Pharmacology for Nursing PDF

Pharmacology for Nursing BY Dr. Abeer M.R. Hussein Pharmacodynamics  MECHANISM OF DRUG ACTION A) Receptor mechanisms: 1.Drugs act by binding to specific receptors 2.Drugs may act by inhibition of enzymes 3.Drugs may block an ion channel B) Non-receptor mechanisms: a)Direct chemical...

Pharmacology for Nursing BY Dr. Abeer M.R. Hussein Pharmacodynamics  MECHANISM OF DRUG ACTION A) Receptor mechanisms: 1.Drugs act by binding to specific receptors 2.Drugs may act by inhibition of enzymes 3.Drugs may block an ion channel B) Non-receptor mechanisms: a)Direct chemical interaction: b)Physical or physicochemical properties:  AGONISTS & ANTAGONISTS Endogenous physiological receptors - Some drugs act by binding to receptors which normally act as receptors for endogenous substance as hormones, neurotransmitters, and autacoids. Examples of these receptors: - Cholinergic, adrenergic, dopaminergic, histaminic and opioid receptors. Agonists and Antagonists: - Drugs can either be agonists or antagonists at their receptor sites. Agonists: are drugs that bind to their targets and form a drug-receptor complex producing intrinsic activity. Agonists usually mimic (i.e., produce action similar to the action) of endogenous regulatory substance. Antagonists: are drugs that inhibit the action of endogenous regulatory substances (hormones, neurotransmitters or autacoids).  DRUG ANTAGONISM Definition: Means a decrease in the effect of a drug when combined with another drug. Types: -Pharmacological antagonism. - Chemical antagonism. -Physical antagonism -Physiological or functional antagonism.  Pharmacological antagonism: A-Receptor or pharmacodynamic antagonism: -These antagonists may block the ability of agonists to bind to the receptor -Examples of competitive antagonists: i)Propranolol (beta-blocker) competes with beta- agonist for beta- adrenergic receptors. ii)Prazosin competes with alpha agonist for alpha adrenergic receptors. iii)Atropine competes with acetylcholine at the muscarinic receptors. B-Pharmacokinetic or dispositional antagonism: - Some drugs can decrease effect of other drugs by affecting: absorption, metabolism or excretion  Physiological or functional antagonism - One drug produces physiological action opposite to other drug through action on different receptors. - Example: Epinephrine is physiological antagonist to histamine as epinephrine is bronchodilator, vasoconstrictor and increase in BP whereas, histamine produces bronchoconstriction, vasodilation, and decrease in BP. Both agents bind to different receptors but produce opposite physiological response.  Chemical antagonism: - Chemical interaction between two drugs to neutralize the action of each other as: - Protamine (positively charged) neutralizes heparin action (negatively charged). Physical antagonism: - As activated charcoal causes adsorption of strychnine  DRUG TOLERANCE Definition of tolerance: Tolerance is the decrease in the intensity of response of some drugs after repeated administration. Definition of tachyphylaxis (acute tolerance): It is the rapid development of tolerance after one dose or fewer doses Prevention of tolerance: By stop drug administration for short period (1-2 weeks), then give it in the previous dose.  ADVERSE DRUG REACTIONS - Adverse drug reaction may be predictable or type-A reaction (as sedation with antihistaminics and dry mouth with atropine) or unpredictable or type-B reaction (as in cases of allergy and idiosyncrasy). Types of adverse drug reactions: A) Toxic reactions: 1.Dose-related. 2.Usually reversible. 3.May be: i)Pharmacological: usually extension of the pharmacological action as severe hypotension after overdose of antihypertensive or severe hypoglycemia after overdose of antidiabetics. But the pharmacological reaction may not relate to the main action as in cases of diarrhea with antibiotics. ii)Pathological toxic reaction: as hepatitis, nephrotoxicity iii)Genotoxicity: due to alteration in DNA that causes neoplasm. B) Allergic reactions (hypersensitivity): 1.Dose- independent. 2.Due to previous sensitization of the immune system. 3.The drug acts as hapten (incomplete antigen) and combined with endogenous substance to form antigenic complex which stimulates antibodies formation. -On second exposure, Ag-Ab reaction may occur causing the typical allergic reaction (ranging from skin rash............to anaphylaxis). C) Idiosyncrasy: 1.Abnormal reaction to the drug, either severe reaction in a very small dose or extremely insensitive to high doses. 2.The cause is due to genetic deficiency of enzyme or genetic alteration in the function of receptors. Examples: a)Severe hemolytic anemia with alpha methyl dopa or certain foods: due to deficiency of G-6-P dehydrogenase enzyme. This enzyme is responsible for formation of reduced glutathione that protect RBCs against any oxidizing agent. b) Severe apnea with succinylcholine: due to deficiency of pseudocholinesterase enzyme which responsible for hydrolysis of succinylcholine within 5 minutes.  FACTORS DETERMINING DRUG DOSAGE 1-Body weight and volume of distribution. 2-Age: infants and old age need reduction of adult dose. Calculation of child dose: Child dose = Adult dose × Age of child in years Age in years +12 (OR) Child dose = Adult dose × Weight of child in pounds. 150 3-Sex: female more sensitive to drugs due to small size of the body, endocrinal difference. 4-Race: black race is less sensitive to ACEls (as captopril) 5-Route of administration: oral dose is usually more than parenteral dose. 6-Drug dosage form and formulation. 7-Time of administration: as diazepam causes more hypnotic effect if given at night 8-Pathological factors: as liver, and kidney diseases. 9-Genetic factors: as genetic difference in liver enzymes. 10-Presence of other drugs: as drug interaction may occur. 11-Development of tolerance, tachyphylaxis, or drug resistance. THANK YOU