Systemic treatment is needed if a skin condition is associated with systemic disease, or if the medicament of choice is inactive topically (e.g. griseofulvin). The principles of systemic therapy in dermatology are no different from those in other branches of medicine:
some drugs act specifically, others non-specifically. For example, antihistamines (H1 blockers) act speci-fically in urticaria, and non-specifically, by a sedative effect, on the most common skin symptomaitch.
Systemic disease coexists with skin disease in several ways . Sometimes a systemic disease such as systemic lupus erythematosus may cause a rash; at other times, a skin disease causes a systemic upset. Examples of this are the depression that occurs in some patients affected with severe rashes, and high-output cardiac failure, which may occur in exfoliative dermatitis from the shunting of blood through the skin. A systemic upset caused by skin disease can be treated with drugs designed for such problems while the skin is being treated in other ways.