Section 21: Drug Eruptions

Drug eruptions Diagnosing drug eruptions has become a common experience to practitioners in all branches of modern medicine. The profusion of drugs now available, the continuous influx of new drugs, and the capability of drugs to cause actions different from or in addition to their pharmacologically desirable actions make adverse cutaneous reactions an inevitable fact of modern medical practice. The kinds of cutaneous reactions are varied. Illustrated in Fig. 21-1 is a reaction to amoxicillin. Eruptions from amoxicillin are more frequently seen in children with infectious mononucleosis.

Morbiliform rashes are the most common form of drug eruption. Illustrated in Fig. 21-2 is a reaction to chloroquine (Plaquenil). Other common causes are amoxicillin, cephalosporins, semisynthetic penicillins, and barbiturates. Constitutional symptoms of low-grade fever and malaise may be associated with such drug eruptions.

Drug eruptions Drug eruptions may be uncomfortably pruritic, but they are rarely serious and usually subside fairly quickly upon elimination of the causative drug. Illustrated in Fig. 21-3 is reaction to a sulfonamide.

Urticaria multiforme (also Figs. 16-21, 16-22, 16-23) This condition, also known as acute annular urticaria, is a benign and fairly common hypersensitivity reaction that presents with urticarial plaques and annular or arcuate urticarial lesions, along with acral edema. When the cause is a medication, the most likely culprits are amoxicillin, cephalosporins, and macrolides.

Fixed drug eruption Another common type of adverse reaction to drugs is the so-called fixed drug eruption. The term fixed is intended to suggest that the cutaneous change, occurring for the first time in given sites (anywhere), recurs in those same sites upon subsequent and repeated administration. Upon subsequent provocation, new reactions in new sites may occur, but original sites always flare again.

There are a number of drugs that are well known for their propensity to cause fixed drug eruptions. The most common are the tetracyclines, sulfonamides, and, NSAIDs, Other causes are aspirin, dapsone, and a variety of sedatives. The clinical morphology of a fixed drug eruption is usually a roundish plaque that is palpably edematous and purplish as shown in Fig. 21-6. Sometimes fixed drug eruptions are bullous.

Fixed drug eruption Figure 21-7 illustrates fixed drug eruption in a particularly common location. Proof of a drug as cause of an eruption is sometimes certain, on the basis of repeated experience, but ...