Sexually transmitted infections (STIs) have steadily increased over the last decade and continue to pose a serious risk to public health. Chlamydia trachomatis is the most frequently reported bacterial STI in the US with over 2.4 million cases reported in 2020 and nearly $700 million in direct medical costs [1]. Although curable with adequate treatment, chlamydial infections most commonly present as asymptomatic and can lead to serious complications such as pelvic inflammatory disease (PID), ectopic pregnancies, or infertility if left untreated. Therefore, both annual screening and prompt management are recommended to prevent complications and transmission to sexual partners.

Due to the frequency of co-infection with Neisseria gonorrhea, combination antibiotic therapy has been recommended by the Center for Disease Control (CDC) since 1985 if the other infection has not been excluded [2]. The 2010 and 2015 CDC STI treatment guidelines recommended single doses of ceftriaxone 250 mg intramuscular (IM) injection and azithromycin 1 g by mouth for possible coinfection of chlamydia and gonorrhea [11,12]. This was the common practice for STI management until the recommendation was updated in the 2021 CDC STI treatment guidelines. Based on the latest evidence, the current recommendation is a single dose of ceftriaxone 500 mg IM injection for gonorrhea and oral doxycycline for 7 days for concerns of coinfection with chlamydia [10,13].

Original meta-analysis data from 2004 compiled 12 different clinical trials and showed similar cure rates and equal efficacy when comparing azithromycin and doxycycline for genital chlamydia infections [6]. With increasing antimicrobial resistance and more sensitive nucleic acid amplification tests, a repeat meta-analysis was performed in 2014 and demonstrated a small increased efficacy in doxycycline over azithromycin [5]. Since then, more clinical data has evolved favoring doxycycline due to lower treatment failure rates and increased efficacy in rectal chlamydia infections. Two randomized controlled trials published in 2021 evaluated the microbiologic cure rate of rectal chlamydia infections at 4 weeks in men who have sex with men (MSM). These studies demonstrated a difference in cure rate of over 20% in favor of doxycycline, which further strengthens the CDC's guideline recommendation [3,7]. An increase in cure rates was also demonstrated in women with concurrent vaginal and rectal chlamydial infections in the FemCure and CHLAZIDOXY studies [4,9]. There is also a proposed benefit of increased efficacy for doxycycline in treating pharyngeal chlamydia, but evidence to support this claim is limited to an observational study [8]. Overall, the evidence supporting the guideline change to doxycycline first line for chlamydial infections is robust, but there are still drawbacks to this regimen that must be considered.

There is a significant public health concern regarding patient nonadherence to the 7-day course of doxycycline when compared to the previous one-time dose azithromycin administered within the ED. Nonadherence creates an increased risk of disease transmission, as well as serious reproductive health problems in the long-term. The infection is ultimately only treated if the doxycycline prescription is filled, picked up from the pharmacy, and taken as directed. There was an observational study published in 1998 that showed a 24% doxycycline noncompliance rate using Medication Event Monitoring System (MEMS) technology at two STI clinics in the US [16]. Similarly, a 1999 study using the same technology compared MEMS compliance data to self-reported doxycycline compliance for STIs. They reported that 90% of patients reported taking their doxycycline as directed, but only 16% achieved complete compliance according to the MEMS data [17]. Lastly, there was a retrospective cohort study performed in pediatrics that assessed prescription filling of STI-related antimicrobial treatment. Their results indicated that only 57.7% of prescriptions were filled at outpatient pharmacies [18]. Since the 2021 guideline update, there are no recent studies predominantly assessing the adherence of patients to the recommended 7-day course of doxycycline for chlamydial infections. Therefore, the objective of this study was to evaluate patient's adherence to doxycycline for Chlamydia trachomatis infections after discharge from the ED.