Potency of a drug refers to -

Ans. is 'c' i.e., Dose that tequires to produce response o Generally, the intesity of response increases with increase in dose and dose-response curve is a rectangular hyperbola. This is bacause drug-receptor interaction obeys law of mass action. If, however the dose is plotted on a log arithmic scale (log dose-response curve), the becomes sigmoid and a linear relationship between log of dose and the response is seen only in intermediate zone (30-70% response).o Dose response curve can determine three important parameters :A. Efficacy# It refers to maximal response (effect) that can be elicited by the drug.# The upper limit of the DRC (dose response curve) is the index of drug efficacy.# Efficacy is more decisive factor than potency in the choice of the drug.# In case of'non-competitive' inhibitor, there will be flattening of DRC, i.e. efficacy will decrease without a change in potency.B. Potency# It refers to the amount of drug needed to produce a certain response.# The position of DRC on the dose axis (X-axis) is the index ofpotency.# A DRC positioned rightward indicates lower potency, i.e. more dose is required to produce the effect.# Drug producing same response at lower dose are more potent and are on left side of DRC.# In case of'competitive9 inhibitor curve will shift to right Le. potency will decrease without a change in efficacy \C. Slope# If the DRC is steeper, that means the response will increase dramatically with slight increase in dose.# Thus, drugs with steeper DRC have harrow therapeutic index.