Receptor

Binds drugs, transduces binding into a response

Ligands

Drugs, bind to receptors

K_{D}

K_{D} = k_{2}/k_{1} = [L] * [R]/[LR]

- Equilibrium, dissociation constant
- Describes the goodness of fit between ligand and receptor
- Inversely related to the affinity of ligand for the receptor
- Has units of concentration

Affinity

The ability of the drug to bind to a receptor

R_{T}

R_{T }= [LR] + [R]

Total number of receptors in a cell or tissue (bound and unbound)

Intrinsic activity

(α), measure of the ability of the LR complex to elicit the effect being measured, also called *efficacy*

- Is the ratio of the Emax of the ligand of interest to the Emax of a full agonist
- Full agonist, α = 1
- Antagonist, α = 0

Agonist

Drug with an intrinsic activity (α) of 1

Antagonist

Drug with an intrinsic activity (α) of 0

Partial agonist

Drug with an intrinsic activity (α) between 0 and 1

Spare receptors

Increase the sensitivity of the cell to a low concentration of ligand

Allows for high sensitivity without long activation time

Potency

The relationship between the amount of drug administered and its effect, determines the position of the curve on the x-axis

Determined by:

- Affinity for the site of action
- Ability to reach site of action

Efficacy

Intrinsic activity, the relative ability of a drug-receptor complex to produce a maximum functional response

Determined by:

- Intrinsic activity
- Characteristics of the effector
- Limitations on the amount of drug that can be administered

Maximum efficacy

Maximal effect that is produced by a drug, it is the maximum point on the y-axis that is reached

ED50

the dose that produces the desired effect in half of the population

Hypersensitivity

allergic or inflammatory response to a drug

Hyperreactive

an unusually low dose of drug produces its expected pharmacologic effects

Hyporeactive

require exceptionally large doses of drug to evoke expected pharmacologic effects

Therapeutic index

Ratio of TD50/ED50

The ratio of the dose that produces a toxic effect in half of the population to the dose that produces the desired effect in half of the population

TD50

Median toxic dose

the dose that produces a toxic effect in half of the population

LD50

Median lethal dose

the dose that kills in half of the population

Log-normal distribution

You know what it is.