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Fentanyl is a mu receptor agonist.

Which one of the following options best describes the receptor response to fentanyl?

(Please select 1 option)

The relationship between the dose and response plotted graphically is sigmoid

Intrinsic activity determines maximal response This is the correct answer

Antagonists must have a higher receptor affinity than agonists Incorrect answer selected

Partial agonists usually have low receptor affinity

Maximal response occurs when only when all receptor sites are occupied

Explanation

An agonist is a molecule that has affinity for a receptor and has intrinsic efficacy. Intrinsic efficacy or activity describes the capacity of a drug-receptor interaction to produce a maximal response.

The relationship between the dose and response plotted graphically is a rectangular hyperbola. Antagonists have equal affinity for a receptor but no intrinsic efficacy. Partial agonists have equal affinity for a receptor but partial intrinsic efficacy. If receptor occupancy of a full agonist is plotted against response and then compared with a dose response curve, the functional response lies to the left. This suggests that low receptor occupancy can produce a full response.

Sometimes as low as 5-15% receptor occupancy can produce full response. The remaining 85- 95% of receptors are surplus to requirements.

Reference:

Lambert DG. Drugs and receptors. Contin Educ Anaesth Crit Care Pain. 2004;4:181-184.

Answer Statistics

1

24%

2

51%

3

9%

4

11%

5

8%

Times answered: 240