Pharmacodynamics (J2)

Pharmacodynamics: How Drugs Act

1. Receptors for Drug Action:

> Ligand: a molecule that binds to another molecule.
> Receptor: a molecule (usually a membrane-spanning protein -- a complex chain of amino acids) of a cell that provides the site(s) where neurotransmitters induce their effects.
> Usually only one neurotransmitter is specific enough to fit (or bind) to a specific receptor.
> A drug may be more specific for a receptor than its neurotransmitter.
> Neurotransmitters (& drugs) are held in place by (reversible) ionic attractions: electrostatic attraction of oppositely charged ions ).
> Signal intensity of the (transmembrane) signal depends on the % of receptors that are occupied.
> A drug can affect the signal by binding to either a receptor or to a nearby site.
> Agonistic action: The drug mimics the action of the neurotransmitter.
> Antagonistic Action: The drug blocks access to the binding site for the neurotransmitter.

2. Dose-Response Relationships:

> Potency: the absolute number of molecules of drug required to elicit a response.
>Efficacy: the maximum effect obtainable.
>Variability & Slope refer to individual differences in drug response.
> Most psychoactive drugs are NOT used to the point of maximum effect. Toxic effects (side effects) limit the upper range of dosage.

3. Drug Safety & Effectiveness:

>Individual response to any drug is variable. The distribution of responses usually follows a Gaussian distribution (bell curve).
> The dose of any drug must be individualized.
> Drugs interact. The effects of taking one drug may be modified by the taking of another drug.
> All drugs can produce harmful or toxic effects. Some toxic effects are predictable; others are unexpected -- such as a severe allergic reaction.
> Placebo: a pharmacologically inert substance that elicits a significant therapeutic response. (Work best on symptoms that wax and wane -- such as depression & pain.)
> Placebos can empower patients to stimulate their psychophysiological self-regulation ability. Placebo effect can be similar to and as long-lasting as a drug effect.
> The placebo effect is a powerful element in drug-induced responses -- in fact, in any healing.