Medical Letter consultants last reviewed the antimicrobial agents for treatment of bacterial infections in 1996. Because new drugs have emerged and new information about older agents is now available, recommendations are discussed again.

Pneumonia. In some areas of the United States, more than 30 percent of isolates of S. pneumoniae, the most common cause of community-acquired pneumonia, are relatively or highly resistant to penicillin and sometimes to cephalosporins. Haemophilus influenzae, Klebsiella pneumoniae, legionellae and tuberculosis infection should be considered in the differential diagnosis. In hospitalized patients, cefotaxime, ceftriaxone or high doses of penicillin administered intravenously are reasonable first choices.

Vancomycin may be required for highly resistant strains. In ambulatory patients, an oral macrolide (erythromycin, azithromycin or clarithromycin), doxycycline or a fluoroquinolone such as levofloxacin is recommended. Hospital-acquired bacterial pneumonia, often caused by gram-negative bacilli such as Klebsiella, should be initially treated with a third-generation cephalosporin, cefepime, ticarcillin/clavulanic acid or imipenem—with or without an aminoglycoside. In the intensive care unit, where Pseudomonas aeruginosa is common, imipenem or meropenem plus an aminoglycoside would be a good first choice of therapy.

Meningitis. The organisms most commonly responsible for bacterial meningitis are Streptococcus pneumoniae and Neisseria meningitidis. In adults and children older than two months, cefotaxime or ceftriaxone is recommended, plus vancomycin (with or without rifampin) to cover resistant pneumococci. Vancomycin and rifampin are stopped if the organism is found to be susceptible to cephalosporins. In patients who are allergic to penicillin, vancomycin (with or without rifampin) can be used for treatment of resistant pneumococci. In children, administration of dexamethasone before or at the same time as the first dose of antibiotics to decrease the incidence of hearing loss and neurologic complications remains a matter of controversy. However, it is recommended if the meningitis is due to H. influenzae. Because of the high incidence of group B streptococci in newborns, ampicillin plus cefotaxime, with or without gentamicin, is usually recommended.

Sepsis Syndrome. The third- or fourth-generation cephalosporins can be used to treat sepsis caused by many strains of gram-negative bacilli. The initial treatment should include either a third- or fourth-generation cephalosporin, ticarcillin/clavulanic acid, piperacillin/tazobactam, imipenem or meropenem—each with an aminoglycoside. If methicillin-resistant staphylococci are suspected, vancomycin is often recommended. If anaerobes are suspected in intra-abdominal or pelvic infections, treatment with ticarcillin-clavulanic acid, ampicillin-sulbactam, or cefoxitin or cefotetan, each with or without an aminoglycoside, is recommended.

Urinary Tract Infection. Uncomplicated urinary tract infections can be effectively treated with oral trimethoprim-sulfamethoxazole or fluoroquinolone. A three-day course is usually sufficient. For repeated infections, a fluoroquinolone, oral amoxicillin-clavulanic acid or an oral third-generation cephalosporin can be effective. Hospitalized patients may need an aminoglycoside in addition to the standard regimens.

editor's note: Medical Letter has produced a comprehensive guide to the antibacterial agents used to treat common infections. A list of trade names is included. For each of the infecting organisms, the drug of choice and alternatives are recommended. A cost analysis is also presented. It is a handy reference for any clinician.—b.a.