An emulsion is a dispersed system containing at least two immiscible (or partially miscible) liquid phases. The two phases of emulsions are stabilized by the presence of an emulsifier. The droplet diameter of the dispersed phase extends from about 0.1 to 10 μM, although particle diameters as small as 0.01 μM and as large as 100 μM are not uncommon.
This article focuses on the advantages and disadvantages of emulsions.
The advantages of emulsions as pharmaceutical products include the following:
1. Pharmaceutical emulsions may be used to deliver drugs that are poorly soluble in water but readily soluble in oils. E.g., in oil-in-water emulsions the drug substance is dissolved in the discontinuous or internal oil phase. Following oral administration the oil droplets (and hence the drug) may then be absorbed using the normal absorption mechanism for oils. Some drugs are more readily absorbed when administered as an emulsion than as other oral comparator formulations.
2. Pharmaceutical emulsions may be used to mask the bitter taste and odor of drugs, in which the drug is dissolved in the internal phase of an o/w emulsion. The external phase may then be formulated to contain the appropriate sweetening and flavoring agents.
3. Drugs that are more stable in an oily phase compared to an aqueous medium can show improved stability in an emulsion dosage form.
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4. Intravenous emulsions of contrast media have been developed to assist in diagnosis.
5. Emulsion can be used to prolong the release of the drug (especially semisolid emulsions) thereby providing sustained release action. The oily phase can serve as a reservoir of the drug, which slowly partitions into the aqueous phase for absorption.
6. Essential nutrients like carbohydrates, fats, and vitamins can all be emulsified and can be administered to bedridden patients as sterile intravenous emulsions.
7. Pharmaceutical emulsions may be employed to administer drugs to patients who have difficulty swallowing solid dosage forms.
8. Emulsions provide protection to drugs which are susceptible to oxidation or hydrolysis.
9. Emulsions are used widely to formulate externally used products like lotions, creams, liniments etc.
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1. Pharmaceutical emulsions are thermodynamically unstable and therefore must be formulated to stabilize the emulsion from separation of the two phases. This is by no means straightforward.
2. Pharmaceutical emulsions may be difficult to manufacture.
3. Storage conditions may affect stability.
4. Bulky, difficult to transport, and prone to container breakages.
5. Liable to microbial contamination which can lead to cracking.
6. Uniform and accurate dose my not be achieved.
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