Revision Questions Flashcards
Please explain the effects of a receptor mediated and non receptor mediated drug within the body
The drug is known as an AGONIST (or receptor mediated) as it mimics the action of the body’s own chemicals at appropriate receptor sites.
A Non receptor mediated drug (antagonist) combines with receptor sites, but fails to initiate a response.
Please explain how a drug is distributed to its destination site
After a drug is absorbed it passes through various body fluids. It passes to the blood plasma, into interstitial fluid where some molecules attach to the cell membrane, trans-cellular fluid and then into the intracellular fluid
Please explain how amoxicillin is metabolised by the liver.
The liver produces enzymes that transform drugs into water-soluble metabolites that can be passed in the urine. Some highly lipid soluble drugs are incorporated into bile and eliminated via the biliary system.
Biotransformation (metabolism) usually occurs in two phases:
Phase 1: The original molecule is transformed by a process of oxidation,
reduction or hydrolysis.
Phase 2: The enzymes, conjugate the phase 1 metabolite with another molecule e.g. glucuronic acid, sulphate or glycine to produce a hydrophilic molecule.
The liver excretes drugs by first incorporating them into the bile, which is then passed into the small intestine. Once it reaches the small intestine, it will either be passed in the faeces or in some cases it can be reabsorbed into the blood stream.
Why is aspirin so toxic to cats?
Cats have a decreased ability to metabolise drugs like aspirin as they have a reduced ability to form glucuronic acid. This is why it is so toxic to cats.
Explain the role of the kidney in the process of metabolism and excretion of Frusemide.
Frusemide is a loop diuretic and exerts its effect on the Loop of Henle in the kidney. It causes diuresis by inhibiting the re-absorption of sodium from the Loop of Henle. As sodium is retained in the urine, water is also retained. At the level of the distal convoluted tubule potassium is exchanged for sodium so some sodium is absorbed back into the body while potassium is excreted. Because osmotic pressure of urine stays the same, the water stays in the urine and is excreted from the body along with the potassium. It works by decreasing oedema.
There are two ways in which the kidneys excrete drugs:
Glomerular filtration: The glomerulus in the kidney filters drug molecules out of the blood into the glomerular filtrate, which is then eliminated as urine.
Tubular secretion: The kidney tubule cells secrete metabolites out of the capillaries surrounding the tubule and into the glomerular filtrate, which then becomes urine.
There are two ways in which the kidneys excrete drugs:
Glomerular filtration: The glomerulus in the kidney, filters drug molecules out of the blood into the glomerular filtrate, which is then eliminated as urine.
Tubular secretion: The kidney tubule cells secrete metabolites out of the capillaries surrounding the tubule and into the glomerular filtrate, which then becomes urine.
Describe how phenobarbital acts on the body in the case of epilepsy.
It acts by decreasing the spontaneous depolarisation of brain cells or preventing the spread of depolarisation resulting in a milder fit than would normally occur without the treatment.
Please describe the formulation of a capsule.
Contain granules or powders contained in a hard outer case made of gelatine. The case comes in two halves that slot together. Some have different size granules so they can dissolve at different rates
What precautions should be taken when handling and administering a cytotoxic drug?
Preparing and administering the drug in a well ventilated area away from human traffic
Wearing protective clothing ie: goggles, high efficiency filter mask, a non porous long sleeve gown with tight cuffs and a double pair of latex gloves.
Pregnant women must not handle cytotoxic drugs.
Please explain the mode of action of meloxicam.
Meloxicam is a non steroidal anti inflammatory drug for use in dogs. It is used to alleviate inflammation and pain in both acute and chronic musculo-skeletal disorders
Please explain the mode of action of amoxicillin.
It is a broad spectrum antimicrobial drug which is bacteriocidal in action, which means that it kills the bacteria. The mode of action is that they prevent cross-linking of bacterial cell walls.
Explain how a dead (killed) vaccine elicits a response in the animals body.
The organisms are unable to reproduce and are therefore incapable of
causing disease. They provide a weak immune response of shorter duration
and often require large doses to give protection.
Describe the characteristics of ivermectin.
Ivermectin acts by enhancing the actions of certain compounds in the body, which inhibits nervous transmission.
NOTE: Ivermectin can produce adverse reactions in collies and collie cross dogs. Can be fatal.
Please explain the terms bacteriocidal and bacteriostatic.
Bacteriocidal means that the drug kills the bacteria and bacteriostatic means that it stops the bacteria from multiplying.
Describe the two ways in which an orally administered drug reaches the site of action.
Selective: Substances, which the body particularly wants, for example amino acids, are carried across the membrane by an energy consuming mechanism. This can occur against a concentration gradient i.e. from an area of low concentration of substance within the bowel to an area of high concentration within the cells. Some drugs, because of their resemblance to naturally occurring substances, use these existing transport mechanisms.
Non Selective: The substances pass through the membrane from an area of high concentration within the bowel to an area of low concentration within the cells.
Please describe 6 factors that affect absorption of a drug.
Chemical nature: The acid in the stomach breaks down some drugs, whilst intestinal enzymes digest others. Such drugs can only be given by injection.
Solubility: Drugs given in solution are more rapidly absorbed than those in solid forms. Also local conditions at the site of absorption can alter drug solubility. For example, stomach acid can cause precipitation of the drug, which will slow the rate of absorption.
Concentration: High concentrations of drugs are absorbed more rapidly than low concentrations.
Bowel Movement: Most drugs are absorbed from the upper part of the small intestine and alteration of the gut motility can influence drug absorption e.g. diarrhoea.
Food: Dilution of the drug by food and drink can lead to slowing of absorption.
Formulation: A liquid will be more rapidly absorbed than a solid medicine
