MASTER PHARMACOLOGY NOTES

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 t