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PHARMACODYNAMICS & Drug Receptor Interaction

>Pharmacodynamics deals with the biochemical and physiological effect of drug as well as its mechanism of action.                                        OR We can simply define it as, The action of drug on the body.  •Most drug exert effects, both beneficial and harmful, by interacting with specialized target macromollecule called receptor.  Receptor : it refers to the drug binding site in the cell or on the surface of cell which mediate the action of drug.     • There are some drugs which do not require receptors Example = mannitol , anti-helmintic drugs, etc. NATURE OF DRUG RECEPTOR          1. Regulatory protein which mediates the action of endogenous chemical signals. For example : neurotransmitters , harmones and autocoids.           2. Enzymes. For example : dihydrofolic reductase     ...
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Cholinergic neuron & Cholinergic Receptors

 •Drugs affecting the autonomic nervous system(ANS) are divided into two groups according to the type of neuron involved in mechanism of action.    •The cholinergic drugs, which act on receptors activated by acetylcholine(Ach), Where as adrenergic drugs act on receptors stimulated by epinephrine or norepinephrine.    •The cholinergic drugs act by either stimulating or blocking the receptors of the ANS.  The cholinergic neuron   • The preganglionic fibres terminating in adrenal medulla.    • The postganglionic fibres of parasympathetic division use ACh as a neurotransmitter.  The postganglionic sumpayhetic division of sweat glands also uses ACh.    • Ina ddition, cholinergicneurons innervate the muscles of somatic system and play an important role in CNS.  NEUROTRANSMISSION @ CHOLINERGIC NEURON :   • Neurotransmission at cholinergic neurons involves 6 sequential steps :   (1) Synthesis of ACh   (2) Storage of...
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AGONIST & ANTAGONIST with types

AGONIST       • Agonist is a chemical(drug) that binds to the receptor and activates the receptor to produce biological response.                                             OR       • Agonist is a drug that produce effects on endogenous compounds, when it interacts with it’s receptor.     => Agonists are of following types:      (1) Full agonists     (2) Partial agonists     (3) Inverse agonists (1) Full Agonists       • If a drug binds to a receptor and produce maximal biological response that mimics the response to endogenous ligand is called full agonist.   - All full agonists for a receptor population should produce the same E max. For Example : phenylephrine is a full agonist at alpha1-adrenoceptors, because it produce the same E max as the endogenous ligand, norep...
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Review of Routes of Drug Administration

Routes of Administration :       The route of administration is determined by properties of the drug (like Water/Lipid soluble , Ionization) and by therapeutic objectives (like need of rapid onset , need of long term onset or restriction of delivery to local site). => Major route for drug administration are Enteral, Parental, and topical.  1) Enteral :            Enteral administration (adminstering a drug by mouth) is the most common, convenient, and economical method of drug administration.  => The drug may be swallowed, allowing oral delivery, or it may be placed under tongue (sublingual) or between the gums and cheek(buccal), facilitating the direct absorption in to blood stream.                              (1) ORAL :            • Oral administration provide many advantages like:  (i) Most convenient method for ...
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Cholinergic Drugs (Direct acting) Part-1

Cholinergic Agonists (direct acting)  • Cholinergic agonists mimic the effect of acetylcholine by binding directly to cholinoceptors (muscarinic & nicotinic).   • These agents are classified into 2 groups;     (1) Choline esters : it includes endogenous ACh and synthetic esters of choline. Such as Carbachol & Bethanechol .     (2) Naturally occuring Alkaloids : Nicotine & Pilocarpine .    • All direct-actings Cholinergic drugs have longer duration of action than Acetylcholine.    (1) ACETYLCHOLINE   • ACh is the quaternary ammonium compound that cannot penetrates membranes.    • It is nuerotransmitter of parasympathetic, somatic nerves & autonomic ganglia.    • It lacks the therapeutics importance b/c of multiple actions and its rapid inactivation by the cholinesterases.    • ACh has both muscarinic and nicotinic activity.    Functions :     (a) Decrease...
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Drug clearance & Half Life & Dose

