Ampicillin and Cloxacillin are both antibiotics from the penicillin group, but they’re used for slightly different purposes.

Key differences

1. Spectrum of activity

• Ampicillin: Broad-spectrum
  Works against many Gram-positive and some Gram-negative bacteria (e.g., E. coli, H. influenzae, Salmonella).
• Cloxacillin: Narrow-spectrum
  Mainly effective against Gram-positive bacteria, especially penicillinase-producing Staphylococcus (Staph aureus).

2. Resistance to penicillinase

• Ampicillin: ❌ Not resistant
  Can be destroyed by bacterial enzymes (beta-lactamases).
• Cloxacillin: ✅ Resistant
  Designed to resist penicillinase, making it useful for resistant staph infections.