BIPHASIC LIQUID DOSAGE FORMS | EMULSIONS | emulsifying Agents |

 BIPHASIC LIQUID DOSAGE FORMS

 

The biphasic systems carries with it two distinct phases. In pharmaceutical practice, these systems are exemplified by emulsions and suspensions and constitute a very important group of preparations for both internal ag well as external use. PThe present discussion is restricted to liquid dosage forms only.

 

 

EMULSIONS



EMULSIONS

An emulsion may be a biphasic system during which one phase is intimately dispersed within the other introduce the shape of minute droplets ranging in diameter from 0.1 um to 100 um. it’s a thermodynamically unstable system, which might be stabilized by the presence of an emulsifying agent – (emulgent or emulsifier). 

The dispersed particles is additionally called the interior phase or the discontinuous phase while the outer phase is termed dispersing phase, external phase, or continuous phase. The emulsifying agents also are called intermediate or interphase. Milk is an example of a natural emulsion. The term emulsion springs from the word emulgeo meaning ‘to milk’.
Emulsions are not any longer official in IP.

 

Pharmaceutical Applications

Emulsions are widely utilized in pharmaceutical systems and practicethe foremost important application of emulsions is to mask thé disagreeable taste of oily liquids by formulating them as oil-in-water emulsions. Emulsions of oils like liquid paraffin and oil enhance? the speed and extent of their absorption from the channel because of 1 fine state of subdivision. Similarly, water-soluble substances having 4 disagreeable tastes is dissolved in water and a water-in-oil emulsion! are often prepared. The water-in-oil emulsion is then further emulsified to yield oil-in-water emulsion. : In such cases, the partition coefficient of thé drug and flavor should even be taken under consideration.

parenteral emulsions, containing some fats and medicinal oils, are formulated for intravenous administration. Cod-liver oil.

oil-soluble vitamins A, D, and K and a few oil-soluble sex hormones are presented in emulsified form. Sterile, stable, intravenous emulsions containing fat, carbohydrate, and vitamins in one formulation are attempted. Such products are particularly useful for patients unable to assimilate these vital materials.

Lotions, liniments, and creams may be formulated as either oil-in-water OF water-in-oil emulsions for external use. The percutaneous absorption of medicaments from emulsion products is claimed to be better than other forms. Water-soluble antiseptics applied as oil-in-water emulsions are better absorbed as compared to their formulations in greasy bases. A shear-thinning emulsion can facilitate the method of penetration of the drug into the skin. The viscosity of such an emulsion is reduced on rubbing.

Emulsions may additionally protect the drugs, which are liable to hydrolysis and oxidation. Emulsions may provide prolonged action of the medicaments. within the variety of an oil-in-water emulsion, ephedrine contains a more prolonged effect when applied to nasal mucosa than when utilized in an oily solution. Some emulsions have also been formulated and presented as aerosols.

Microemulsions also are becoming popular nowadays. These are clear dispersions of oil-in-water or water-in-oil during which the diameter of the dispersed globules ranges from 100 A to 600 A. Being clear products, microemulsions are better accepted than normal emulsions and are free from a number of the steadiness problems of emulsions.

Multiple emulsions (w/o/w) or (o/w/o) are employed in several pharmaceutical applications.
Emulsion Type and Detection
In pharmaceutical practice, one in every of the phases of the emulsion 1S is usually water or solution and therefore the other phase is oil or oily liquid Le. non-aqueous. The form is usually within the kind of finely subdivided globules. Thus the emulsion during which oil is distributed within the variety of finely subdivided globules would be called as oil-in-water (o/w) “emulsion and when water is dispersed in oil it’s called ‘as water-in-oil (Wo) emulsion. In an o/w emulsion, oil (or oily liquid) always constitutes the interior phase, and conversely during a w/o emulsion, water (or “aqueous liquid) always constitutes the interior phase.

