CASSETTE - clindamycin adjunctive therapy for severe Staphylococcus aureus treatment evaluation: study protocol for a randomised controlled trial

Background: Exotoxins are an important virulence factors in Staphylococcus aureus. Clindamycin, a protein synthesis inhibitor antibiotic, is thought to limit exotoxin production and improve outcomes in severe S. aureus infections. However, randomised prospective data to support this is lacking. Methods: An open label, multicenter, randomised controlled trial (RCT) will compare outcome differences in severe S. aureus infection between a standard treatment (flucloxacillin/cefazolin in methicillin-susceptible S. aureus; and vancomycin/daptomycin in methicillin-resistance S. aureus) and a standard treatment plus an additional clindamycin given for 7 days. We will include a minimum of 60 participants (both adult and children) in the pilot study. Participants will be enrolled within 72 hours of an index culture. Severe infections will include septic shock, necrotising pneumonia, or multifocal and non-contiguous skin and soft tissue/osteoarticular infections. Immunosuppressed, moribund, current severe diarrhea or C. difficile infection, pregnant, and those with anaphylaxis to beta-lactams or lincosamides will be excluded. Primary outcomes measure is number of days alive and free (1 or none) of SIRS (Systemic Inflammatory Response Syndrome) within the first 14 days post randomization. Secondary outcomes measure will include all-cause mortality at 14, 42 and 90 days, time to resolution of SIRS, proportion with microbiological treatment failure, and rate of change of C-reactive protein over time. Impacts of inducible clindamycin resistance, strains types, methicillin-susceptibility, and presence of various exotoxins will also be analysed. Discussion: This study will assess the effect of adjunctive clindamycin on patient-centered outcomes in severe, toxin mediated S. aureus infections. The Pilot study will provide feasibility for a much larger RCT. Trial Registration: Australian New Zealand Clinical Trials Registry: ACTRN12617001416381p. Registered 06 October 2017 Keywords: Staphylococcus aureus, exotoxins, prospective studies, clindamycin, leukocidins