Antipseudomonal Penicillins

Agents: piperacillin, mezlocillin, carbenicillin,  ticarcillin

None of the penicillins we have discussed thus far offer appreciable activity against  Pseudomonas aeruginosa, a common nosocomial pathogen that is often resistant to multiple antibiotics. Enter the antipseudomonal penicillins. These agents are active against  Pseudomonas aeruginosa and other more drug-resistant GNRs. However, they are just  as susceptible to beta-lactamases as penicillin andampicillin, so they are not antistaphylococcal. Also,  strains of GNRs that produce beta-lactamases are resistant to them. They do have activity against streptococci and enterococci.

Spectrum

Good: Pseudomonas aeruginosa, streptococci, enterococci

Moderate: enteric GNRs, Haemophilus

Poor : staphylococci, anaerobes

Adverse Effects

Similar to those of other beta-lactams.

Important Facts

• These drugs retain the Gram-positive activity of penicillin and are active against many streptococci and enterococci.

• Antipseudomonal penicillins can be used by themselves or, more commonly, in combination with a beta-lactamase inhibitor.

• Piperacillin is the most frequently prescribed of these agents. It has stronger antipseudomonal activity than ticarcillin. Carbenicillin may be administered orally, but it does not achieveuseful concentrations for the treatment of anything except UTIs. Mezlocillin is not commonly used.

What They’re Good For

Infections caused by susceptible  Pseudomonas or other GNRs. If a Gram-positive organism is susceptible to an antipseudomonal penicillin, it will be susceptible to at least one narrower-spectrum penicillin as well, and the narrower-spectrum drug should generally be used.

Don’t Forget!

These drugs are useful step-down agents in the treatment of infections caused by  Pseudomonas aeruginosa. However, they are not good empiric therapeutic choices, because other GNRs that cause nosocomial infections may be resistant to them (such as E. coli). Start with a beta-lactamase-resistant agent, then change your therapy to an antipseudomonal penicillin if susceptibilities allow.

References

Gallagher ,J.C. and MacDougall ,c. (2012). Antibiotics Simplified. Second Edition. Jones & Bartlett Learning, LLC.