Tachyphylaxis is best described as?

• A. Rapid increase in response to a drug after repeated dosing.
• B. Prolonged onset of action of a drug.
• C. Rapid decrease in response to a drug after repeated dosing.
• D. Return to baseline after cessation of dosing.

Answer: (C)

Tachyphylaxis is a rapid decrease in response to a drug after repeated dosing. This happens because the body quickly adapts at the level of receptors or signaling pathways—desensitization of receptors, receptor internalization, or depletion of mediators—so the same dose produces a much smaller effect after prior exposure. Because it develops within minutes to hours, it contrasts with tolerance that tends to grow more slowly over days. Clinically, you might see it with nitrates like nitroglycerin, where ongoing use diminishes the drug’s effect and may require dosing adjustments or drug-free intervals. The other patterns—an increasing response with repeated use, a longer onset of action, or a return to baseline after stopping—do not describe tachyphylaxis.