Medical Health Encyclopedia

Beta-Lactams

The beta-lactam antibiotics share common chemical features and include penicillins, cephalosporins, and some newer similar agents. Their primary actions to interfere with bacterial cell walls. Many have been important in the treatment of urinary tract infections.

Penicillins (Amoxicillin). Until recent years, the standard treatment for a UTI was 10 days of amoxicillin, a penicillin antibiotic, but it is now ineffective against E. coli bacteria in up to 25% of cases. A combination of amoxicillin-clavulanate (Augmentin) is sometimes given for drug-resistant infections. Amoxicillin or Augmentin may be useful for UTIs caused by gram-positive organisms, including Enterococcus species and S. saprophyticus.

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Cephalosporins. Antibiotics known as cephalosporins are also alternatives for infections that do not respond to standard treatments or for special populations. They are often classed in the following:

• First generation includes cephalexin (Keflex), cefadroxil (Duricef, Ultracef), and cephradine (Velosef).
• Second generation include cefaclor (Ceclor), cefuroxime (Ceftin), cefprozil (Cefzil), and loracarbef (Lorabid).
• Third generation include cefpodoxime (Vantin), cefdinir (Omnicef) cefditoren (Sprectracef), cefixime (Suprax), and ceftibuten (Cedex). Ceftriaxone (Rocephin) is an injected cephalosporin. These are effective against a wide range of gram-negative bacteria.

Other Beta-Lactam Agents. Other beta-lactam antibiotics have been developed. For example, pivmecillinam (a form of mecillinam), is commonly used in Europe for UTIs. It appears to be safe during pregnancy.

Trimethoprim-Sulfamethoxazole (TMP-SMX)

The current typical treatment is a three-day course of the combination drug trimethoprim-sulfamethoxazole, commonly called TMP-SMX (Bactrim, Cotrim, Septra). A one-day course is somewhat less effective but poses a lower risk for side effects. Longer courses (7 to 10 days) work no better than the three-day course and have a higher rate of side effects. TMP-SMX should not be used in patients whose infections occurred after dental work or in patients allergic to sulfa drugs. Allergic reactions can be very serious. Trimethoprim (Proloprim, Trimpex) is sometimes used alone in those allergic to sulfa drugs. TMP-SMX  can interfere with the effectiveness of oral contraceptives. High rates of bacterial resistance to TMP-SMX are being observed in parts of the US, such as the Southeast, Southwest, and southern California. Still, even when regional rates approach 30%, cure rates with TMP-SMX reach 80% to 85%.