Antibiotics
Also known as: antibacterials
Antibiotics are medications that kill bacteria or stop their growth, used to treat bacterial infections. Major classes include penicillins, cephalosporins, macrolides, tetracyclines, fluoroquinolones, and sulfonamides, each attacking a different bacterial target.
Antibiotics are antimicrobial drugs that treat bacterial infections by either killing bacteria (bactericidal agents) or halting their reproduction so the immune system can clear them (bacteriostatic agents). They have no effect on viruses, which is why they are not prescribed for colds or influenza.
Antibiotics are organized into classes by their mechanism of action — the bacterial structure or process they attack. Beta-lactams (penicillins such as amoxicillin, and cephalosporins such as cephalexin) block cell wall synthesis. Macrolides (azithromycin), tetracyclines (doxycycline), and aminoglycosides (gentamicin) inhibit bacterial protein synthesis at the ribosome. Fluoroquinolones (ciprofloxacin) interfere with bacterial DNA replication, and sulfonamides (sulfamethoxazole-trimethoprim) block folate synthesis. Because bacterial targets differ from human cells, these drugs can be selectively toxic to the microbe.
Antibiotics also carry class-specific cautions that pharmacy staff must know: penicillin and sulfa allergies are among the most common drug allergies, tetracyclines should not be taken with dairy or antacids and can discolor developing teeth, and misuse drives antibiotic resistance — the growing problem of bacteria that no longer respond to standard drugs. Counseling patients to complete their prescribed course supports both cure and resistance control.
The PTCE tests antibiotics as a core medication category: recognizing generic and brand names, matching drugs to their classes, and knowing common indications, interactions, and allergy flags. The USMLE Step 1 goes deeper, testing the precise mechanisms of action and the ribosomal targets of protein synthesis inhibitors.
Key takeaways
- Antibiotics treat bacterial infections and are useless against viruses.
- Bactericidal drugs kill bacteria; bacteriostatic drugs stop their growth.
- Major classes are distinguished by target: cell wall (penicillins, cephalosporins), protein synthesis (macrolides, tetracyclines, aminoglycosides), DNA replication (fluoroquinolones), and folate synthesis (sulfonamides).
- Penicillin and sulfa allergies, tetracycline-dairy interactions, and antibiotic resistance are key counseling and safety points.
- The PTCE tests antibiotic names, classes, and indications; the USMLE Step 1 tests their mechanisms in detail.