Pharmacodynamics Principles PDF

PREPARED BY: REYSAN S. COSAS  Pharmacodynamics (PD) is the division of Pharmacology that describes the action of drugs. It includes the measurement of responses to drugs and how response relates to drug dose or concentration. Simply, the term answers the question, "what the drug does to the...

PREPARED BY: REYSAN S. COSAS  Pharmacodynamics (PD) is the division of Pharmacology that describes the action of drugs. It includes the measurement of responses to drugs and how response relates to drug dose or concentration. Simply, the term answers the question, "what the drug does to the body"?  STIMULATION-drugs may increase or enhance the function of an organ or a system. DEPRESSION-drugs inhibit or decrease the function of an organ or the system. IRRITATION-this is an action attributed to the local effects of the drug on a tissue or cell. OTHERS Replacing deficiency of an essential chemical -action of vitamins, minerals, or other supplements; or, Killing/Weakening invading microorganism/rapidly proliferating cells - action of antiinfectivesand antineoplastics  PRIMARY -intended; it is usually the desired effect that leads to its therapeutic use SECONDARY -is unintended; commonly leading to undesired effects 1. Structural nonspecific Alter the cell environment by physical or chemical processes 2. Structural specific Alter cell function by drug-receptor interactions The majority of drugs' action is through this mechanism MECHANISM DEFINITION RESPONSE COMPONENTS Interaction with drug’smolecular The drug target (receptor, ion channel, enzyme, Molecular target carrier molecule The biochemicals linked to drug target (ion Cellular Transduction channel, enzyme G protein) Electrogenesis, contraction secretion, metabolic Tissue An effect on tissue function activity, proliferation Integrated systems including linked systems (e.g. System An effect on system function NS, CVS)  Langley andErlichfirst proposed thatdrug actionswere mediated by chemicalRECEPTORS. Any target molecule with which a drug molecule has to combine in order to elicit its specific effect It is the component of a cell or organism that interacts with a drug and initiates the chain of events leading to the drug's observed effects. Ligand refers to any molecule which attaches selectively to particular receptors or sites AFFINITY-is the capacity of a drug to form the complex with its receptor (DR complex), e.g., the key entering the hole of the lock has got an affinity to its levers INTRINSIC ACTIVITY (OR) EFFICACY -it is the ability of a drug to trigger the pharmacological response after making the drug-receptor complex  AGONIST -refers to an agent that activates a receptor to produce an effect similar to that of the physiologic signal molecule. It has both high affinity as well as high intrinsic activity, therefore can trigger the maximal biological response PARTIAL AGONIST -an agent that activates a receptor to produce a submaximal effect but antagonizes the actions of a full agonist. It has full affinity but with low intrinsic activity and hence is only partly as effective as an agonist.  INVERSE AGONIST -decreases the number of activated receptors to below that observed in the absence of drug. Thus, inverse agonists have an intrinsic activity less than zero, reverse the activity of receptors, and exert the opposite pharmacological effect of agonists. ANTAGONIST -an agent that prevents the action of an agonist on a receptor but doesn’t have any effect of its own. It has only affinity but no intrinsic activity. This drug binds to the receptor and blocks the binding of an endogenous agonist.  Receptors largely determine the quantitative relations between dose or concentration of drug and pharmacologic effects Receptors are responsible for the selectivity of drug action Receptors mediate the actions of pharmacologic agonists and antagonists