The therapeutic index (TI) of a drug is: A Its cost B The ratio of the toxic dose to the therapeutic dose (TD₅₀/ED₅₀) C Its half-life D Its bioavailability ✓ Correct Answer: Option B TI = TD₅₀/ED₅₀ (or LD₅₀/ED₅₀). A higher TI means a wider margin of safety. Practice PCAT Exam Prep Quizzes → Browse All Questions Study Flashcards