The purpose of this study is to investigate antibiotic treatment to target bacteria about the shoulder. This bacteria, Propionibacterium acnes, is detected in many revision shoulder surgeries and is thought to contribute to periprosthetic joint infections, pain, and failure of total shoulder arthroplasty as well as other shoulder surgeries. This study is investigating adding an FDA approved antibiotic that is commonly used for treatment of this bacteria and many common infections. The investigators will take intraoperative cultures to look for the presence or absence of specific bacteria. The investigators are conducting this trial to see if adding another antibiotic to specifically target this common bacteria found around the shoulder will be effective.

Patients undergoing total and reverse shoulder arthroplasty for primary glenohumeral arthritis will be invited to participate in this study if patients meet inclusion and exclusion criteria. Patients will be randomized to receive either standard perioperative antibiotics with cefazolin or to the treatment group to receive doxycycline in addition to cefazolin. Patients will then undergo routine surgical treatment. 3 cultures from the superficial tissue, dermis, and glenohumeral joint will be taken and cultured for 14 days to detect any bacterial growth.

Inclusion Criteria:

• Patients undergoing primary total shoulder arthroplasty at Rush University Medical Center

Exclusion Criteria:

• Patients with prior shoulder surgery of any kind
• Patients with a known infection or history of infection with clinical signs such as elevated erythrocyte sedimentation rate, C-reactive protein, positive culture aspiration
• Patients with a known allergy to doxycycline
• Patients with a known allergy to cefazolin or penicillin

Adverse events are recorded over the 1 year time period in which patients were recruited and participated in this study.