Pharmocology Flashcards
Define pharmacokinetics
Movement of drugs through the body and their fate
Define pharmodynamics
Effects of a drug on the body and the mechanisms of their actions
What factors affect the rate of absorption?
- Dosage form
- Physical and chemical characteristics of the drug
- Blood flow at the site of administration/absorption
- Route of administration
What are the 2 classes of absorption?
- Enteral: oral, sublingual, rectal
- Parental: intramuscular, intravenous, subcutaneous
What are the characteristics of oral administration?
- Release from dosage form
- The presence of food
- Gastric acid secretion
- Irritation of gastric mucosa
- Microorganisms and gut
How are drugs targeted to specific regions of the body?
- Coating specific to pH of targeted region
- Certain foods must be avoided for the enzyme to not target the food instead of the desired region
True or false: hydrophilic forms are absorbed more rapidly than those in the lipophilic form
True
Are lipophilic forms more readily absorbed oraly?
Yes
What part of the drug is the ionised (charged) portion?
The hydrophilic form
What part of the drug is the non-ionised (uncharged) portion?
The lipophilic form
What factors affect the distribution rate of drugs?
- Regional blood flow
- Lipid solubility of the drug
- Extent of protein binding
- Existence of an active transport system
What functional barriers exist within the body?
- Blood-brain barrier
- Penetration into bone
- Walls of abscesses
- Access to mammary tissue/ prostate tissue/ ocular globe
What are the characteristics of protein binding in relation to drug reactions?
- Blood contains plasma proteins which can bind to specific hormones or compounds used by the body
- The chemical properties of a drug can cause some of the drug to bind to these proteins
- The protein bound portion of the drug is unable to distribute to the tissues
Define diffusion
Movement of molecules from high to low concentration against a concentration gradient
Define facilitated diffusion
Movement of molecules from high to low concentration aided by a carrier
Define active transport
Movement of molecules across the cell membrane from a low to high concentration against a concentration gradient
Define pinocytosis
Cell takes in fluids alongside dissolved small molecules
What are the attributes of drugs undergoung metabolic conversions?
- May reduce the drugs water/fat solubility to increase ease of excretion
- Some drugs need to be metabolised to their active form
What are the sites of drug metabolism?
- Liver (major/main site)
- Kidney
- Lungs
- Plasma
What happens during the phase 1 stage of metabolic reactions?
- Oxidation: loss of electrons
- Reduction: gain of electrons
- Hydrolysis: splitting of drug molecule and addition of water molecule to each portion
What happens during the phase 2 stage of metabolic reactions?
- Involves conjugation
- Chemical groups involved: glucuronic acid, sulphate, methyl. acetyl, glutathiane
- Conjugating enzymes exist in many isoforms and show relative substrate and metabolite specificity
What factors affect drug metabolism?
- Species differences
- Age
- Sex
- Nutrition
- Pregnancy
- Disease
Define clearance
The volume of plasma cleared of drug per unit time
List some examples of how drugs are excreted from the body
- Kidney
- Liver
- Sweat glands
What factors affect excretion?
- Protein binding
- Renal blood flow
- Tubular reabsorption in kidney of lipid-soluble drugs when concentration in tubule rises
What are the stages of hepatic excretion?
- Drug in circulation
- Passive diffusion into the hepatocyte
- Excreted into the bile
- Passes into the GIT
- May undergo enterohepatic circulation
Define half life
Time taken for the drug concentration to be decreased by 50%
What considerations must be taken into account for pharmacodynamics?
- Drug-receptor complexes
- Non-receptor mediated reactions
- Side effects and toxicity
- Drug-drug interactions
- Drug-food interactions
What are the 4 stages of the drug-receptor complex?
A. Active transmembrane ion channels
B. Activate enzymes in the cell
C. Activate internal proteins
D. Activate intracellular receptors: lipid soluble drugs
How do Chelates work being non-receptor-mediated reactions?
- Physically combine with ions/specific compounds to produce their effects
- E.g. EDTA combines with Ca 2+ in blood to prevent clotting mechanism
How do antacid drugs work being non-receptor-mediated reactions?
- Combine with HCl in stomach to form a weaker acid reducing stomach acid
What is the WHO definition to ‘side effects’?
Any response to a drug which is noxious, unintended and occurs at doses used for prophylaxis, diagnosis and therapy
What is a therapeutic index?
The margin of safety which a drug is termed
How is the therapeutic index calculated?
TI= Lethal dose in 50% of animals/Effective dose in 50% of animals
List different common drug side effects
- Gastrointestinal: Nausea, constipation
- Nervous system: seizures, tremors
- Dermatological: Depression, confusion
- Blood disorders: anaemia
What is the classification of Adverse reactions under the Veterinary Medicines Directorate?
A= Enhanced drug effect (predictability, dose dependant, low mortality)
B= Allergic reactions (unpredictable, high mortality)
C= Due to continuous therapy (When patients are on long term therapy)
D= Occurs a long time after treatment (Link to therapy may not be obvious)
E= Occurs on withdrawal of treatment (Often related to sudden drug withdrawal)
What are drug-drug interactions?
- Occurs when the effect of one drug are altered by the effects of another
- Drugs likely to be involved in interactions: highly protein-bound drugs, drugs with low TI
What can have an impact on drug-food interactions?
- Stomach acidity can affect the dissolution and absorption of some drugs
- Drugs requiring an acidic environment for absorption should be given on empty stomach
- Tetracyclines easily bind to Ca2+ ions so absorption is decreased when administered with dairy products or food
List the major drug classes
- Antibiotics
- NSAIDs
- Opioids
- Glucocorticoids
- Anti-emetics
- Analgesics and anaesthetics
