This patient has clinical evidence of pelvic inflammatory disease (PID) and should be treated with cefoxitin plus doxycycline. Although the ultrasonographic findings excluded a tubo-ovarian abscess, nausea and vomiting and inability to tolerate an oral treatment regimen are indications for hospital admission and initial parenteral therapy. PID occurs primarily in sexually active women, with Chlamydia trachomatis and Neisseria gonorrhoeae implicated in approximately two thirds of patients. However, PID is considered a polymicrobial infection that may also involve vaginal organisms, including anaerobes, enteric gram-negative rods, and streptococci. Additionally, organisms associated with bacterial vaginosis, such as Gardnerella vaginalis, may play a role. Therefore, antibiotic therapy with coverage directed to C. trachomatis and N. gonorrhoeae is essential, with broader-spectrum coverage to treat other potentially causative organisms. The antibiotic regimen of choice for patients who are hospitalized with PID is cefoxitin or cefotetan (second-generation cephalosporins) plus intravenous doxycycline.

Ceftriaxone plus azithromycin can be used in single-dose regimens for uncomplicated cervicitis, but this regimen is not recommended for treatment of PID. Ceftriaxone as a single-dose intramuscular injection plus a 14-day course of oral doxycycline (with or without metronidazole) can be used to treat PID in patients who do not have an indication for hospitalization. In this patient, symptoms of nausea and vomiting raise concern for the ability to tolerate oral therapy and are an indication for hospitalization. Ciprofloxacin is no longer recommended for an infection requiring coverage for N. gonorrhoeae because fluoroquinolone resistance is common with this organism.

Piperacillin-tazobactam does not provide coverage for C. trachomatis and would not be appropriate monotherapy in this patient. Additionally, although PID is considered a polymicrobial infection, and piperacillin-tazobactam would provide coverage for Enterobacteriaceae and anaerobes, it is also an antipseudomonal agent and is unnecessarily broad spectrum for this patient.