Topical Product Formulation – Getting the Terminology Right

One little mentioned aspect of topical product development that can be a challenge to client-CRO relations is that of terminology. There are a wide variety of terms used to describe product types; cream, ointment, lotion etc which many people use interchangeably yet, to the formulator each has a very specific meaning. As you can imagine this leads to some confusion and frustration so, in an effort to be helpful we’ve pulled together the following that I hope will be of interest to those embarking on the development of a topical product

Lotions – very low viscosity solutions or suspensions of drug for application to large areas of skin. Typically formulated with volatile materials for a cooling effect and to allow a thin film of drug to remain on the skin surface.

Gels – solutions of drug in a viscous matrix that can be non-aqueous in nature if required. Viscosity enhancement can be achieved by the used of suitable polymers or viscous liquids. Typically the drug loading of gels is up to 2% but this is dependent on the solubility of the drug in the matrix.

Creams – viscous emulsions, usually oil in water. Used mostly with lipophilic compounds that dissolve readily in the oily phase. As with gels the drug loading tends to be low and is dependent on the solubility of the drug in the oily phase which typically is less than 30% of the cream so drug loading can be challenging unless drug lipophilicity is high.

Ointments – extremely viscous suspensions of drug particles in a waxy paste. Used when high drug loadings are required. Can be challenging to apply evenly and frequently have a poor appearance leading to compliance issues.

Sprays – more a means of applying very low viscosity systems such as lotions and creams whose consistency has been lowered to the point that they are more typically referred to as an emulsion.

As you can see from the above, a variety of factors should be considered in selecting the appropriate topical formulation for new chemical entities.

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