Antibiotic selection
The initial drug of choice for treatment of mastitis is dicloxacillin sodium 500 mg every 6 hours for 7 to 10 days. If the patient has a mild allergy to penicillin, the appropriate alternative is cephalexin 500 mg every 8 hours for 7 to 10 days. If the patient’s allergy to penicillin is severe, 2 alternatives are possible. One is clindamycin 300 mg twice daily for 7 to 10 days; the other is trimethoprim-sulfamethoxazole double strength (800 mg/160 mg), twice daily for 7 to 10 days. The latter 2 drugs are also of great value if the patient fails to respond to initial therapy and/or infection with methicillin-resistant Staphylococcus aureus (MRSA) is suspected.2 I prefer the latter agent because it is less expensive than clindamycin and is less likely to cause antibiotic-induced diarrhea.
If hospitalization is required, the drug of choice is intravenous vancomycin. The appropriate dosage is 20 mg/kg every 8 to 12 hours (maximum single dose of 2 g).2
10. Syphilis
Syphilis is caused by the spirochete bacterium, Treponema pallidum. The diagnosis can be made by clinical examination if the characteristic findings listed in TABLE 2 are present.2,17 However, most patients in our practice will have latent syphilis, and the diagnosis must be established based on serologic screening.17
Antibiotic selection
In pregnancy, the treatment of choice for syphilis is penicillin (TABLE 3).2,10,17 Only penicillin has been proven effective in treating both maternal and fetal infection. If the patient has a history of allergy to penicillin, she should undergo skin testing to determine if she is truly allergic. If hypersensitivity is confirmed, the patient should be desensitized and then treated with the appropriate regimen outlined in TABLE 3. Of interest, within a short period of time after treatment, the patient’s sensitivity to penicillin will be reestablished, and she should not be treated again with penicillin unless she undergoes another desensitization process.2,17
11. Trichomoniasis
Trichomoniasis is caused by the flagellated protozoan, Trichomonas vaginalis. The condition is characterized by a distinct yellowish-green vaginal discharge. The vaginal pH is >4.5, and motile flagellated organisms are easily visualized on saline microscopy. The vaginal panel assay also is a valuable diagnostic test.3
Antibiotic selection
The drug of choice for trichomoniasis is oral metronidazole 500 mg twice daily for 7 days. The patient’s sexual partner(s) should be treated concurrently to prevent reinfection. Most treatment failures are due to poor compliance with therapy on the part of either the patient or her partner(s); true drug resistance is uncommon. When antibiotic resistance is strongly suspected, the patient may be treated with a single 2-g oral dose of tinidazole.2
12. Urinary tract infections
Urethritis
Acute urethritis usually is caused by C trachomatis or N gonorrhoeae. The treatment of infections with these 2 organisms is discussed above.
Asymptomatic bacteriuria and acute cystitis
Bladder infections are caused primarily by E coli, Klebsiella pneumoniae, and Proteus species. Gram-positive cocci such as enterococci, Staphylococcus saprophyticus, and GBS are less common pathogens.18
The key diagnostic criterion for asymptomatic bacteriuria is a colony count greater than 100,000 organisms/mL of a single uropathogen on a clean-catch midstream urine specimen.18
The usual clinical manifestations of acute cystitis include frequency, urgency, hesitancy, suprapubic discomfort, and a low-grade fever. The diagnosis is most effectively confirmed by obtaining urine by catheterization and demonstrating a positive nitrite and positive leukocyte esterase reaction on dipstick examination. The finding of a urine pH of 8 or greater usually indicates an infection caused by Proteus species. When urine is obtained by catheterization, the criterion for defining a positive culture is greater than 100 colonies/mL.18
Antibiotic selection. In the first trimester, the preferred agents for treatment of a lower urinary tract infection are oral amoxicillin (875 mg twice daily) or cephalexin (500 mg every 8 hours). For an initial infection, a 3-day course of therapy usually is adequate. For a recurrent infection, a 7- to 10-day course is indicated.
Beyond the first trimester, nitrofurantoin monohydrate macrocrystals (100 mg orally twice daily) or trimethoprim-sulfamethoxazole double strength (800 mg/160 mg twice daily) are the preferred agents. Unless no other oral drug is likely to be effective, these 2 drugs should be avoided in the first trimester. The former has been associated with eye, heart, and cleft defects. The latter has been associated with neural tube defects, cardiac anomalies, choanal atresia, and diaphragmatic hernia.18
Acute pyelonephritis
Acute infections of the kidney usually are caused by the aerobic gram-negative bacilli: E coli, K pneumoniae, and Proteus species. Enterococci, S saprophyticus, and GBS are less likely to cause upper tract infection as opposed to bladder infection.
The typical clinical manifestations of acute pyelonephritis include high fever and chills in association with flank pain and tenderness. The diagnosis is best confirmed by obtaining urine by catheterization and documenting the presence of a positive nitrite and leukocyte esterase reaction. Again, an elevated urine pH is indicative of an infection secondary to Proteus species. The criterion for defining a positive culture from catheterized urine is greater than 100 colonies/mL.2,18
Antibiotic selection. Patients in the first half of pregnancy who are hemodynamically stable and who show no signs of preterm labor may be treated with oral antibiotics as outpatients. The 2 drugs of choice are amoxicillin-clavulanate (875 mg twice daily for 7 to 10 days) or trimethoprim-sulfamethoxazole double strength (800 mg/160 mg twice daily for 7 to 10 days).
For unstable patients in the first half of pregnancy and for essentially all patients in the second half of pregnancy, parenteral treatment should be administered on an inpatient basis. My preference for treatment is ceftriaxone, 2 g intravenously every 24 hours. The drug provides excellent coverage against almost all the uropathogens. It has a convenient dosing schedule, and it usually is very well tolerated. Parenteral therapy should be continued until the patient has been afebrile and asymptomatic for 24 to 48 hours. At this point, the patient can be transitioned to one of the oral regimens listed above and managed as an outpatient. If the patient is allergic to β-lactam antibiotics, an excellent alternative is aztreonam, 2 g intravenously every 8 hours.2,18 ●