Pharmacology
Antibiotics
Antibiotics are antibacterial medicines that target essential structures or processes within bacteria. Grouping them by their main mechanism of action makes their spectrum, clinical uses, adverse effects and resistance patterns far easier to learn.
19 classes across 6 mechanism families.
1. Cell wall synthesis inhibitors
These antibiotics interfere with bacterial cell-wall formation, weakening susceptible bacteria and ultimately causing cell death or inhibition of growth.
- Penicillins — β-lactams that bind penicillin-binding proteins; spectrum differs sharply by subclass.
- Cephalosporins — β-lactams conventionally grouped into generations with broadly shifting spectrum.
- Carbapenems — Very broad-spectrum β-lactams reserved for serious or resistant infections.
- Monobactams — A monocyclic β-lactam class represented in practice by aztreonam.
- Glycopeptides — Non-β-lactam cell-wall inhibitors active against Gram-positive organisms including MRSA.
2. Protein synthesis inhibitors
These antibiotics bind bacterial ribosomal subunits and prevent production of the proteins required for bacterial growth and survival.
- Aminoglycosides — 30S-binding bactericidal agents with important toxicity monitoring.
- Tetracyclines — 30S-binding bacteriostatic agents with broad atypical coverage.
- Macrolides — 50S-binding agents widely used in respiratory and atypical infections.
- Lincosamides — 50S-binding agents with anaerobic and Gram-positive activity.
- Oxazolidinones — 50S-binding agents active against resistant Gram-positive organisms.
3. Nucleic acid synthesis inhibitors
These drugs interfere with bacterial DNA replication or RNA synthesis.
- Fluoroquinolones — DNA gyrase and topoisomerase IV inhibitors with significant safety warnings.
- Rifamycins — RNA polymerase inhibitors central to antimycobacterial therapy.
4. Folate synthesis inhibitors
These drugs interrupt bacterial folate metabolism, a pathway required for the synthesis of nucleic acids.
- Sulfonamides — Dihydropteroate synthase inhibitors, usually combined with trimethoprim.
- Trimethoprim — Dihydrofolate reductase inhibitor used alone or with sulfamethoxazole.
5. Cell membrane–active antibiotics
These agents disrupt the bacterial cell membrane and interfere with membrane integrity.
- Polymyxins — Last-resort agents against multidrug-resistant Gram-negative organisms.
- Daptomycin — Lipopeptide active against Gram-positive organisms, inactivated by surfactant.
6. Other important antibacterial agents
These clinically important antibacterial drugs have mechanisms that are best studied separately.
- Metronidazole — Nitroimidazole active against anaerobes and several protozoa.
- Fosfomycin — Single-dose oral option for selected uncomplicated urinary infections.
- Mupirocin — Topical agent used for selected skin and nasal staphylococcal indications.
Studying this the efficient way
Learn the mechanism family first, then the classes inside it. Almost every exam question about spectrum, adverse effects or resistance is really a question about which mechanism a drug belongs to. Each class page ends with a 60-second revision block and the traps students most often fall for.