Summary Complete CAT Prep — Wednesday to Sunday Key Points - ### Complete CAT Prep — Wednesday to Sunday - ## WEDNESDAY ## Principles of Rational Antimicrobial
Summary Complete CAT Prep — Wednesday to Sunday Key Points - Complete CAT Prep — Wednesday to Sunday - WEDNESDAY Principles of Rational Antimicrobial Prescribing & Infectious Diseases - What is an Antimicrobial Drug? - An antimicrobial is any drug that fights microorganisms — tiny living things that cause disease. - There are four types of microorganisms and a specific drug class for each: - - Bacteria → treated with Antibiotics - Viruses → treated with Antivirals - Fungi → treated with Antifungals - Parasites → treated with Antiparasitics - The word antimicrobial covers all of these. - In this course, most of the focus is on antibiotics. Detailed Notes --- WEDNESDAY Principles of Rational Antimicrobial Prescribing & Infectious Diseases --- What is an Antimicrobial Drug? An antimicrobial is any drug that fights microorganisms — tiny living things that cause disease. There are four types of microorganisms and a specific drug class for each: - Bacteria → treated with Antibiotics - Viruses → treated with Antivirals - Fungi → treated with Antifungals - Parasites → treated with Antiparasitics The word antimicrobial covers all of these. In this course, most of the focus is on antibiotics. --- Rational Prescribing — What Does it Mean? Rational prescribing means giving the correct drug, to the correct patient, at the correct dose, for the correct duration, and only when it is truly needed. You do not give antibiotics randomly. You think before you prescribe. Wrong prescribing causes treatment failure, side effects, and drug resistance. --- How Does the Body Signal an Infection? When bacteria or other organisms enter the body, the immune system responds with inflammation . The classic signs of inflammation are: - Fever - Redness - Swelling - Pain - Loss of function in the affected area The location of these signs tells you where the infection is. Different body sites show different signs: Site of Infection Key Signs and Symptoms ------------------ ---------------------- Brain and spinal cord (CNS) Severe headache, stiff neck, sensitivity to light, high fever, confusion Lungs Cough, difficulty breathing, chest pain, fever, sputum production Urinary tract Burning when urinating, frequent urination, cloudy urine, flank pain (kidney involvement) Skin Redness, warmth, swelling, pus, open sores Gut Diarrhea, vomiting, abdominal pain, fever --- Host Factors — The Patient Affects Drug Choice Before prescribing, you must think about the patient. These patient-specific things are called host factors: - Age — newborns and elderly have weaker immune systems. Some drugs harm children e.g. Tetracycline damages developing teeth and bones - Pregnancy — some drugs cross to the baby and cause harm. Avoid Tetracyclines and Fluoroquinolones in pregnancy. Safe options include Amoxicillin and Cephalexin - Kidney function — most drugs leave the body through the kidneys. Poor kidney function means drug builds up and becomes toxic. Dose must be reduced - Liver function — the liver breaks down many drugs. Liver disease means the drug stays in the body too long. Adjust dose accordingly - Allergies — if a patient is allergic to Penicillin, avoid all Penicillin-type drugs. Use a Macrolide (e.g. Azithromycin) instead - Immune status — a patient with HIV or on chemotherapy has a weak immune system and needs stronger, broader antimicrobial cover --- Empirical Therapy vs Definitive Therapy This is one of the most tested concepts. Understand it clearly. Empirical therapy means you start treatment before you even know exactly which organism is causing the infection. You make an educated guess based on the site of infection and the most likely organisms that infect that site. You start treatment immediately because waiting for lab results can cost the patient's life. Definitive therapy means you now have the lab results. You know exactly which organism is causing the infection and which drug kills it. You then adjust the treatment to target that specific organism. This is called de-escalation — narrowing from a broad drug to a more specific one. In short: - Empirical = treat first, based on best guess - Definitive = treat after lab confirms the organism - Always de-escalate once lab results return --- Isolating an Organism — How the Lab Confirms Infection To find out exactly what is causing the infection, you collect a sample from the patient. This is called a specimen . Common specimens include: - Blood - Urine - Sputum (mucus coughed up from lungs) - Wound swab - CSF (cerebrospinal fluid — fluid around the brain, collected by lumbar puncture) The specimen is sent to the lab where they: 1. Grow the organism in a dish — this is called culturing 2. Identify the organism 3. Test which antibiotics kill it — this is called sensitivity testing The final result is called a Culture and Sensitivity (C&S) report. It tells you exactly which drug to use. --- Antimicrobial Dosing Getting the dose right is critical. Too little and the drug does not work. Too much and it becomes toxic. - Loading dose — a high first dose given to quickly get the drug to a therapeutic level in the blood. Used when you need the drug to work fast - Maintenance dose — the regular dose given after the loading dose to keep the drug at the right level - MIC (Minimum Inhibitory Concentration) — the lowest concentration of a drug that stops bacteria from growing. The drug level in the body must stay above the MIC to be effective Dosing is also affected by: - How severe the infection is - Where the infection is (some drugs do not penetrate certain sites well, e.g. the brain) - The patient's kidney and liver function - Body weight --- Treatment Failure — Why Does it Happen? Sometimes a patient does not get better despite being on antibiotics. This is called treatment failure. Reasons include: - Wrong drug chosen — the organism is resistant to it - Wrong dose — too low to kill the bacteria - Too short a duration — stopped before all bacteria were killed - Patient did not take the medication as prescribed (poor adherence) - The drug is not reaching the infection site e.g. some antibiotics do not penetrate the brain well - The patient's immune system is too weak to assist the drug - The patient has been reinfected --- Antimicrobial Toxicity — Side Effects of Key Drugs Every drug has side effects. These are the most important ones to know: Drug Major Side Effect ------ ------------------ Aminoglycosides (e.g. Gentamicin) Kidney damage (nephrotoxicity) and hearing damage (ototoxicity) Tetracyclines (e.g. Doxycycline) Damages teeth and bones in children. Avoid in pregnancy and children under 8 Chloramphenicol Aplastic anaemia (bone marrow stops making blood cells). In newborns — Gray Baby Syndrome (baby turns grey, collapses) Fluoroquinolones (e.g. Ciprofloxacin) Tendon damage (especially Achilles tendon rupture). Prolonged QT interval (heart rhythm problem) Metronidazole Metallic taste in mouth, peripheral neuropathy (nerve damage in hands and feet). Never take with alcohol — causes severe vomiting Sulfonamides (e.g. Cotrimoxazole) Stevens-Johnson Syndrome (severe, life-threatening skin reaction). Crystalluria (drug crystals form in urine and damage kidneys) --- Antimicrobial Resistance (AMR) — A Major Global Problem AMR means bacteria have changed in a way that makes them no longer killed by a drug that used to work. This is a major global health crisis. How does resistance happen? Bacteria are very adaptable. When exposed to antibiotics repeatedly or incorrectly, they develop strategies to survive: - Beta-lactamase production — bacteria produce an enzyme that breaks down Penicillin-type drugs before the drug can work. This is the most common resistance mechanism - Altered drug target — the bacteria change the structure that the drug normally binds to, so the drug cannot attach - Efflux pumps — bacteria develop pumps that push the antibiotic out of the bacterial cell before it can cause damage - Reduced permeability — bacteria change thei