Anaphylaxis Autoimmune / Immunology • Anaphylaxis: severe life-threatening systemic hypersensitivity reaction. Triggers: foods (nuts, shellfish), medications (penicillin, NSAIDs), stings. Epinephrine IM is first-line — never delay for antihistamines. HIV / AIDS Infectious Disease • HIV infection destroys CD4+ T cells. AIDS: CD4 <200 or AIDS-defining illness. ART (antiretroviral therapy) achieves viral suppression. U=U: Undetectable = Untransmittable. PrEP prevents HIV acquisition. Peptic Ulcer Disease Gastrointestinal System • PUD: ulceration of gastric or duodenal mucosa from H. pylori (most common), NSAIDs, or stress (ICU). H. pylori eradication with triple therapy is curative. PPIs provide symptom relief. Pericarditis Cardiovascular System • Pericarditis is inflammation of the pericardium. Sharp pleuritic chest pain relieved by leaning forward. Most cases are viral/idiopathic. Treated with NSAIDs + colchicine.