Elementary tools of Pharmacodynamics
Receptors: protein molecules including enzymes, transporters and ion channels where a ligand (specific endogenous neurotransmitter/hormone or an external pharmacological agent (drug)) binds to, resulting in a cellular response.
- Unique Exception: Orphan Receptors are receptors for which the ligand remains unknown.
- Reminder: Ligand is an ion or molecule that forms a complex with a biomolecule to serve a specific biological purpose
DRUG: A chemical agent that selectively interacts with specific target molecules (i.e. receptors) to alter their specific physiological functions.
- Agonist: drug that activates receptors to result in either stimulation or inhibition of the function of various types of cells and organs.
- Antagonist: drug that prevents receptor activation by agonists.
Drug-Receptor Binding: drugs bind to their respective receptor in a variety of ways depending on their characteristics.
- Ionic interaction: cation & anion
- Hydrogen bonding
- Lipophilic interaction
- Covalent bond: irreversible
FACTORS GOVERNING DRUG ACTION: All drugs are chemicals but not all chemicals are drugs. For a drug to produce a physiologic effect it must first bind to a receptor. Two factors, related to the chemical nature of a drug, determine the interaction of drugs with receptors and hence the effect a drug will have on physiologic processes.
- Affinity is a measure of the tightness with which a drug binds to the receptor.
- Intrinsic activity is a measure of the ability of a drug that is bound to the receptor to generate an activating stimulus and produce a change in cellular activity.
- Both agonists and antagonists can bind to a receptor. However, only agonist molecules can activate the receptor.
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