Most Type B ADRs occur within what timeframe after starting therapy (excluding immediate hypersensitivity)?

• A. Within the first day
• B. Within 1 week
• C. Within 4 weeks
• D. Within 12 weeks

Answer: (D)

Type B adverse drug reactions are idiosyncratic, unpredictable, and not related to dose. Their onset depends on individual factors such as immune sensitization or unique metabolic pathways, so they don’t appear immediately after starting therapy. Excluding immediate hypersensitivity, these reactions typically emerge after a latent period of weeks to months. A 12-week window (about 3 months) best captures the common timing for non-immediate Type B reactions, reflecting that the onset is often within weeks to a few months rather than right away. Shorter timeframes miss many cases, while longer ones are less routinely anticipated in standard teaching.