Diagnosis, Investigation and Management of Non-immediate (Type IV) Cutaneous Adverse Drug Reactions.

Pathophysiologically, drug hypersensitive reactions (DHRs) are classified into four types: type I, immediate reactions, and types II, III, and IV, non-immediate reactions. They are further categorized as severe or non-severe based on clinical severity. Genetic predisposition and viral reactivation are cofactors of severe DHR type IV. Rapid identification, cessation, and future avoidance of offending and cross-reactive drugs are the cornerstone of treatment. The diagnosis is established based on the history, physical examination, and subsequent in vivo, in vitro, and drug provocation testing, which are selected based on the severity of DHR. In non-severe DHRs, desensitization to the offending drug is possible.