Cost–utility analysis of antibiotic treatment in patients with chronic low back pain and Modic changes: results from a randomised, placebo-controlled trial in Norway (the AIM study)

Abstract

Objective: To evaluate the cost–utility of 100 days of antibiotics in patients with chronic low back pain (LBP) and type I or II Modic changes included in the Antibiotic treatment In patients with chronic low back pain and Modic changes (AIM) study. Design: A cost–utility analysis from a societal and healthcare perspective alongside a double- blinded, parallel group, placebo, multicentre trial. Setting: Hospital outpatient clinics at six hospitals in Norway. The main results from the AIM study showed a small effect in back- related disability in favour of the antibiotics group, and slightly larger in those with type I Modic changes, but this effect was below the pre- defined threshold for clinically relevant effect. Participants: 180 patients with chronic LBP, previous disc herniation and Modic changes type I (n=118) or type II (n=62) were randomised to antibiotic treatment (n=89) or placebo- control (n=91). Interventions: Oral treatment with either 750 mg amoxicillin or placebo three times daily for 100 days. Main outcome measures: Quality- adjusted life years (QALYs) by EuroQoL- 5D over 12 months and costs for healthcare and productivity loss measured in Euro (€1=NOK 10), in the intention- to- treat population. Cost– utility was expressed in incremental cost- effectiveness ratio (ICER). Results: Mean (SD) total cost was €21 046 (20 105) in the amoxicillin group and €19 076 (19 356) in the placebo group, mean difference €1970 (95% CI; −3835 to 7774). Cost per QALY gained was €24 625. In those with type I Modic changes, the amoxicillin group had higher healthcare consumption than the placebo group, resulting in €39 425 per QALY gained. Given these ICERs and a willingness- to- pay threshold of €27 500 (NOK 275 000), the probability of amoxicillin being cost- effective was 51%. Even when the willingness- to- pay threshold increased to €55 000, the probability of amoxicillin being cost- effective was never higher than 53%. Conclusions: Amoxicillin treatment showed no evidence of being cost- effective for people with chronic LBP and Modic changes during 1- year follow- up.