Drug Clearance It refers to the ratio of rate of drug elimination to the concentration of drug in biological fluid(C).                       CL = rate of elimination / C Rate of elimination   • For most of the drugs, elimination is not saturable & rate of drug elimination is directly proportional to concentration.                     Rate of elimination = CL x C ==> The difference between drug clearance and drug elimination is that :     • Clearance is Volume of blood cleared of drug per unit time and Elimination is amount of drug cleared from blood per unit time.  Total Body Clearance   • The total body systemic clearance , CLtotal is the sum of all clearances from drug metabolising and drug eliminating organs.                                      ...
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Cholinergic Drugs (direct acting) Part-2

  (3) CARBACHOL (Carbamylcholine )   • Carbachol is is an ester of carbamic acid and poor substrate for AChEsterase. It is biotransformed by other esters at very slow rate.    • Carbachol has both Muscarinic and Nicotinic actions. Functions   (i) Actions :    • Carbachol has profound effects on both Cardiovascular system and GI system.    • It has ganglion stimulating activity and it may first stimulate and then depress these systems.    • It can cause release of epinephrine from adrenal medulla by its nicotinic functions.   On Eye :     • It cause miosis    • It cause spasm of accomodatiom in which the ciliary muscle of the eye remains in a constant state of contraction.    • Carbachol is also used to stimulate micturation by contraction of detrusor muscle. (ii) Therapeutic uses :     • Carbachol has high potency, receptor non-selectivity and relatively long duration of acti...
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Basic Introduction to Pharmacology for beginners

Introduction       Pharamcology is the branch of medicine which deals with study of drugs, it’s effect on body(p harmacodynamics ) and action of body on drug ( pharamcokinetics ).                                            OR Pharmacology is the study of substance that interact with living system through chemical process, by binding to regulatory mollecules & activating or inhibiting normal body processes. Branches of  Pharamcology 1> Pharmacotherapeutics       - Also know as Medical Pharamcology.        - It is science of material used to diagnose, prevent amd treatment of disease.        - It is divided in to 2 branches : Pharamacodynamics and pharmacokinetics       (i) Pharmacokinetics  = It deals with the absorption, distribution, bioatranformation and excreation of drugs a...
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Mechanism of absorption of Drugs

    Absorption of Drugs • Absorption concerns the process of entry of drug in to systemic circulation from site of administration.  •The rate and extent of absorption depend on:   -the environment where the drug is absorbed   -chemical characteristics of drug   -route of administration (which influence bioavailability) • The route of administration other than intravenous may result in partial absorption and lower bioavailability.  (A) Mechanism of absorption of drug from GIT • Depending upon their chemical properties , drugs may be absorbed from GI tract by passive diffusion, facilitated diffusion, active transport or endocytosis.    (1) Passive diffusion :       • In this drug move from area of high concentration to area of lower concentration.                  - also known as non-ionic diffusion    - The driving force for this process is concentration or ...
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Distribution of Drug in simplest way Pharmacology

DRUG DISTRIBUTION       • Drug distribution is the process by which the drug reversibly leaves the blood stream and enters the extracellular fluid and tissues.    - For drugs administered IV, absorption is not a factor and the initial phase immediately following administration represents distribution phase.   - The distribution of the drug from plasma to interstitium depends upon :        (i) cardiac output & local blood flow       (ii) capillary permeability       (iii) degree of binding of drug to plasma & tissue protein       (iv) lipophilicity of drug       (v) Volume of distribution    (1) Blood flow :   • The rate of blood flow to the tissue capillaries varies widely. For instance, blood flow to vessel rich organs (like : brain, liver & kidney) is greater than skeletal muscles, adipose tissues, skin which have lower rates of blood flow....
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