PHARMACODYNAMIC INTERACTIONS IN PSYCHOPHARMACOLOGY
When it comes to combining two or more psychoactive compounds, various factors influence how they interact with one another. There are different types of drug/drug & drug/herb interactions which directly affect the way and efficiency at which each compound is able to function.
Its crucial to note that in addition to pharmacodynamic interactions and underlying factors, other types of interactions which will be covered in a separate article, also play a major role in the actions and side effects of any given substance. Those interactions are also involved with pharmacokinetic mechanisms, involving the absorption, transport, distribution, enzymatic metabolism via Cytochrome 450 enzymes, as well as kidney and bile excretions.
Each drug’s binding affinity determines its effect on a given receptor. This affinity has to do with the likelihood that the drug can occupy a receptor. Additionally, the intrinsic efficacy dictates the degree to which a ligand is able to activate or block different receptors and hence producing a cellular response. The affinity and the level of activity of each compound is directly linked to its chemical structure.
Ligands have the capability to bind to specific molecular regions located on receptor macromolecules, known as recognition sites. The exact binding site for a drug may either be identical or different compared to that of an endogenous hormone or neurotransmitter agonist or antagonist.
AGONISTS & ANTAGONISTS
Drugs that either competitively or non-competitively activate a certain receptor are known as agonists. Various neurotransmitters including acetylcholine, norepinephrine and histamine can act as agonists. Similarly, medications such as morphine, all benzodiazepines and barbiturates are also considered agonists, albeit for different receptors.
Inverse agonists bind to the same receptor as an agonist, but produce an opposite pharmacological effect, similarly to competitive antagonists. Despite having an opposite action than an agonist, their effects can be blocked by antagonists for the same receptor. In contrast, neutral antagonists have no effect on their own but can readily block the effects of both agonists or inverse agonists.
In contrast, silent antagonists are thought to have zero affinity for a receptor but is capable of competitively or non-competitively block the actions of both agonists and inverse antagonists. These are the true antagonists. But in most cases where the word antagonist is used, an inverse agonism dependent on dosage and significance rrgsrding binding affinity is what’s being talked about. A compound which binds to the same site as an agonist but has an oppositional effect and can disable those of an agonist.
