Stamping a case of cutaneous adverse drug reaction: Proving beyond causality assessment

Different types of skin testing with a suspected drug have been reported to be helpful in determining the cause of cutaneous adverse drug reactions (CADRs). It is of utmost importance for practicing dermatologists to have a first hand knowledge of different types of skin tests available in a case of CADR. In each suspected case, a detailed investigation with the suspected agent and correlation of the positive skin reaction with clinical variant of CADR is advocated. Drug skin tests are performed 6 weeks to 6 months after complete healing of the CADR. Drug patch tests are performed similar to the methods used in patch testing in studying contact dermatitis. The commercialized form of the drug used by the patient is tested at 30% dilution. The pure drug is tested at 10% dilution. In severe CADR, drug patch tests should be performed at lower concentrations. It is also of value to test on the most affected site of the initial CADR.