In-out catheterization is ideal
I recommend that the urine sample be obtained by an in-out catheterization in symptomatic patients. This technique eliminates any concern about contamination of the specimen by vaginal organisms and provides a “pure” sample for culture. When urine is obtained by this method, the criterion for a positive culture result is greater than 100 colonies/mL.3 If the urine is obtained by the midstream clean-catch method, the cutoff for a positive culture remains greater than 100,000 colonies/mL.1,3
Unless the clinician is working in a low resource environment, the culture should always be obtained even though the patient will be empirically treated prior to the culture result being available. The culture can be helpful in guiding changes in antibiotic therapy if the initial response to treatment is poor.
In the first trimester, empiric treatment should be with amoxicillin or cephalexin. Beyond the first trimester, nitrofurantoin should be the drug of choice. This antibiotic is inexpensive and well-tolerated. It has limited effect on the bowel or vaginal flora and is unlikely to cause a secondary yeast infection or diarrhea. If a Proteus infection is suspected, however, trimethoprim-sulfamethoxazole double strength (800 mg/ 160 mg) should be used because this organism is not susceptible to nitrofurantoin. The duration of therapy should be a minimum of 3 days with the first infection and 7 to 10 days with recurrent infections.1,3,4
Acute pyelonephritis
Pyelonephritis may develop de novo or may result from inadequate treatment of lower urinary tract infection. The right kidney is affected in approximately 75% of cases because the right ureter is more subject to compression by the gravid uterus. The principal pathogen is E coli, although Klebsiella pneumoniae and Proteus species also are of importance. Other aerobic Gram-negative bacilli, such as Pseudomonas and Serratia species, are much less common unless the patient is immunosuppressed or has an indwelling catheter.1
The characteristic clinical manifestations of acute pyelonephritis are high fever (>39 °C), shaking chills, nausea and vomiting, and flank pain and tenderness. Increased frequency of urination and dysuria also may be present. In addition, pyelonephritis may be accompanied by preterm labor, sepsis, and acute respiratory distress syndrome (ARDS). The diagnosis is established by clinical findings, urinalysis, and urine culture. The urine specimen should be obtained by an in-out catheterization, analyzed initially by dipstick for nitrites and leukocyte esterase, and submitted for culture and sensitivity. Blood cultures should be obtained, and chest radiography should be performed if ARDS is suspected.
Empiric treatment should be started as soon as these initial diagnostic tests are completed. Many women in the first 20 weeks of pregnancy will not be seriously ill and may be treated as outpatients. I recommend an initial dose of intramuscular ceftriaxone 2 g followed by oral amoxicillin-clavulanate (875 mg twice daily) for a total of 10 days. If the patient is allergic to beta-lactam antibiotics, oral trimethoprim-sulfamethoxazole double strength (800 mg/160 mg) twice daily would be an excellent alternative.1,12
Treating seriously ill patients
Patients who are more seriously ill, particularly in the second half of pregnancy when preterm labor is more likely, should be hospitalized for supportive care (intravenous [IV] fluids, antipyretics, anti-emetics) and treatment with parenteral antibiotics.1,12 At our medical center, IV ceftriaxone (2 g every 24 hours), is the agent of choice. It has a convenient dosing schedule and covers almost all of the potential uropathogens. If an unusually drug-resistant organism is suspected, gentamicin or aztreonam can be combined with ceftriaxone to ensure complete coverage (see dosage recommendations below).
If the patient is allergic to beta-lactam antibiotics, alternative IV agents include:
- trimethoprim-sulfamethoxazole (8–10 mg/kg/d in 2 divided doses)
- gentamicin (5 mg/kg of ideal body weight every 24 hours)
- aztreonam (2 g every 8 hours)
Parenteral antibiotics should be administered until the patient has been afebrile and asymptomatic for 24 hours. At this point, oral antibiotics, based on sensitivity testing, can be started, and the patient can be discharged to complete a 10-day course of therapy.
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