This study was conducted at our emergency department between June 2018 and March 2020 after receiving approval from our institutions' ethics committee (2018/1330). This study was registered as a randomized controlled trial with the US National Institute of Health (clinical trials.gov). We conducted a three-arm, prospective randomized open label clinical trial to compare isolated NSAID group, NSAID with paracetamol group and NSAID with oral magnesium supplementation group (described below) for treatment of acute LBP. Patients were included after providing informed consent predicated on their understanding of expected complications and treatment outcomes. Consolidate Standards of Reporting Trials (CONSORT) guidelines were followed reporting the results of the study Patients from a single university hospital were recruited for this study between June 2018 and March 2020. Inclusion criteria were defined as (1) age\>18 years old, (2) duration of symptoms \<2 weeks and (3) functionally impairing LBP which we defined as a score of \> 5 on Roland-Morris Disability Questionnaire (RMDQ).

Exclusion criteria included (1) age\>65 years old, (2) history of trauma, (3) presence of radicular pain physical examination which was defined as pain radiating below the gluteal folds, (4) history of primary vertebral tumor or metastasis, (4) patients who were pregnant or lactating, (5) presence of any contraindication or allergy to investigational medications, (6) history of chronic analgesic use, (7) history of autoimmune diseases or inflammatory rheumatic disorders, (8) history of cardiopulmonary restrictions, severe kidney or liver function disorders and (9) history of prior surgery of lumbar spine.

We based our sample size calculation assumptions on a recently published clinical trial \[11\] and widely accepted minimum clinically important improvement of 5 points on the RMDQ.(14) With alpha and beta values were set at 0.05 and 0.20 respectively, sample size calculation revealed that 50 patients were needed in each study group. To account for protocol violations, lost-to-follow-up and to ensure sufficient power for the intention to treat analysis (in previous work, up to 1/3 of enrolled patients did not use the investigational medication), we enrolled 80 patients for each group.

A computer generated random list was established with an online sequencer (www.random.org/sequences) according to which participants were randomly assigned to one of three study groups with 1:1:1 allocation ratio. Group A included isolated NSAID treatment and received 400 mg etodolac twice a day. Group B included NSAID and magnesium treatment and received a combination of 400 mg etodolac twice a day with 365 mg oral magnesium supplementation once a day. Group C included NSAID and paracetamol treatment and combination of 400 mg etodolac twice a day with 500 mg paracetamol twice a day was administered to the participants of this group (Figure-1). We effort to prevent the placebo effect by comparing the NSAID + magnesium therapy with both a NSAID plus paracetamol therapy and an isolated NSAID therapy. Treatment was performed by two authors (S.B and K.Ş) and patients were followed-up by same authors throughout the study. External medication was not allowed with the exception of topical analgesics. Patients who received any intravenous or intramuscular analgesia during the treatment period were excluded from study. Co-medications for any accompanying chronic condition (diabetes, hypertension etc.) were unchanged.

Clinical evaluation of participants was performed at first admission to emergency department, at 4th and 10th days after the initiation of designated treatment. Outcome measures included pain, mobility of lumbar spine and functional outcome. Pain intensity was assessed using a visual analogue scale (VAS). Lumbar spine mobility was assessed using the "finger to floor" test. Participants were asked to stand on erect posture with knees extended and then to bend forward in an attempt to reach for the floor with their fingertips without losing knee extension. Distance between patient's fingertips and the floor was then measured with a measuring tape. Functional outcome was evaluated with Roland-Morris Disability Questionnaire (RMDQ) score. RMDQ is a 24-item LBP functional scale and is recommended for research purposes. Higher scores signify greater low back-related functional impairment. An improvement of 5 points was considered clinically significant.