Topical

Topical administration refers to a route of administration whereby drug is applied directly to a body surface. Often, the surface in question is the skin, and the drug would be formulated in a cream, ointment, patch or similar. However, application of drops or sprays to the eyes, ears, nose or other mucous membranes would be considered topical, as would use of an inhaler to apply drug to lung membranes. Generally, high lipid solubility is a desirable property for drugs that are applied to the skin, if absorption is necessary in order for the drug to be effective.

Although absorption into the systemic circulation is almost inevitable after topical application, drug concentrations reached at sites distal to the site of application are usually much lower than they would have been had drug been administered by an enteral route, or injected, at a dose sufficient to achieve effective concentrations within the target tissue. Topical administration may thus be considered a strategy to achieve therapeutic drug concentrations within the target tissue while largely avoiding the likelihood of on-target or off-target side-effects in other tissues and organs. For example, adrenergic agonists used as nasal decongestants are more likely to elevate blood pressure, causing headache, and induce tachycardia when taken orally than when applied directly to the nasal cavity in a spray.