5. Chorioamnionitis
Chorioamnionitis is a polymicrobial infection caused by anaerobes, aerobic gram-negative bacilli (predominantly Escherichia coli), and aerobic gram-positive cocci (primarily group B streptococci [GBS]). The diagnosis usually is made based on clinical examination: maternal fever, maternal and fetal tachycardia, and no other localizing sign of infection. The diagnosis can be confirmed by obtaining a sample of amniotic fluid via amniocentesis or via aspiration through the intrauterine pressure catheter and demonstrating a positive Gram stain, low glucose concentration (<20 mg/dL), positive nitrites, positive leukocyte esterase, and ultimately, a positive bacteriologic culture.2
Antibiotic selection
The initial treatment of chorioamnionitis specifically targets the 2 major organisms that cause neonatal pneumonia, meningitis, and sepsis: GBS and E coli. For many years, the drugs of choice have been intravenous ampicillin (2 g every 6 hours) plus intravenous gentamicin (5 mg/kg of IBW every 24 hours). Gentamicin also can be administered intravenously at a dose of 1.5 mg/kg every 8 hours. I prefer the once-daily dosing for 3 reasons:
- Gentamicin works by a concentration-dependent mechanism; the higher the initial serum concentration, the better the killing effect.
- Once-daily dosing preserves long periods with low trough levels, an effect that minimizes ototoxicity and nephrotoxicity.
- Once-daily dosing is more convenient.
In a patient who has a contraindication to use of an aminoglycoside, aztreonam (2 g intravenously every 8 hours) may be combined with ampicillin.2
If the patient delivers vaginally, 1 dose of each drug should be administered postpartum, and then the antibiotics should be discontinued. If the patient delivers by cesarean, a single dose of a medication with strong anaerobic coverage should be administered immediately after the infant’s umbilical cord is clamped. Options include clindamycin (900 mg intravenously) or metronidazole (500 mg intravenously).11
There are 2 key exceptions to the single postpartum dose rule, however. If the patient is obese (body mass index [BMI] >30 kg/m2) or if the membranes have been ruptured for more than 24 hours, antibiotics should be continued until she has been afebrile and asymptomatic for 24 hours.12
Two single agents are excellent alternatives to the combination ampicillin-gentamicin regimen. One is ampicillin-sulbactam, 3 g intravenously every 6 hours. The other is piperacillin-tazobactam, 3.375 g intravenously every 6 hours. These extended-spectrum penicillins provide exceptionally good coverage against the major pathogens that cause chorioamnionitis. Although more expensive than the combination regimen, they avoid the potential ototoxicity and nephrotoxicity associated with gentamicin.2
6. Endometritis
Puerperal endometritis is significantly more common after CD than after vaginal delivery. The infection is polymicrobial, and the principal pathogens are anaerobic gram-positive cocci, anaerobic gram-negative bacilli, aerobic gram-negative bacilli, and aerobic gram-positive cocci. The diagnosis usually is made almost exclusively based on clinical findings: fever within 24 to 36 hours of delivery, tachycardia, mild tachypnea, and lower abdominal/pelvic pain and tenderness in the absence of any other localizing sign of infection.13
Antibiotic selection
Effective treatment of endometritis requires administration of antibiotics that provide coverage against the broad range of pelvic pathogens. For many years, the gold standard of treatment has been the combination regimens of clindamycin plus gentamicin or metronidazole plus ampicillin plus gentamicin. These drugs are available in generic form and are relatively inexpensive. However, several broad-spectrum single agents are now available for treatment of endometritis. Although they are moderately more expensive than the generic combination regimens, they usually are very well tolerated, and they avoid the potential nephrotoxicity and ototoxicity associated with gentamicin. TABLE 1 summarizes the dosing regimens of these various agents and their potential weaknesses in coverage.2,13
7. Gonorrhea
Gonorrhea is caused by the gram-negative diplococcus, Neisseria gonorrhoeae. The organism has a propensity to infect columnar epithelium and uroepithelium, and, typically, it causes a localized infection of the urethra, endocervix, and rectum. The organism also can cause an oropharyngeal infection, a disseminated infection (most commonly manifested by dermatitis and arthritis), and perihepatitis.
The diagnosis is best confirmed by a NAAT that can simultaneously test for gonorrhea and chlamydia in urine or in secretions obtained from the urethra, endocervix, and rectum.2,10
Antibiotic selection
The drugs of choice for treating uncomplicated gonococcal infection in pregnancy are a single dose of ceftriaxone 500 mg intramuscularly, or cefixime 800 mg orally. If the patient is allergic to β-lactam antibiotics, the recommended treatment is gentamicin 240 mg intramuscularly in a single dose, combined with azithromycin 2,000 mg orally.14
8. Group B streptococci prophylaxis
The first-line agents for GBS prophylaxis are penicillin and ampicillin. Resistance of GBS to either of these antibiotics is extremely rare. The appropriate penicillin dose is 3 million U intravenously every 4 hours; the intravenous dose of ampicillin is 2 g initially, then 1 g every 4 hours. I prefer penicillin for prophylaxis because it has a narrower spectrum of activity and is less likely to cause antibiotic-associated diarrhea. The antibiotic should be continued until delivery of the neonate.2,15,16
If the patient has a mild allergy to penicillin, the drug of choice is cefazolin 2 g intravenously initially, then 1 g every 8 hours. If the patient’s allergy to β-lactam antibiotics is severe, the alternative agents are vancomycin (20 mg/kg intravenously every 8 hours infused over 1–2 hours; maximum single dose of 2 g) and clindamycin (900 mg intravenously every 8 hours). The latter drug should be used only if sensitivity testing has confirmed that the GBS strain is sensitive to clindamycin. Resistance to clindamycin usually ranges from 10% to 15%.2,15,16
9. Puerperal mastitis
The principal microorganisms that cause puerperal mastitis are the aerobic streptococci and staphylococci that form part of the normal skin flora. The diagnosis usually is made based on the characteristic clinical findings: erythema, tenderness, and warmth in an area of the breast accompanied by a purulent nipple discharge and fever and chills. The vast majority of cases can be treated with oral antibiotics on an outpatient basis. The key indications for hospitalization are severe illness, particularly in an immunocompromised patient, and suspicion of a breast abscess.2
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