Pharmacology Part 2 - Pharmacodynamics PDF
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Dr.Ahmed salam
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Summary
These lecture notes cover pharmacodynamics, which is the study of how drugs affect the body. Topics include drug-receptor interactions, potency, efficacy, and the therapeutic window. The document also discusses drug action mechanisms and types of drug tolerance.
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GENERAL PHARMACOLOGY Part 2 PHARMACODYNAMICS DR.Ahmed salam M.B.CH.B/F.I.C.M.S A&IC Pharmacodynamics: the study of how drug affect the body, involving the concept of potency , efficacy and the therapeutic window. Onset: the point at which the activity of a d...
GENERAL PHARMACOLOGY Part 2 PHARMACODYNAMICS DR.Ahmed salam M.B.CH.B/F.I.C.M.S A&IC Pharmacodynamics: the study of how drug affect the body, involving the concept of potency , efficacy and the therapeutic window. Onset: the point at which the activity of a drug is apparent, time elapsed between administration and the appearance of its pharmacological effects. Peak: the time it takes for a drug to reach its maximum therapeutic response. Duration: refers to the length of time the medication produces its desired therapeutic effect. For example, the duration of oral acetaminophen is four to six hours MECHANISM OF DRUG ACTION a term used to describe how a drug or other substance produces an effect in the body.. 1.Drug-receptor. 2.ion channel. 3.enzyme. 4.carrier molecules. DRUD RECEPTORS Drug receptors are macromolecules typically protiens,that bind a drug and mediate the drug response. Binding of a drug with its receptor result in formation of drug receptor complex (DR) which is responsible for triggering the biological response. D + R = (DR) response Affinity of drug: is a measure of the tightness with which a drug binds to the receptor. Efficacy of drug :is the ability of the drug to induce a therapeutic response. Potency of drug: an expression of the activity of the a drug in terms of the concentration or amount of the drug required to produce a defined effect (how much drug must be administered to elicit a desired response). Ligand : any molecule which attached selectively to particular receptor or sites Drug at Receptor Agonist: Agent which activate a receptor to produce an effect similar to that of the physiological signal molecule. Antagonist: Agent which prevent the action of an agonist on a receptor but does not have any effect of its own. Effect of combination of drugs Addition: response elicited by combined drugs is equal to the combined response of the individual drugs e.g (lidocaine+bupivacaine),(morphine+fentanyl). 1+1=2 Synergism: two drugs with the same effect are given together and produce a response greater than the sum of their response e.g.thiopentone+ alcohol or opioid.opiod + NSAID 1+1=3 Effect of combination of drugs Potentiation: a drug which has no effect enhances the effect of a second drug e.g benserazide+levodopa. 0+1=2 Antagonism: drug inhibit the effect of another drug. Usually the antagonist has no inherent activity e.g (fentanyl+naloxone),(isoprenaline+B.blocker). 1+1=0 Effective Dose 50 (ED50) ED50: the dose that is required to produce a defined therapeutic response in 50% of the population. The ED50 can be considered a standard dose,and it is the dose selected for initial treatment. Lethal Dose LD50: is the dose that is lethal to 50% of animals treated. Toxic dose50 TD50: is the dose that causes adverse effect at an (incidence/severity) not compatible with the targeted indication in 50% of subjects treated. Definitions Side effects: unavoidable ,unintended pharmacodynamic effects that occur at a therapeutic dose. e.g: dryness of mouth with atropine Toxic effects: result of excessive pharmacological action of the drug due to over dosage or prolonged use. e.g: hepatic necrosis from paracetamol over dosage. Drug intolerance: side effects of a drug in an individual at therapeutic doses. e.g: vomiting with a single dose of salicylate. Drug tolerance: decreased response to the same amount of drug after repeated administration. TOLERANCE Patient who are tolerant to a drug require higher doses to produce effects equivalent to those that could be achieved with lower doses There are three types of drug tolerance: 1-pharmacodynamic tolerance, , 2-Pharmacokinetic (metabolic) tolerance 3-tachyphylaxis. Pharmacodynamic tolerance: refers to the familiar type of tolerance associated with long term administration of drugs e.g morphine and heroin It is thought to result from adaptive processes that occur in response to chronic receptor occupation Metabolic tolerance: defined as tolerance resulting from accelerated drug metabolism caused by the ability of certain drug to induce synthesis of hepatic drug metabolizing enzymes. occurs because of a decreased quantity of the substance reaching the site it affects Tachyphylaxis: it is a form of tolerance in which a reduced drug responsiveness caused by repeated dosing over short time (rapidly occurring tolerance to the drug). Unlike pharmacodynamic and metabolic tolerance, which take days to develop, e.g transdermal nitroglycerin. Drug Interaction Drug-drug interaction: A reaction between two (or more) drugs. Drug-food interaction: A reaction between a drug and a food or beverage. Drug-condition interaction: A reaction that occurs when taking a drug while having a certain medical condition. For example, taking a nasal decongestant if you have high blood pressure may cause an unwanted reaction.