The challenge of drug-rechallenge: Facts and controversies.

The accurate identification of the culprit drug inducing a patient's cutaneous adverse drug reaction is important to avoid future adverse reactions and to provide safe alternative drugs. The assessment has to rely on the clinical signs, the time course, and response to treatment. Sometimes, additional diagnostic procedures are also needed. If diagnostic procedures such as in vivo skin testing and in vitro laboratory tests do not lead to conclusive results, confirmation of a presumptive diagnosis by a rechallenge test is often the only reliable way to establish a diagnosis. This procedure should be undertaken only with great caution and a compelling need, because a rechallenge test might cause severe or even fatal reactions. Contraindications and ethical considerations should be taken into account and an individual risk-benefit calculation must be performed in every case.