Pharmacology for Anaesthesia and Intensive Care

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Section IBasic principles

1

f 0.5

Kd Drug concentration

(a)

log[concentration]

1

f

(b)

0.5

log KD

Figure 3.3.Dose–response curves. (a) Normal agonistdose–response curve, which is

hyperbolic. (b) This curve is plotted using a log scale for dose and produces the classical

sigmoid shape. (c) A and B are full agonists; B is less potent than A; C is a partial agonist that is

unable to elicit a maximal response.

an inverse agonist and a competitive antagonist is important – an inverse agonist

will favour a shift of equilibrium toward inactive receptors whereas a competitive

antagonist binds equally to active and inactive receptors and simply prevents the

agonist from binding. Inverse agonism was first described at benzodiazepine bind-

ing sites, but such convulsant agents have no clinical relevance, however ketanserin

is an inverse agonist at 5HT2creceptors.