Figure 3-35 Dose or concentration versus response. A sigmoidal concentration-response curve is generated when the log drug concentration is plotted against the clinical response or effect. The concentration-response curve is shifted to the right (B to C) in the presence of a competitive antagonist or desensitization. Curve C may also represent an agonist with a lower receptor affinity (K_a ) or potency than curve B. Curve A represents an agonist with higher receptor affinity or potency than curve B.