What are examples of antibiotics, their coverage, side effects, and dosages in both oral and intravenous (IV) forms?

Antibiotics: Examples, Coverage, Side Effects, and Dosages

Antibiotics should be selected based on the suspected pathogen, infection site, local resistance patterns, and patient factors, with a preference for the narrowest spectrum agent effective against the suspected pathogen to minimize resistance development and adverse effects.

Common Antibiotic Classes and Examples

Penicillins

• Amoxicillin

  • Coverage: Gram-positive cocci (except MRSA), some Gram-negative bacilli
  • Dosage: 500 mg PO q8h or 875 mg PO q12h
  • Side effects: Rash, diarrhea, hypersensitivity reactions

• Amoxicillin-Clavulanate

  • Coverage: Extended to include beta-lactamase producing organisms
  • Dosage: 875/125 mg PO q12h or 500/125 mg PO q8h; 1.2 g IV q8h 1
  • Side effects: Diarrhea, nausea, rash, elevated liver enzymes

• Oxacillin/Nafcillin

  • Coverage: MSSA infections
  • Dosage: 2 g IV q4-6h 2
  • Side effects: Phlebitis, neutropenia, hepatotoxicity

Cephalosporins

First Generation

• Cefazolin

  • Coverage: MSSA, streptococci, some Gram-negative bacilli
  • Dosage: 2 g IV q8h 2
  • Side effects: Hypersensitivity, seizures at high doses

• Cephalexin

  • Coverage: Similar to cefazolin but oral
  • Dosage: 500 mg PO q6h 2
  • Side effects: Diarrhea, nausea, rash

Third Generation

• Ceftriaxone
  • Coverage: Broad Gram-negative coverage, streptococci, some anaerobes
  • Dosage: 1-2 g IV q24h 1
  • Side effects: Gallbladder sludging, hemolytic anemia, diarrhea

Fluoroquinolones

• Levofloxacin

  • Coverage: Gram-positive (including S. pneumoniae), Gram-negative, atypical pathogens 3
  • Dosage: 750 mg PO/IV q24h for 5-14 days (respiratory); 250-500 mg PO/IV q24h for UTIs 2, 4
  • Side effects: Tendinitis/tendon rupture, QT prolongation, CNS effects, photosensitivity 3

• Ciprofloxacin

  • Coverage: Excellent Gram-negative coverage including Pseudomonas
  • Dosage: 400 mg IV q12h or 500-750 mg PO q12h 2
  • Side effects: Similar to levofloxacin

Macrolides

• Azithromycin
  • Coverage: Atypical pathogens, streptococci, some Gram-negative organisms
  • Dosage: 500 mg PO day 1, then 250 mg PO daily for 4 days; or 500 mg PO daily for 3 days 5, 2
  • Side effects: QT prolongation, GI upset, hepatotoxicity

Tetracyclines

• Doxycycline
  • Coverage: Broad spectrum including atypical pathogens and MRSA
  • Dosage: 100 mg PO/IV q12h 1
  • Side effects: Photosensitivity, GI upset, tooth discoloration in children

Glycopeptides

• Vancomycin
  • Coverage: Gram-positive organisms including MRSA
  • Dosage: 15-20 mg/kg IV q8-12h 2
  • Side effects: Red man syndrome, nephrotoxicity, ototoxicity

Lincosamides

• Clindamycin
  • Coverage: Gram-positive cocci, anaerobes
  • Dosage: 600 mg IV/PO q8h 2
  • Side effects: C. difficile colitis, rash, metallic taste

Oxazolidinones

• Linezolid
  • Coverage: MRSA, VRE, resistant pneumococci
  • Dosage: 600 mg PO/IV q12h 2
  • Side effects: Myelosuppression, peripheral neuropathy, serotonin syndrome

Antibiotic Selection by Infection Type

Skin and Soft Tissue Infections

1. Impetigo/Cellulitis:

   • First-line: Dicloxacillin, cephalexin, amoxicillin-clavulanate 2
   • MRSA suspected: TMP-SMX, doxycycline, or linezolid 2

2. Necrotizing Fasciitis:

   • Combination therapy: Vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem 2

3. Surgical Site Infections:

   • Trunk/extremity: Oxacillin, nafcillin, cefazolin, cephalexin 2
   • Intestinal/genitourinary: Piperacillin-tazobactam, ertapenem, or ceftriaxone plus metronidazole 2

Respiratory Infections

1. Community-Acquired Pneumonia:

   • Outpatient: Amoxicillin or doxycycline or azithromycin
   • Inpatient: Levofloxacin 750 mg daily or ceftriaxone plus azithromycin 2, 6

2. Hospital-Acquired Pneumonia:

   • Anti-pseudomonal β-lactam plus aminoglycoside or fluoroquinolone 2

3. Atypical Pneumonia:

   • Mycoplasma/Chlamydophila: Doxycycline 100 mg bid or azithromycin 500 mg day 1, then 250 mg daily 2
   • Legionella: Levofloxacin 750 mg daily or azithromycin 2

Genitourinary Infections

1. Uncomplicated UTI:

   • First-line: TMP-SMX, nitrofurantoin
   • Alternative: Fluoroquinolones (levofloxacin 250-500 mg daily) 3

2. Sexually Transmitted Infections:

   • Gonorrhea: Ceftriaxone 250 mg IM single dose 2
   • Chlamydia: Azithromycin 1 g PO single dose or doxycycline 100 mg bid for 7 days 2

Special Considerations

Pediatric Patients

• Avoid tetracyclines in children <8 years (dental staining) 1
• Avoid fluoroquinolones in children <18 years (cartilage toxicity) 1
• Dosing: Generally weight-based (mg/kg)

Pregnancy

• Avoid tetracyclines (teratogenic) 1
• Avoid fluoroquinolones (potential teratogenicity) 1
• Preferred: Penicillins, cephalosporins, azithromycin

Renal Impairment

• Require dose adjustment: Aminoglycosides, vancomycin, fluoroquinolones, beta-lactams

Antibiotic Stewardship Principles

1. Obtain cultures before starting antibiotics when possible 1
2. Use the narrowest spectrum agent effective against the suspected pathogen 1
3. Reassess therapy at 48-72 hours based on clinical response and culture results 1
4. De-escalate to targeted therapy when possible 1
5. Use the shortest effective duration to minimize resistance development 1

Common Pitfalls to Avoid

1. Overuse of broad-spectrum antibiotics for uncomplicated infections
2. Inadequate dosing leading to treatment failure or resistance
3. Prolonged therapy beyond recommended duration
4. Failure to adjust therapy based on culture results
5. Inappropriate antibiotic selection for the suspected pathogen

Remember that local resistance patterns should guide empiric therapy choices, and treatment should be adjusted based on culture results whenever available.