- Likely Organisms: S. pneumoniae, M. pneumoniae, C. pneumoniae, H. influenzae, respiratory viruses.
- Healthy Adult (No comorbidities):
- 1st Line: Amoxicillin 1g TID or Doxycycline 100mg BID.
- An alternative is a macrolide like Azithromycin or Clarithromycin, but only if local pneumococcal resistance is <25%.
- Adult with Comorbidities (e.g., chronic heart, lung, liver, or renal disease; DM; alcoholism; malignancy):
- Combination Therapy: Amoxicillin/clavulanate OR a cephalosporin (e.g., cefpodoxime, cefuroxime) PLUS a macrolide (e.g., azithromycin) or doxycycline.
- Monotherapy: Respiratory fluoroquinolone (e.g., Levofloxacin, Moxifloxacin).
- Duration: Minimum of 5 days, and until patient is clinically stable.
Skin and Soft Tissue Infection (SSTI)
- Non-purulent (Cellulitis/Erysipelas):
- Likely Organisms: Streptococcus pyogenes, some S. aureus.
- 1st Line: Cephalexin, Dicloxacillin, or Flucloxacillin. For penicillin allergy, Clindamycin is an alternative.
- Purulent (Abscess/Furuncle):
- Likely Organisms: S. aureus (including MRSA).
- Tx: Incision & Drainage (I&D) is primary. Antibiotics are for systemic signs or severe infection.
- 1st Line (MRSA coverage): Doxycycline, Trimethoprim-sulfamethoxazole (TMP-SMX).
Urinary Tract Infections (UTI)
- Uncomplicated Cystitis (Bladder):
- Likely Organism: E. coli.
- 1st Line: Nitrofurantoin (5 days), TMP-SMX (3 days, if local resistance <20%), or Fosfomycin (single dose).
- Fluoroquinolones are generally reserved for when other options cannot be used.
- Pyelonephritis (Kidney Infection) - Outpatient:
- Likely Organism: E. coli.
- 1st Line: Fluoroquinolones (e.g., Ciprofloxacin, Levofloxacin) if local resistance is low.
- Alternatives include TMP-SMX or a beta-lactam after an initial IV dose of ceftriaxone.
- Note: Nitrofurantoin and fosfomycin do not achieve adequate kidney tissue levels and should not be used for pyelonephritis.
Upper Respiratory Infections
- Strep Pharyngitis (Strep Throat):
- Likely Organism: Group A Streptococcus (S. pyogenes).
- 1st Line: Penicillin V or Amoxicillin for 10 days.
- For Penicillin allergy: 1st-generation cephalosporin (e.g., Cephalexin), Clindamycin, or a macrolide (e.g., Azithromycin).
- Acute Otitis Media (AOM):
- Likely Organisms: S. pneumoniae, H. influenzae, M. catarrhalis.
- 1st Line: High-dose Amoxicillin (80-90 mg/kg/day).
- For treatment failure or recent amoxicillin use: Amoxicillin-clavulanate.
Bacterial Meningitis (Empiric Therapy by Age)
- Neonate (<1 month): Ampicillin (for Listeria) + Gentamicin OR Cefotaxime (for E. coli, GBS).
- 1 month - 50 years: Ceftriaxone + Vancomycin (for resistant S. pneumoniae).
- >50 years or Immunocompromised: Ceftriaxone + Vancomycin + Ampicillin (to cover Listeria).
Sexually Transmitted Infections (STIs)
- Gonorrhea (Uncomplicated):
- 1st Line: Ceftriaxone 500 mg IM (single dose).
- Chlamydia (Uncomplicated):
- 1st Line: Doxycycline 100 mg BID for 7 days.
- Alternative: Azithromycin 1g (single dose).
- Syphilis:
- 1st Line: Benzathine Penicillin G IM. Dosing depends on the stage of syphilis.
Other Key Infections
- Clostridioides difficile Infection (CDI):
- 1st Line (Initial Episode): Oral Fidaxomicin or oral Vancomycin. Metronidazole is no longer recommended as first-line therapy for adults.
- Surgical Prophylaxis:
- 1st Line: Cefazolin (Ancef) given within 60 minutes before incision.
- For beta-lactam allergy: Vancomycin or Clindamycin.
- For colorectal surgery: Add Metronidazole for anaerobic coverage.