For more than 130 years, appendectomy (surgery to remove the appendix) has been the standard treatment for appendicitis. But recent European studies have challenged the belief that surgery is the best option by showing that antibiotics alone can work to treat this common condition.

Results from six randomized clinical trials involving over 1,700 patients have shown that antibiotics can treat appendicitis safely and successfully without surgery. These results are starting to change the way European surgeons treat appendicitis, but surgeons in the United States have pointed to problems with these studies and are reluctant to change their practice until a large-scale trial is conducted. As of 2015, nearly all patients with appendicitis in the United States (approximately 97.5 percent) were treated with surgery.

Given the studies done in Europe, surgeons and patients in the United States are starting to ask, “Is it time to change our approach to treating appendicitis from offering appendectomy first to offering antibiotics first?” CERTAIN developed the Comparing Outcomes of Drugs & Appendectomy (CODA) study to answer this important question.

Our Study

CODA is a large-scale, randomized trial comparing appendectomy to antibiotics first for the treatment of uncomplicated appendicitis. It focuses on both clinical outcomes—broadly agreed, measurable changes in health or quality of life—as well as the patient-reported outcomes (PROs) that matter most to patients.

Study participants may have surgery or they may take antibiotics. Most patients will have their treatment decided randomly, with an equal chance of getting either treatment. The study will also include patients who do not want their treatment decided randomly. No matter which treatment a patient gets, doctors and nurses will help control their pain and treat their appendicitis.

Results of this study will help patients better understand the difference between surgery and antibiotics. It will also tell us if certain patients would benefit more from one treatment than the other and help nearly 300,000 Americans each year make an important healthcare decision.

Past studies have not evaluated whether or not the benefits of possibly avoiding surgery outweighed the risks and anxiety patients may feel about future episodes of appendicitis. No studies to date have compared the impact of these two appendicitis treatments on the overall patient experience or included PROs in addition to clinical outcomes. In short, the studies to date have not asked “Is antibiotics first as good a treatment for me as appendectomy?” and that is what the CODA trial aims to address.

Coordinating Institution

The University of Washington’s Surgical Outcomes Research Center (SORCE) in Seattle, Wash., is leading the Clinical and Stakeholder Coordinating Center. The UW Center for Biomedical Statistics is serving as the Data Coordinating Center.

Investigators at SORCE are coordinating the study at the University of Washington Medical Center (UWMC) and other clinical sites in Washington state. Investigators at Olive View-UCLA Medical Center in Sylmar, Calif., are coordinating the study there and at other clinical sites in California.


The CODA study is funded by a grant from the Patient Centered Outcomes Research Institute (PCORI).

Learn about the study team.

Learn about the study sites.