Aminopenicillins: Ampicillin and Amoxicillin

Aminopenicillins

• Ampicillin (IV) and Amoxicillin (PO) are aminopenicillins that cover some Gram positives (Streptococcus, Enterococcus, Listeria) but not MSSA.
• They have limited Gram negative coverage, with notable holes in Klebsiella, Moraxella, and SPICE A organisms.
• Aminopenicillins are used to treat upper respiratory infections, sinusitis, otitis media, cellulitis, Listeria infections, UTIs, and early Lyme disease.
• Amoxicillin is the best-absorbed beta lactam (75-90% bioavailability) and is used to treat Enterococcal infections if susceptible (E. faecalis generally susceptible, E. faecium usually not).
• Aminopenicillins can be used with aminoglycosides for synergy in Enterococcal endocarditis.

Anti-Staphylococcal Penicillins

• Methicillin / Nafcillin / Oxacillin (IV) and Dicloxacillin (PO) are anti-Staphylococcal penicillins that cover MSSA and Streptococcus.
• They are used to treat MSSA infections (unless PCN sensitive, which is rare), cellulitis, osteomyelitis, endocarditis, and bacteremia from MSSA.
• They do not cover MRSA and Coag negative Staph is usually resistant (>80%).
• Dicloxacillin is a reasonable oral choice for non-severe cellulitis; for serious MSSA infections, the entire course of therapy must be given intravenously.
• Nafcillin tends to be better tolerated than Oxacillin (less hepatitis and rash).

Anti-pseudomonal PCNs

• Piperacillin and Ticarcillin are anti-pseudomonal PCNs that are usually combined with beta lactamase inhibitors, which confers broader activity.
• The beta-lactamase component does not add activity against Pseudomonas, so if Pseudomonas is sensitive, Piperacillin alone could be used.

This quiz covers the properties and uses of aminopenicillins, including their spectrum, indications, and limitations. It also discusses their strengths and weaknesses in treating various infections.