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Case 0: Foundation - Coggle Diagram
Case 0: Foundation
Mode of transmission of Infectious agents
Describe the routes of transmission and how infectious agents are spread.
The chain of infection
Infectious agent
Reservoir
Portal of exit
Mode of transmission
Portal of entry
Susceptible host
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How the micro-organism enters a new host
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How the pathogen moves from one host to another
Direct
- When an infectious agent is transferred immediately from a host to another without a long-term intermediate
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Indirect
- When an infectious agent is transferred from one person to another through an intermediate object, surface, or organism
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How the micro-organism leaves the body
Resp. secretions, blood, urine, feces, saliva. open wounds
Where the micro-organism survives
Humans, animals, soil, water, contaminated surfaces
The micro-organism that causes the disease
Bacteria, viruses, fungi, etc.
Describe the principles of infection control
Standard precautions
It is the basic level of precaution that is essential to provide a high level to patients, healthcare workers and visitors
Hand washing and antisepsis
Use of personal protective equipment when handling blood, body substances, excretions and secretions;
Appropriate handling of patient care equipment and soiled linen
Prevention of needlestick/sharp injuries
Environmental cleaning and spills-management
Appropriate handling of waste.
Additional precautions
Drug Absorption & Distribution
Explain the differences between various routes of drug administration
Oral:
Absorbed through the GI tract
Convenient and non-invasive
First-pass metabolism reduces bioavailability
Parenteral
Intravenous (IV):
Directly injection into the bloodstream
100% bioavailability
Rapid onset
Intramuscular (IM):
Injected into muscles
Moderate absorption and sustained release of drug
Subcutaneous (SC):
Injected uner the skin
Slow, steady absorption
Inhalation:
Drug is inhaled into the lungs
Rapid absorption into pulmonary circulation
Topical:
Applied directly to the skin for local effects
Sublingual:
Placed under the tongue or against the cheek
Bypasses first pass metabolism
Rectal:
Administerd via the rectum
Useful for unconscious or vomiting patients
Partially bypasses first-pass metabolism
Describe how one drug can influence the absorption of another
Factors affecting GI absorption:
Particle size and formulation
Gut motility and surface area
More gut movement, less absorption
Gut pH:
Some drugs are absorbed better in acidic or alkali conditions
Strong acid or strong basic conditions can lead to poor absorption
Other drugs can change GI pH, or gut motility
Physio-chemical interaction
Interactions with food and/or other drugs
Other drugs form chelations, or conjugates, reducing absorption
Competition for carriers/transporters
Drugs that are carried by a certain transporter will compete with other drugs carried by the same transporter
Describe how the physical chemical characteristics of drugs influence their movement across physiological barriers
Drug movement across physiological barriers depends on:
Lipid solubility
Molecular size
Ionization
Protein binding
Presence of Transporters
Lipid solubility:
Lipophilic drugs:
Easily cross lipid membranes via passive diffusion
Typically have a larger Volume of distributions allowing them to reach intracellular targets
Hydrophilic drugs:
Require transport proteins for membrane passage
Mostly confined to plasma and ECF
Ionization:
Drugs exist in ionized and unionized forms
Only unionized forms can passively diffuse across membranes
The ionization state of a drug depends on the
pKa of the drug
, and the
pH of the environment of the drugs location
pKa = pH at which 50% of a drug is ionized and 50% remains unionized in a solution
Represents the strength of an acid of base in a given environment
Weak acids are absorbed well in acidic environments like the stomach
Weak bases are absorbed well in alkali environments such as the intestines
Ion trapping:
Acidic drugs become more ionized in alkaline environments
Basic drugs become more ionized in acidic environments
When these drugs are ionized, they cannot diffuse back across the membrane, causing them to be trapped
Explain the distribution of drugs across body compartments
Factors affecting drug distribution:
Membrane permeability
Blood perfusion
Lipid solubility
pH-pKa
Plasma protein binding
Tissue binding
Plasma protein binding:
Drugs can reversibly bind to plasma proteins in the blood
Some drugs are plasma protein bound, others are not
Drugs that are plasma protein bound:
Shows slower acting and prolonged therapeutic effects since the drug is not cleared as easily
Drugs that are not plasma protein bound:
Faster acting, but shorter therapeutic effects, cleared faster
Tissue binding:
Drugs with a high Vd are extensively stored within specific cells or tissues (>40L)
Drugs with a moderate Vd distributes in ECF (5-15L)
Drugs with a low Vd remains mostly in plasma (<5L)
A loading dose is given to rapidly achieve a therapeutic drug concentration in the body. Typically used for high Vd drugs where more drug is needed to saturate tissue stores quickly
Membrane permeability:
Drugs perfuse faster through highly permeable membranes
Blood perfusion:
Drugs reach highly vascularised tissues faster
Volume of distribution = Dose administered / plasma concentration
Drug metabolism and Excretion
Define bioavailability
The proportion of a drug that passes into systemic circulation after admninstration
Is dependent of Absorption and Metabolism
Describe first pass metabolism and its importance
Drug metabolism occuring during its passage from the site of absorption into systemic circulation
Results in a great decrease in bioavailability of a drug, which leads to a great decrease in therapeutic response
Can be bypassed by choosing sublingual, transdermal, or parenteral route of administration
Define phase I and II metabolism
Phase 1 metabolism:
Introduces or unmasks a functional group in the drug molecule
Metabolite may be active or inactive, lipid soluble or water soluble
The enzymes are mainly microsomal, except a few which are non-microsomal
Microsomal enzymes - Enzymes found primarily in the Smooth ER of cells in the body, which are involved in drug metabolsim.
Phase 2 metabolism:
An endogenous radical is conjugated to the drug
Metabolite is usually polar, water soluble, and is mostly inactive
Catalyzed by microsomal and non-microsomal mitochondrial or cytoplasmic enzymes
Results in a larger, more water-soluble compound that is easier for the body to excrete
Explain the role of the liver and cytochromes in drug metabolism and clearance
Explain the routes of drug excretion from the body
