Antibiotic Coverage Cheat Sheet for Exams

Antibiotic coverage questions ask you to choose the right drug for the likely organism. Learning every antibiotic individually is difficult, so group them by class and remember the highlights. This cheat sheet is a starting point to be combined with practice questions.

Beta-lactams

• Penicillin: streptococci and Treponema
• Amoxicillin: broader, with some Gram-negative and Listeria cover
• Anti-staphylococcal penicillins: methicillin-sensitive Staphylococcus aureus
• Piperacillin-tazobactam: very broad, including Pseudomonas and anaerobes
• Cephalosporins: first generation for Gram-positive skin infections and surgical prophylaxis, third generation such as ceftriaxone for meningitis and many Gram-negative infections, and ceftazidime for Pseudomonas
• Carbapenems: very broad, but not for methicillin-resistant Staphylococcus aureus or atypical organisms

Check for allergy and cross-reactivity.

Other major classes

• Vancomycin: Gram-positive cover including methicillin-resistant Staphylococcus aureus, with kidney and infusion reaction risks
• Aminoglycosides: Gram-negative cover, no anaerobic activity, with kidney and ear toxicity
• Macrolides: atypical organisms and streptococci, with QT and interaction issues
• Fluoroquinolones: respiratory and urinary infections, with tendon, QT and cartilage concerns
• Doxycycline: atypical organisms and rickettsial infections, avoided in pregnancy and young children
• Metronidazole: anaerobes and protozoa, avoid alcohol
• Clindamycin: anaerobic and Gram-positive cover, with a risk of Clostridioides difficile infection
• Trimethoprim-sulfamethoxazole: urinary infection and Pneumocystis, with hyperkalemia and allergy risks
• Nitrofurantoin: lower urinary infection, avoided in significant kidney impairment
• Linezolid: resistant Gram-positive organisms, with a risk of serotonin syndrome

Quick rules

• No aminoglycosides for anaerobes
• Ceftriaxone does not cover Listeria
• Choose the narrowest effective drug once culture results are available
• Adjust doses in kidney and liver disease
• Check pregnancy and breastfeeding safety

Think by syndrome

Match the drug to the infection site. For example, community-acquired pneumonia needs coverage for pneumococcus and, in many cases, atypical organisms. A urinary infection needs coverage for Escherichia coli. Meningitis needs a drug that crosses the blood-brain barrier.

A classic exam pattern

A patient with a penicillin allergy and a skin infection with suspected methicillin-resistant Staphylococcus aureus may need a drug with specific cover, such as vancomycin or another agent according to local guidance.

Study tips

• Build a one-page table for class, spectrum and cautions
• Always connect drug choice to organism and site
• Review each wrong answer for the gap in your spectrum knowledge

This article is for exam revision and does not replace current clinical guidelines. Practice with the Namazj free trial.