1 Antibiotics

When antibiotics are appropriate

Antibiotics treat bacterial infections, not viral illnesses. Whether to use one depends on whether treatment is indicated and on the infection, likely or identified organism, susceptibility results, patient-specific factors, and current local guidance.

Antibiotic classes and their targets

Major antibiotic classes target bacterial cell-wall construction, protein synthesis, DNA replication, or folate metabolism. Knowing a class's target helps distinguish it from other classes, but the target alone does not determine the best treatment.

Cell-wall construction

β-lactam antibiotics, including penicillins, bind penicillin-binding proteins and interfere with cell-wall construction. Penicillin or amoxicillin is commonly used for confirmed group A streptococcal pharyngitis when appropriate for the patient.

Vancomycin also interferes with cell-wall synthesis and is used for selected Gram-positive infections. It is not a universal first choice; appropriateness depends on the organism, infection site, susceptibility, and clinical context.

Protein synthesis

Macrolides act at the 50S ribosomal subunit, while tetracyclines act at the 30S subunit. Both classes inhibit bacterial protein synthesis, but their coverage and clinical uses vary by drug and organism, so they are not interchangeable.

DNA replication

Fluoroquinolones such as ciprofloxacin and levofloxacin inhibit bacterial enzymes involved in DNA replication, including DNA gyrase and topoisomerase IV. Whether one is appropriate depends on the infection, susceptibility, and patient-specific risks; broad-spectrum activity alone is not a reason to prefer one.

Folate metabolism

TMP-SMX blocks successive steps in bacterial folate metabolism. It is used for selected susceptible infections, and the diagnosis, likely organism, and susceptibility pattern guide whether it is suitable.

Recognizing when antibiotics are not needed

Routine antibiotics are not recommended for uncomplicated acute bronchitis. Many respiratory illnesses are viral, and antibiotics do not treat viruses. Clinical assessment should consider whether another diagnosis, such as pneumonia, is present.

Colored sputum alone does not establish a reason to start a broad-spectrum antibiotic, and the duration of a cough alone is not an adequate basis for choosing one.

Tailoring treatment to the infection

When culture and susceptibility results are available, reassess treatment using those results alongside the patient's clinical status. Select an effective, appropriately targeted agent rather than continuing an initial broad-spectrum drug regardless of the findings or adding multiple antibiotics simply because a bacterium was identified.

When more than one option is effective, consider infection severity and site, allergies, organ function, adverse-effect risks, and the narrowest suitable spectrum. The newest available drug is not automatically the right choice.

Using antibiotics responsibly

Antibiotic stewardship aims to improve antibiotic use and patient outcomes while reducing avoidable harm and resistance. Use an antibiotic only when indicated, and choose the shortest effective duration supported by guidance.

Selection should follow applicable clinical guidance and take relevant local susceptibility information into account. Fever alone is not a reason to use antibiotics, and broader-spectrum antibiotics do not automatically prevent resistance.