Section 18. 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. Exanthems (erythematous, morbilliform or maculopapular), urticaria, fixed drug eruptions, and erythema multiforme are the most common. Figure 18-1 is an urticarial reaction from Augmentin and Fig. 18-2 shows a morbilliform eruption from ampicillin. Constitutional symptoms of low-grade fever and malaise may be associated with such drug eruptions. Morbilliform eruptions from ampicillin are more frequently seen in children with infectious mononucleosis.

Drug eruptions may mimic nearly the entire range of dermatoses of other causes. One of the commonest forms is the exanthematic, whose lesions are usually erythematous and edematous. Common causes of drug eruptions include ampicillin, cephalosporins, semisynthetic penicillins, and barbiturates. We have just illustrated cases that were morbilliform. Illustrated here are cases clinically resembling erythema multiforme. Figure 18-3 resulted from a sulfonamide and Fig. 18-4 from a chloroquine (Plaquenil). Note again the tendency to universality and symmetry. Drug eruptions of the types so far illustrated may be uncomfortably pruritic and attended at their onset by prodromal malaise, but they are rarely serious and usually subside fairly quickly upon elimination of the causative drug and, on occasion, even in the face of continued administration of an absolutely required drug.

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 several drugs that are well known for their propensity to cause fixed drug eruptions, namely, phenolphthalein, salicylates, phenacetin, barbiturates, antipyrine, arsenicals, and gold salts. The clinical morphology of a fixed drug eruption is usually a roundish plaque that is palpably edematous and purplish. Sometimes fixed drug eruptions are bullous. Both illustrations here are of fixed drug eruptions caused by phenolphthalein.

This cutaneous change appeared after institution of treatment of an unrelated condition with an antihistamine. The proof of a drug as cause of an ...