Receptors Receptor theories 1. Occupation theories A.J.Clark propounded the occupation theory which assumes that the extent to which a tissue is dependent on the proportion of its receptor population that has been occupied by a drug and maximal response is reached when all the receptors are occupied. He presumed that each occupied receptor delivered a constant […]
Pharmacodynamics of drugs Pharmacodynamics is the study of the biochemical and physiological effects of drugs and their mechanism of action. It is the response of the organism to the action of a drug in the absence of a disease. Pharmacodynamics is ‘what the drug does to the body’. Principles of drug action Drugs do not impart new
Excretion of drugs Drugs are excreted mainly by the kidneys into the urine and by the liver into the bile and subsequently into the feces. Alveolar elimination is of major significance when inhalant anesthetics are used. The main factors governing elimination by this route are concentration in plasma and alveolar air and the blood/gas partition
Bio-transformation of drugs The chemical alteration of drugs in the body Sequelae of biotransformation reactions General Pattern of biotransformation is biphasic. these phase 1 and phase 2 described below- 1. Phase-I Biotransformation – oxidation reactions and others Although every tissue has some ability to metabolize drugs, the liver is the principal organ of drug metabolism.
Distribution of drugs Distribution of drug is the drugs taken throughout the body by bloodstream Once absorbed, it gets distributed to other tissues which had no drug. Factors that govern distribution of drug Blood flow rate limiting step in distribution – Highly perfused organs such as Liver, Kidney, GI tract, Brain, Lungs receive rapidly high levels
Absorption of drugs Absorption is the movement of drug from the site of administration to circulation. Often the entire quantity of administered drug does not reach the systemic circulation. Only the fraction of drug that was absorbed is available for action. During the process of absorption, the quantity of drug absorbed and also the rate
Pharmacokinetics of drugs Pharmacokinetics is the study of the actions of the drugs in the body over a defined period of time. It deals with the absorption, distribution, biotransformation and excretion of the drug. Pharmacokinetics is ‘what the body does to the drug’. Importance of kinetic study For arriving at the dosage regimen (dose amount and dosing
Passage of drug across biological membrane Passive diffusion Passive diffusion is a random movement of drug molecules from an area of higher concentration to an area of lower concentration. When a drug is injected into the body, it passively diffuses from the injection site to areas of lower concentration, eventually reaching a blood capillary and entering
Structure of biological membranes in animals Fluid mosaic model Biological membranes may be viewed as mosaics of functional units composed of lipoprotein complex. Most membranes are composed of a fundamental structure called the unit membrane or plasma membrane, that is 80 to 100 Aο thick, surrounds single cells and nuclei. Complex barriers such as the intestinal epithelia and
Route of Drug administration in animals Routes of drug administration can be divided into three main classes as enteral, parenteral and topical. Enteral administration refers to administration of drugs via the gut. Parenteral (par – beyond, enteral – intestinal) administration covers intravenous, intramuscular, subcutaneous, intraperitoneal etc. and Topical application refers to application of drugs on the skin and
