Fig. 1

Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) flow chart. Magnetic resonance imaging (MRI). (1) Baseline MRI according to the study protocol can be a maximum of 4 weeks old when treatment starts. A follow-up MRI is taken between 12 and 13 months after treatment start (i.e., 12 to 14 months after baseline MRI); (2) For safety: haematological parameters (leucocytes, thrombocytes, eosinophils, haemoglobin (Hb) and hematocrit (Ht)) and measures of kidney (creatinine) and liver function (ASAT/ALAT), every month or more frequently if clinically indicated. For scientific purposes: glucose, white cell counts and C-reactive protein (CRP) for further safety monitoring and evaluation of inflammatory mechanisms and genetics/epigenetics; (3) Blood pressure, pulse, auscultation of heart and lungs (safety); (4) Age, gender, Body Mass Index (BMI), ethnicity, marital status, educational level, work status, physical work load, leisure time activity, smoking habits, subjective health complaints, emotional distress, fear-avoidance beliefs, low back pain (LBP) history/duration (including previous treatment, e.g., surgery for disc herniation, physiotherapy, chiropractic), expectations about treatment effect, pain drawing; (5) Pain provocation tests (springing test, active flexion/extension of the lumbar spine) and neurological tests (muscle strength, toe-heel walking, sensibility, reflexes, straight-leg raising, i.e., Lasegue test/reverse Lasegue test); (6) Roland Morris Disability Questionnaire, also collected 6 and 9 months after start of treatment; (7) Pain monitoring (LBP intensity) weekly during treatment period, and at 6 and 9 months after start of treatment; (8) Oswestry Disability Index, leg pain, hours with low back pain during the last 4 weeks, symptom-specific well-being, health-related quality of life, sick leave, short tau inversion recovery (STIR) signal of Modic changes; (9) Patient’s satisfaction with treatment (5-point Likert scale) and global perceived effect (7-point Likert scale); (10) Patients are asked to report which study medicine they think they received (antibiotics/placebo/unsure); (11) Co-interventions (concomitant medication and non-pharmacological treatments) and sick-listing is monitored monthly also during the follow-up period (100 to 365 days) for health-economical calculations; (12) Embraces patients from two participating hospitals. At day 0, faeces are collected before the first tablet is administered; (13) Containers and capsules delivered to local ‘Sykehusapotek’ at each participating hospital for return capsule count, registering of accountability in electronic systems and destruction of the returned study drug