Emulsion and creams: Advantages and disadvantages

Pharmaceutical emulsions/creams are commonly used pharmaceutical products that are primarily prescribed for the treatment of external disorders
Pharmaceutical emulsions/creams are commonly used pharmaceutical products that are primarily prescribed for the treatment of external disorders. In addition to this use emulsions are clinically used for total parenteral nutrition, for the oral administration of therapeutic agents and for the rectal administration of antiepileptic agents. The terms emulsions and creams refer to disperse systems in which one insoluble phase is dispersed as droplets within a second liquid phase.

The rheological properties (and hence the structure of the network within the formulation) of the two systems differ considerably. Creams are pseudoplastic systems with a greater consistency than, for example, oral or parenteral emulsions.

There are two principal types of emulsion/cream, termed oil in water (o/w) and water in oil (w/o). In the former system the oil (or internal) phase is dispersed asdroplets through the external aqueous phase. Conversely, in w/o emulsions, the internal phase is composed of water droplets and the external phase is non-aqueous. In addition to the emulsion types described above there are further more structurally complex types, termed multiple emulsions. These are termed water in oil in water (w/o/w) and oil in water in oil (o/w/o) emulsions. 

However, the pharmaceutical uses of these are extremely limited due to their possible reversion to the parent primary emulsion. For example, an o/w/o emulsion may revert to a w/o emulsion. As the reader will observe later in this chapter, the nature of the excipients and the volume ratio of the two phases used in the formulation of these systems determine both the type and consistency of the emulsion.

Emulsions and creams, akin to pharmaceutical suspensions, are fundamentally unstable systems, which, in the absence of emulsifying agents, will separate into the two separate phases. The emulsifying agents used are principally surface-active agents. O/w emulsions may be administered topically or orally whereas the use of w/o creams is principally (but not exclusively) limited to formulations designed for topical application.

Advantages of pharmaceutical emulsions

    Pharmaceutical emulsions may be used to deliver drugs that exhibit a low aqueous solubility. For example, in o/w emulsions the therapeutic agent is dissolved in the 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 compactor formulations.
      Pharmaceutical emulsions may be used to mask the taste of therapeutic agents, 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 flavouring agents.
        Emulsions may be commonly used to administer oils that may have a therapeutic effect. For example, the cathartic effect of oils, e.g. liquid paraffin, is enhanced following administration to the patient as droplets within an o/w emulsion. The taste of the oil may be masked using sweetening and flavouring agents.
          If the therapeutic agent is irritant when applied topically, the irritancy may be reduced by formulation of the drug within the internal phase of an o/w emulsion.
            Pharmaceutical emulsions may be employed to administer drugs to patients who have difficulty swallowing solid-dosage forms.
              Emulsions are employed for total parenteral nutrition.


                Pharmaceutical emulsions are thermodynamically unstable and therefore must be formulated to stabilise the emulsion from separation of the two phases. This is by no means straightforward.
                  Pharmaceutical emulsions may be difficult to manufacture.

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