🧠 The theory: the right drug, dose and duration
An antibiotic must reach the site of infection at a high enough concentration to kill or stop the likely organism, without causing unnecessary harm or driving resistance. That balance drives every decision: a narrow-spectrum drug when the organism is known, a broad-spectrum drug only when it must cover uncertainty, the correct dose and route, and the shortest course that works. Overuse selects for resistant bacteria and increases the risk of Clostridioides difficile.
Key concepts
- •Spectrum: narrow-spectrum antibiotics target fewer organisms; broad-spectrum cover many but disturb normal flora more and encourage resistance.
- •Empirical therapy is a best guess before culture results; targeted therapy is guided by sensitivities, allowing de-escalation to a narrower drug.
- •Bactericidal drugs kill bacteria; bacteriostatic drugs stop them multiplying.
- •Review at 48 to 72 hours, and switch from intravenous to oral when the patient improves.
Antimicrobial stewardship
📌 Stewardship aims to
- •Use antibiotics only when needed (most coughs, colds and sore throats are viral).
- •Choose the right drug, dose, route and duration, following local antimicrobial policy.
- •Slow the development of resistance and reduce side effects and C. difficile infection.
- •Document the indication and a review or stop date.
Assessing penicillin allergy
Many patients labelled penicillin-allergic have had a non-allergic reaction such as nausea. Clarify the nature of the reaction: a mild rash is different from anaphylaxis (swelling, wheeze, collapse). A true, severe penicillin allergy rules out penicillins and, for the most severe reactions, cephalosporins, so accurate allergy history matters.
⚠️ Do not use antibiotics for viral illness
The commonest exam trap is offering an antibiotic for a self-limiting viral illness. Antibiotics do not help colds, most sore throats or viral coughs, and unnecessary use drives resistance and side effects.
Test yourself
What is the difference between empirical and targeted antibiotic therapy?
Answer: Empirical therapy is a best guess before culture results; targeted therapy is guided by sensitivities, allowing a switch to a narrower-spectrum drug.
Give two aims of antimicrobial stewardship.
Answer: Using antibiotics only when needed, choosing the right drug and duration, slowing resistance, and reducing side effects and C. difficile (any two).