Neither Ampicillin Nor Ceftazidime Provide Adequate Coverage for Bullous Impetigo
Neither ampicillin nor ceftazidime should be used to treat bullous impetigo, as both agents lack reliable activity against Staphylococcus aureus, which is the exclusive causative pathogen of this condition. 1, 2
Why These Agents Are Inappropriate
Ampicillin's Critical Gap in Coverage
- Ampicillin is completely ineffective against penicillinase-producing staphylococci, which constitute the vast majority of S. aureus isolates causing impetigo 3
- The FDA label explicitly states that ampicillin "is inactivated by penicillinase and therefore is ineffective against penicillinase-producing organisms including certain strains of staphylococci" 3
- Bullous impetigo is caused exclusively by toxin-producing S. aureus, making ampicillin an inappropriate choice 1, 2
Ceftazidime's Spectrum Mismatch
- Ceftazidime is a third-generation cephalosporin designed primarily for gram-negative coverage, particularly Pseudomonas aeruginosa, and has poor activity against gram-positive organisms like S. aureus 4
- While the FDA label lists S. aureus in its spectrum, ceftazidime was explicitly excluded from WHO guidelines for skin infections because it is "suitable for targeted treatment but not empiric treatment" of staphylococcal infections 5
- The drug's design prioritizes gram-negative pathogens over the gram-positive cocci that cause impetigo 4
Recommended First-Line Alternatives
For Presumed Methicillin-Susceptible S. aureus (MSSA)
- Cephalexin 25-50 mg/kg/day divided into 4 doses for 7 days is the first-line oral antibiotic recommended by the American Academy of Pediatrics and IDSA 5, 1
- Dicloxacillin at the same dosing is an equally effective alternative 5, 1
- Both agents are penicillinase-stable and provide reliable anti-staphylococcal coverage 6
When MRSA is Suspected or Confirmed
- Clindamycin 20-30 mg/kg/day divided into 3 doses for 7 days provides excellent coverage 5, 1
- Sulfamethoxazole-trimethoprim (SMX-TMP) 8-12 mg/kg/day divided into 2 doses for 7 days is another effective option 5, 1
- Doxycycline 2-4 mg/kg/day divided into 2 doses for 7 days can be used in children over 8 years old 5, 1
Critical Clinical Considerations
Pathogen-Specific Treatment
- Bullous impetigo is caused exclusively by S. aureus, unlike non-bullous impetigo which may involve Streptococcus pyogenes 1, 2
- Studies demonstrate that S. aureus is isolated in 100% of bullous impetigo cases and in 62-81% of all impetigo cases overall 7, 6
- This makes anti-staphylococcal coverage absolutely essential 2, 7
Common Pitfall to Avoid
- Do not use penicillin V or ampicillin for impetigo treatment, as clinical trials show treatment failure rates of 24% with penicillin V compared to 0-4% with appropriate anti-staphylococcal agents 6
- The historical use of penicillin for impetigo is outdated and no longer appropriate given current pathogen profiles 8, 6