Adverse drug reactions and graft-versus-host reaction: unapproved treatments

Cutaneous reactions are among the most frequent side-effects of drug intake. They encompass a wide range of clinical patterns such as macular or maculopapular rashes, urticaria, eczematous or lichenoid lesions, fixed drug eruptions, erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis. The strongest data to establish accurate estimates of rates of cutaneous reactions to drugs come from prospective collected data in population-based studies that monitor large number of patients and capture all adverse events that occur. Despite differences in the design of epidemiologic studies, there is remarkable agreement in the results. Because most drug-induced eruptions appear within the first week after the drug therapy is started, attributing an eruption to a specific drug is often straightforward but it becomes particularly difficult when the patient is taking multiple drugs. In this case epidemiologic studies can be extremely helpful in assessing the likelihood that a certain drug is responsive for that eruption. The most frequent (rashes, urticaria) and the most severe (Stevens-Johnson syndrome, toxic epidermal necrolysis) cutaneous drug reactions are considered here.