Unasyn

SARASOTA, FLA. -- Newerantibiotics are not necessarily better than older ones for treating ob.gyn.-related infections, Dr. Patrick Duff said at a perinatal symposium sponsored by Symposia Medicus.

Dr. Duff, professor of ob.gyn. at the University of Florida in Gainesville, offered these suggestions on how and when to use some of the older antibiotics:

* Limited-Spectrum Penicillins. Penicillin and ampicillin are superb for covering group B streptococci and anaerobic streptococci, he said.

Ampicillin is "the drug of choice" for treating enterococcal urinary tract infection (UTI). However, don't rely on it as empiric therapy for just any UTI. The primary UTI pathogen is Escherichia coli, and the secondary pathogen is Klebsiella. Neither penicillin nor ampicillin provide adequate coverage of coliforms. In fact, up to 30% of E. coli strains and more than 50% of Klebsiella strains are resistant to ampicillin, Dr. Duff noted.

Penicillin does not cover enterococci; neither of the drugs cover Bacteroides or staphylococci well, so they're not an option for treating mastitis, he noted at the symposium, which was also sponsored by Sarasota Memorial Hospital.

* Extended-Spectrum Penicillins. All pelvic pathogens can be treated with extended-spectrum penicillins, including mezlocillin and piperacillin and combination agents such as ampicillin-sulbactam (Unasyn), piperacillin-tazobactam (Zosyn), and ticarcillin-clavulanic acid (Timentin).

These drugs are interchangeable and provide very good coverage against Bacteroides. Drug selection should be made on the basis of expense, said Dr. Duff, noting that the combination drugs usually cost less.

* Cephalosporins. Much of the confusion caused by the abundance of drugs in the cephalosporin category can be avoided by ranking them in terms of coverage spectrum rather than by generation.

The extended-spectrum cephalosporins--cefoxitin, cefotetan, cefotaxime, ceftizoxime, and cefepime--are the most applicable to ob.gyn. practice. They can be used as monotherapy to treat polymicrobial pelvic infections; they're therapeutically interchangeable; and they provide good coverage against most pelvic pathogens, with the exception of enterococci.

Selection should be based on cost; cefoxitin tends to be the most expensive and cefotetan the least expensive.

Limited-spectrum cephalosporins, including cefazolin and cephapirin, are "excellent" against anaerobic streptococci and group B streptococci, making them inexpensive options for treating mastitis.

Limited-spectrum cephalosporins provide coverage against E. coli, Klebsiella, and proteus strains comparable to penicillin. But they are not effective against enterococci, Bacteroides, or Prevotella.

Of all the intermediate-spectrum cephalosporins, ceftriaxone is unique because of its unparalleled effectiveness against Neisseria gonorrhoeae, he said.

In general, intermediate-spectrum cephalosporins, such as cefonicid and cefoperazone, are also good for group B streptococci, staphylococci, coliforms, and anaerobic streptococci. They don't provide coverage against enterococci, some coliforms, Bacteroides, or Prevotella.

* Carbapenems. Imipenem-cilastatin and meropenem provide the best activity of all antibiotics against a very broad range of pelvic pathogens, Dr. Duff said.

Yet these are not the best choices for most patients because there are far less expensive drugs available to treat the majority of infections encountered.

"I would save these for serious life-threatening infections, particularly in immune-compromised patients where you don't want to use combinations that include aminoglycosides," Dr. Duff said.

Metronidazole is preferred over clindamycin by some physicians because it has slightly better anaerobic coverage. However, it should be used with a limited-spectrum penicillin for gram-positive coverage and with an aminoglycoside for gram-negative coverage.

Clindamycin, used in combination with aminoglycosides gentamicin, is effective against staphylococci and group B streptococci.

* Aminoglycosides. The three available aminoglycosides--gentamicin, tobramycin, and amikacin--all provide superb coverage against aerobic gram-negative rods and staphylococci. Gentamicin comes in generic form and is the best buy, Dr. Duff said.

Amikacin, however, has slightly better coverage of aerobic gram-negative rods and would be a better choice for immune-compromised patients or in a setting in which drug-resistant organisms are prevalent.

Fluoroquinolones. "What you want to remember about [fluoroquinolones] is that they don't cover group B streptococci very well, they are very good against staphylococci and hemophilus influenza, and they are good for patients with community-acquired pneumonia who are allergic to penicillin," Dr. Duff said.

Fluoroquinolones are valuable in gynecology because of their coverage of gonorrhea and aerobic gram-negative rods. The newer ones--such as lomefloxacin, sparfloxacin, and trovafloxacin--are better against anaerobes than the older ones.

All are good for uncomplicated gonorrhea and for UTIs caused by resistant pathogens, though they should not be used as first-line agents because of their high cost. Trovafloxacin and ofloxacin are also effective in treating chlamydia.

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