Antibiotic Drug Classes: A Quick PTCB Review Guide
Review the major antibiotic drug classes, mechanisms of action, common examples, and key side effects. Essential pharmacology knowledge for the PTCE exam.
Why Antibiotics Matter on the PTCE
Antibiotics are among the most frequently prescribed medications, making them a high-yield topic on the PTCE. You need to know drug classes, representative examples, major side effects, and important counseling points.
Penicillins
Mechanism: Inhibit bacterial cell wall synthesis. Examples: amoxicillin, amoxicillin-clavulanate (Augmentin), penicillin VK. Key points: Cross-reactivity with cephalosporins in patients with severe penicillin allergy. Amoxicillin is the most commonly prescribed antibiotic in the US. Clavulanate is a beta-lactamase inhibitor that extends amoxicillin's spectrum.
Cephalosporins
Mechanism: Cell wall synthesis inhibition (beta-lactam). Organized by generation (first through fifth). Examples: cephalexin (Keflex) - 1st gen, cefuroxime (Ceftin) - 2nd gen, ceftriaxone (Rocephin) - 3rd gen, cefepime - 4th gen. Each generation expands gram-negative coverage while generally reducing gram-positive activity.
Macrolides
Mechanism: Inhibit protein synthesis by binding the 50S ribosomal subunit. Examples: azithromycin (Zithromax, Z-pack), clarithromycin (Biaxin), erythromycin. Key side effects: GI upset, QT prolongation. Azithromycin has significant drug interactions with warfarin and statins.
Fluoroquinolones
Mechanism: Inhibit DNA gyrase and topoisomerase IV. Examples: ciprofloxacin (Cipro), levofloxacin (Levaquin), moxifloxacin (Avelox). Black box warnings: tendon rupture, peripheral neuropathy, CNS effects. Avoid with dairy, antacids, and iron (chelation reduces absorption).
Tetracyclines
Mechanism: Inhibit protein synthesis at the 30S ribosomal subunit. Examples: doxycycline, minocycline, tetracycline. Key counseling: Avoid dairy, antacids, and sun exposure. Do not use in children under 8 or pregnant women (tooth discoloration).
Sulfonamides
Example: Sulfamethoxazole-trimethoprim (Bactrim). Mechanism: Inhibits folate synthesis. Watch for sulfa allergies, photosensitivity, and hyperkalemia. Significant warfarin interaction.
Use PTCB flashcards to drill antibiotic classes and their unique counseling points.
Ready to ace the PTCE?
Practice with 800+ flashcards, 40 mini exams, and 10 full-length PTCE simulations.
Start Free