Adverse Drug Reactions Classification

A 58-year-old man on long-term phenytoin therapy for epilepsy develops fever, rash, lymphadenopathy, and elevated liver enzymes 3 weeks after starting the drug. You suspect drug reaction with eosinophilia and systemic symptoms (DRESS). Which investigation is most specific for confirming the diagnosis?

A 32-year-old woman develops sudden-onset anaphylaxis 15 minutes after receiving intravenous penicillin for pneumonia. She has no prior history of penicillin allergy. Which investigation is most appropriate to confirm the immunological basis of this adverse drug reaction?

A 28-year-old woman develops severe anaphylaxis 10 minutes after receiving intravenous penicillin for a urinary tract infection. She has no prior history of penicillin allergy. Which of the following characteristics does NOT apply to this adverse drug reaction?

A 62-year-old man with hypertension is started on enalapril. After 3 weeks, he develops a persistent dry cough. The cough resolves completely after switching to losartan. Which of the following statements about this adverse drug reaction is NOT true?

A 28-year-old woman with systemic lupus erythematosus develops fever, rash, arthralgia, and lymphadenopathy 2 weeks after starting phenytoin for seizure prophylaxis. Laboratory tests show eosinophilia (8%), atypical lymphocytes, and elevated liver enzymes (AST 180 U/L, ALT 220 U/L). What is the most appropriate immediate next step?