Cutaneous adverse reactions to drugs are common in pediatric
practice and often present a diagnostic challenge.1 The
pathogenesis of most drug eruptions is not well understood. With
the exception of fixed drug eruption (discussed shortly), a diagnosis
of drug causation cannot be based solely on the morphology of the skin
lesions.2 A high index of suspicion is important so that
the offending drug is discontinued and avoided in the future, particularly
in the case of life-threatening reactions such as anaphylaxis, the drug
hypersensitivity syndrome (DHS), and Stevens-Johnson
syndrome (SJS) or toxic epidermal necrolysis (TEN).
Conversely, it is important not to erroneously label a child as “allergic” to
a widely used medication such as penicillin. There are no standardized
laboratory investigations that confirm drug causation, and the value
of allergy testing is largely restricted to cases of immunoglobulin
E (IgE)-mediated penicillin hypersensitivity. Therefore, a detailed
history, evaluation of the morphology of the eruption, consideration
of a differential diagnosis, and careful clinical judgment are essential.
The timing of the reaction may be helpful. Medications begun
recently, particularly within the past weeks, are more likely to
be culpable than drugs taken for many months. Urticaria usually
occurs within hours to 1 day after beginning a medication, whereas
exanthems develop 7 to 10 days into treatment unless there has been previous
exposure. Life-threatening reactions to sulfonamides and anticonvulsants
such as drug hypersensitivity syndrome and SJS/TEN characteristically
occur 1 to 3 weeks after initiating therapy. Although these serious
reactions are rare, the parents of children prescribed these medications
should be advised to seek medical attention if a rash or fever develops
during the first weeks of treatment.
Exanthematous (or morbilliform) drug
eruptions, although often extremely pruritic, are usually
benign and self-limited. They may be difficult to distinguish from
a viral exanthem. Some are the result of a drug-virus interaction
such as occurs when ampicillin is administered to patients with
an Epstein-Barr virus infection; human herpes virus-6 and cytomegalovirus
have also been implicated.
Drug hypersensitivity syndrome or drug reaction with eosinophilia
and systemic symptoms (DRESS) should be considered in all patients
presenting with an exanthematous drug eruption. This is characterized
by a generalized exanthem, facial edema, fever, hepatitis, lymphadenopathy, eosinophilia,
and variable multiorgan disease. Because it is accompanied by fever
and signs of systemic toxicity, this serious and sometimes life-threatening
disorder may be mistaken for a viral or other infectious illness.
Generalized erythroderma with widespread superficial pustules
is seen as a drug reaction to erythromycin, penicillins, and other
medications and is known as acute generalized exanthematous pustulosis (AGEP).
Acute urticarial drug eruptions may be associated
with airway angioedema and anaphylaxis. These life-threatening complications usually
develop shortly after administration of the medication. Urticaria
in childhood is often precipitated by a viral or upper respiratory
tract illness for which the child may have been administered an
antibiotic, and it can be difficult to ascertain whether ...