A 27 year old sexually active male develops a vesiculobullous lesion on the glans soon after within 8hrs taking tablet diclofenac for viral fever. The lesion healed with hyperpigmentation.The most likely dignosis is-

Fixed drug eruption It characteristically recur at the same site following administration of offending drugs or occasionally a member of the same group of drugs. They occur 30min to 8hrs after drug administration Most common drugs: Sulfonamides NSAIDS Dapsone Batbiturates Ciprofloxacin Phenytoin Griseofulvin Metronidazole Antituberculous drugs Pathomechanism Drug induced CD8 positive Tcells induce INFs and TNFalpha dependent damage to keratinocytes Clinical features Single / multiple, round / oval lesions Well demarcated erythematous edematous plaques that resolve with violaceous /hyperpigmented macules Associated burning/ stinging and pruritus Most common sites: oral mucosa; glans penis; hands and feet Bulbous fed: generalised well defines erythematous and bulbous lesions bilateral and symmetrical. Pseudoephedrine causes nonpigmented FDE lesion heal without pigmentation Investigations: oral or topical provocation test. Test drug is taken orally or applied topically Treatment Discontinue the offending drug Coicosteroids: topical and systemic Antihistamines. IADVL textbook of dermatology page 1664