Infectious Disease Consult

Commonly used antibiotics in ObGyn practice

OBG Manag. 2022 May;34(5):29, 36-40 | doi: 10.12788/obgm.0191

References

Duff P. Maternal and perinatal infection in pregnancy: bacterial. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe’s Obstetrics: Normal and Problem Pregnancies, 8th ed. Elsevier; 2020: chapter 58.
Duff P. Antibiotic selection in obstetrics: making cost-effective choices. Clin Obstet Gynecol. 2002;45:59-72.
Wagenlehner FME, Cloutier DJ, Komirenko AS, et al; EPIC Study Group. Once-daily plazomicin for complicated urinary tract infections. N Engl J Med. 2019;380:729-740.
Leffler DA, Lamont JT. Clostridium difficile infection. N Engl J Med. 2015;372:1539-1548.
Duff P. Prevention of infection after cesarean delivery. Clin Obstet Gynecol. 2019;62:758-770.
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St Cyr S, Barbee L, Workowski KA, et al. Update to CDC’s treatment guidelines for gonococcal infection, 2020. MMWR Morbid Mortal Wkly Rep. 2020;69:1911-1916.
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Workowski KA, Bolan GA. Sexually transmitted disease treatment guidelines, 2015. MMWR Morbid Mortal Wkly Rep. 2015;64(RR3):1-137.
Duff P. UTIs in pregnancy: managing urethritis, asymptomatic bacteriuria, cystitis, and pyelonephritis. OBG Manag. 2022;34(1):42-46.
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Extended-spectrum penicillins

Three interesting combination extended-spectrum penicillins are used widely in our specialty. They are ampicillin/sulbactam, amoxicillin/clavulanate, and piperacillin/tazobactam. Ampicillin/sulbactam may be administered intramuscularly and intravenously. Piperacillin/tazobactam is administered intravenously; amoxicillin/clavulanate is administered orally.

Clavulanate, sulbactam, and tazobactam are β-lactamase inhibitors. When added to the parent antibiotic (amoxicillin, ampicillin, and piperacillin, respectively), they significantly enhance the parent drug’s spectrum of activity. These agents interfere with bacterial cell wall synthesis. They provide excellent coverage of aerobic gram-positive cocci, including enterococci; anaerobic gram-positive cocci; anaerobic gram-negative bacilli; and aerobic gram-negative bacilli. Their principal adverse effects include allergic reactions and antibiotic-associated diarrhea. They are moderately expensive.

The principal application of ampicillin/sulbactam and piperacillin/tazobactam in our specialty is as single agents for treatment of puerperal endometritis, postoperative pelvic cellulitis, and pyelonephritis. The usual role for amoxicillin/clavulanate is for oral treatment of complicated UTIs, including pyelonephritis in early pregnancy, and for outpatient therapy of mild to moderately severe endometritis following delivery or pregnancy termination.

Macrolides, monobactams, and additional antibiotics

Azithromycin

Azithromycin is a macrolide antibiotic that is in the same class as erythromycin and clindamycin. In our specialty, it has largely replaced erythromycin because of its more convenient dosage schedule and its better tolerability. It inhibits bacterial protein synthesis, and it is available in both an oral and intravenous formulation.

Azithromycin has an excellent spectrum of activity against the 3 major microorganisms that cause otitis media, sinusitis, and bronchitis: Streptococcus pneumoniae, H influenzae, and M catarrhalis. It also provides excellent coverage of Chlamydia trachomatis, Mycoplasma pneumoniae, and genital mycoplasmas; in high doses it provides modest coverage against gonorrhea.⁸ Unlike erythromycin, it has minimal GI toxicity and is usually very well tolerated by most patients. One unusual, but very important, adverse effect of the drug is prolongation of the Q-T interval.⁹

Azithromycin is now available in generic form and is relatively inexpensive. As a single agent, its principal applications in our specialty are for treatment of respiratory tract infections such as otitis media, sinusitis, and acute bronchitis and for treatment of chlamydia urethritis and endocervicitis.^8,10 In combination with ampicillin, azithromycin is used as prophylaxis in patients with preterm premature rupture of membranes (PPROM), and, in combination with cefazolin, it is used for prophylaxis in patients undergoing cesarean delivery.^1,2,5

Aztreonam

Aztreonam is a monobactam antibiotic. Like the cephalosporins and penicillins, aztreonam inhibits bacterial cell wall synthesis. It may be administered intramuscularly and intravenously, and its principal spectrum of activity is against aerobic gram-negative bacilli, which is similar to the aminoglycosides’ spectrum.

Aztreonam’s most likely adverse effects include phlebitis at the injection site, allergy, GI upset, and diarrhea. The drug is moderately expensive. In our specialty, aztreonam could be used as a single agent, in lieu of an aminoglycoside, for treatment of pyelonephritis caused by an unusually resistant organism. It also could be used in combination with clindamycin or metronidazole plus ampicillin for treatment of polymicrobial infections, such as chorioamnionitis, puerperal endometritis, and pelvic cellulitis.^1,2

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