Antibiotics: Bacterial Infections They Effectively Treat

Antibiotics target bacteria—not viruses, fungi, or parasites. Appropriate use requires distinguishing bacterial from non-bacterial etiologies to avoid resistance and adverse effects.

Common Bacterial Infections Treated with Antibiotics

Infection	Typical Pathogens	First-Line Oral Options (Adults)
Strep pharyngitis	GAS (S. pyogenes)	Penicillin V, Amoxicillin
Community-acquired pneumonia	S. pneumoniae, H. influenzae, M. pneumoniae	Amoxicillin, Doxycycline, Macrolide (if atypical)
Acute bacterial sinusitis	S. pneumoniae, H. influenzae, M. catarrhalis	Amoxicillin/clavulanate, Doxycycline
Acute otitis media	S. pneumoniae, H. influenzae, M. catarrhalis	Amoxicillin, Amoxicillin/clavulanate
UTI (cystitis)	E. coli, Klebsiella, Proteus	Nitrofurantoin, TMP-SMX, Fosfomycin
Pyelonephritis	E. coli, Enterobacteriaceae	Ciprofloxacin, TMP-SMX, Ceftriaxone (IV→PO)
Skin/soft tissue (cellulitis)	S. aureus (MSSA/MRSA), Strep	Cephalexin (MSSA), TMP-SMX/Doxy (MRSA)
Gonorrhea	N. gonorrhoeae	Ceftriaxone 500 mg IM + Doxycycline (chlamydia coverage)
Chlamydia	C. trachomatis	Doxycycline, Azithromycin
Bacterial meningitis	S. pneumoniae, N. meningitidis, H. influenzae	Ceftriaxone + Vancomycin ± Ampicillin (empiric IV)
TB (active)	M. tuberculosis	RIPE × 2 mo → RI × 4 mo (directly observed)

Critical Principles

• Culture before antibiotics when feasible (blood, urine, sputum, CSF, wound).
• Narrow spectrum targeted to likely/confirmed pathogen.
• Complete the course as prescribed—duration evidence-based (often shorter than traditional).
• No antibiotics for viral URI, bronchitis, influenza, COVID-19 (unless secondary bacterial infection proven).
• Stewardship: De-escalate based on cultures; avoid fluoroquinolones/3rd-gen cephalosporins when alternatives exist.

Red Flags for Resistance

• Recent hospitalization, antibiotics, travel, healthcare exposure.
• Immunocompromise, indwelling devices.
• Local antibiogram awareness essential.

Antibiotics are precious resources. Prescribe only for confirmed or high-probability bacterial infections.