Which term describes the phenomenon where a drug's therapeutic effect diminishes with repeated dosing at the same dose, requiring increased doses for the same effect, due to receptor downregulation?
- A Drug tolerance (pharmacodynamic tolerance) ✓
- B Tachyphylaxis
- C Idiosyncrasy
- D Potentiation
Correct answer: A. Drug tolerance (pharmacodynamic tolerance)
Explanation
Pharmacodynamic tolerance refers to the reduced response to a drug over time due to adaptive changes at the receptor level, including receptor downregulation (reduced receptor number), desensitization (uncoupling of receptor from G-protein), or decreased receptor sensitivity. Tachyphylaxis refers specifically to rapid tolerance developing within a few doses or hours (e.g., ephedrine due to noradrenaline depletion). Tolerance to opioids involves both receptor downregulation and functional uncoupling.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.