emulsifying agents are required to make a stable emulsion. 3.       Emulsions are mainly of two types: o/w and w/o. 4.       During storage, freezing should be avoided as it may lead to cracking of emulsion.	1.       They contain finely divided solid particles dispersed in a liquid or semisolid vehicle. 2.       Suspending agents are required to make a stable suspension. 3.       Suspensions are mainly of two types: (i) Flocculated and (ii) De-flocculated. 4.       During storage, freezing should be avoided as it may lead to aggregation of suspended particles.