Specific Antibiotics Used for Most UTIs
Beta-Lactams
The beta-lactam antibiotics share common chemical features and include penicillins, cephalosporins, and some newer similar drugs. 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.
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 as:
- 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 Drugs. 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 typical treatment is a 3-day course of the combination drug trimethoprim-sulfamethoxazole, commonly called TMP-SMX (Bactrim, Cotrim, Septra). A 1-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 3-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 exist in many parts of the U.S. Still, even when regional rates approach 30%, cure rates with TMP-SMX reach 80% to 85%.
Fluoroquinolones (Quinolones)
Fluoroquinolones (also simply called quinolones) are now becoming as widely used as TMP-SMX. These drugs interfere with the bacteria's genetic material so they cannot reproduce. They are the standard alternatives to TMP-SMX. Examples of quinolones include ofloxacin (Floxacin), ciprofloxacin (Cipro), norfloxacin (Noroxin), levofloxacin (Levaquin), gatifloxacin (Tequin), and sparfloxacin (Zagam). These antibiotics are effective against a wide range of organisms but are expensive and, in general, used in the following circumstances:
- In patients with complicated or catheter-induced UTIs
- In patients who do not respond or who are allergic to TMP-SMX
- In communities where there are high rates of bacteria resistant to TMP-SMX
- In elderly patients. A 2001 study of older women with UTIs (mean age 80), about half of whom were living in nursing homes, found that 96% responded to ciprofloxacin, compared with 87% to TMP-SMX.
Pregnant women should not take fluoroquinolone antibiotics. They also have more adverse effects in children than other antibiotics and should not be the first-line option in most situations.
Antibiotics Used Specifically for UTIs
Nitrofurantoin. Nitrofurantoin (Furadantin, Macrodantin) is a relatively inexpensive antibiotic that is used specifically for urinary tract infections. It is an effective alternative to TMP-SMX or a quinolone. Unlike many of the other drugs, however, it must be given 7 to 10 days, even in cases of simple cystitis. (Shorter course treatments are being investigated.) It is not useful for treating kidney infections. Nitrofurantoin frequently causes stomach upset and interacts with many drugs. Other chronic or serious medical conditions may also affect its use. It should not be used in pregnant women within 1 to 2 weeks of delivery, in nursing mothers, or in those with kidney disease.
Fosfomycin. The antibiotic fosfomycin (Monurol), which comes in an orange-flavored, soluble powder, is proving to be another good alternative. It can be an effective 1-dose treatment for many women, including those who are pregnant. To date, bacterial resistance rates to this antibiotic are very low.
Tetracyclines
Tetracyclines inhibit bacterial growth. They include doxycycline, tetracycline, and minocycline. Long-term treatment with tetracycline or doxycycline may be used for infections that are caused by Mycoplasma or Chlamydia. Tetracyclines have unique side effects among antibiotics, including skin reactions to sunlight, possible burning in the throat, and tooth discoloration.
Aminoglycosides
Aminoglycosides (gentamicin, kanamycin, tobramycin, amikacin) are given by injection for very serious bacterial infections. They can be given only in combination with other antibiotics. Gentamicin is the most commonly used aminoglycoside for serious UTIs. They can have very serious side effects, including damage to hearing, sense of balance, and kidneys.
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