( In non-ionic emulsifying agents the molecule consists of a hydrophilic Water-soluble) part and a lipophilic (oil-soluble) part. The hydroxy]

(OH) and ethylene oxide (CH2OCH2) groups impart hydrophilic proper. ties to the compound whereas the long-chain carboxylic acid groups (usually 12 to 18 carbon atoms) impart Jipophilic properties. The molecule gets, adsorbed at the oil/water interface forming a stable emulsifying film with the oil-soluble groups directed towards the oil and water-soluble groups directed towards the water. Therefore, if the effect of the water. soluble part is bigger than that of the oil-soluble part the emulsion be of the o/w type, and a w/o emulsion will result if the oil-soluble par is dominant.

Thus the glycol, glycerol, and sorbitan esters of the carboxylic acids produce w/o emulsions since the lipophilic fatty acid radical is more powerful than the hydrophilic glycol, glycerol, or sorbitan radicles. However the addition of monovalent soaps to those compounds reverses the kind of emulsion, The PEG compounds with the quantity of oxyethylene groups within the molecule over 10, all produce o/w emulsions since the oxyethylene groups confer strong water-soluble properties on the compounds.
Determination of style of Emulsion
Dilution test: Dilution of an emulsion either with oi] or with water can reveal its type. The test is predicated on the actual fact that more of the continual phase will be added into an emulsion without causing the matter of its stability. Thus an o/w emulsion will be diluted with water and a w/o emulsion may be diluted with oil. The addition of water to a w/o emulsion and oil to o/w emulsion would crack the emulsion and cause the separation of the phases.

 

Conductivity test:

In this test, a pair of electrodes connected to a lamp and an electric source are dipped into an emulsion. If the emulsion is o/w type, water conducts the current and the lamp gets lit due to the passage of current between the two electrodes. The lamp does not glow when the emulsion is w/o; oil being in the external phase does not conduct the current. Current is not conducted even when the emulsion is o/w type, when

 

purified water instead of potable water is used in the preparation of emulsion. Why?

 

Dye test:

If a water-soluble dye is added to an o/w emulsion the emulsion takes up the color uniformly. Conversely, if the emulsion is wine type and the dye is soluble in water, the emulsion takes up the color only in the dispersed phase and the emulsion is not uniformly colored monomolecular. This can be revealed immediately by microscopic indications of the emulsion.

 

Fluorescence test:

Many oils exhibit fluorescence when exposed to UV light. When a w/o emulsion is exposed to fluorescent light under 4

 

microscope, the entire field fluoresces. Sporty fluorescence a the indie/ cation of o/w type emulsion. However, all oils do not exhibit fluorescence under UV light and thus the method does not have universal application,

 

Cobalt chloride test:

Filter paper soaked in a cobalt chloride solution and allowed to dry turns from blue to pink on exposure to o/y emulsions. The test may not work for unstable emulsions.

 

Filter paper test:

This test is based on the fact that an o/w emulsion will spread out rapidly when dropped onto filter paper. In contrast, a w/g emulsion will migrate only slowly. This method should not be used for highly viscous creams.

 

 

emulsifying Agents (Emulgents)

A mixture of oil and water may yield a crude temporary emulsion, ‘ which, upon standing, will separate in two distinct phases due to the coalescence of the dispersed globules. Emulgents or emulsifying agents can impart stability to such systems. Thus the choice of an emulgent is a critical factor since the quality and stability of the emulsion system can be directly related to the type of emulgent employed. Emulgents are broadly classified as surfactants like spans and tweens, hydrophilic colloids such as acacia, and finely divided solids e.g. bentonite and veegum. An emulgent, in addition to its emulsifying properties, should be nontoxic and its taste, odor, and chemical stability should be compatible with the product.

 

For the proper selection of an emulgent, the pharmacist must be aware – of

(i) the desirable properties of the emulgent;

(ii) how different emulgents act to provide optimum stability to the system; and

(iii) how can the type or physical properties of the emulsion be affected by the emulgent.

 

Desirable properties of an emulgent are :

(i) it should be able to reduce the surface tension to below 10 dynes/cm;

(ii) it should be adsorbed rapidly around dispersed phase globules to form a complete and coherent film to prevent coalescence;

(iii) it should help in building up an adequate zeta potential and viscosity in the system to impart Optimum stability; and

(iv) it should be effective in a fairly low concentration.

 

 

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