Pharmacology Part 2 - Pharmacodynamics PDF

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.