OBJECTIVES: To investigate the association between tobacco smoking and disease activity, treatment adherence and treatment responses in patients with AS treated with their first tumour necrosis factor-alpha inhibitor (TNFi) therapy in routine care.

METHODS: Observational cohort study based on the Danish nationwide DANBIO registry. Kaplan-Meier plots, Cox and logistic regression analyses by smoking status (current/never/previous) were calculated for treatment adherence and BASDAI 50%/20 mm-response. Additional stratified analyses were performed for gender and TNFi-type.

RESULTS: Of 1576 AS patients included in the study, 1425(90%) had known smoking status (current/never/previous: 43%/41%/16%). The median follow-up time was 2.02 years (IQR 0.69-5.01). At baseline, current smokers compared with never smokers had longer disease duration (4 years (1-12)/2 years (0-10)), higher BASDAI (61 mm (47-73)/58 mm (44-70)), BASFI (53 mm (35-69)/46 mm (31-66)) and BASMI (40 mm (20-60)/30 mm (10-50)) scores (all P < 0.01). Current and previous smokers had shorter treatment adherence than never smokers (current: 2.30 years (1.81-2.79) (median (95% CI)); previous: 2.48 years (1.56-3.40), never: 4.12 years (3.29-4.95)), P < 0.0001). Similar results were found in multivariate analyses (current versus never smokers, HR 1.41 (95% CI 1.21-1.65), P < 0.001), most pronounced among men. Current smokers had poorer 6 months' BASDAI50%/20 mm-response rate than never smokers (42%/58%, P < 0.001). In multivariate analyses, current smokers had lower odds of achieving BASDAI50%/20 mm-response than never smokers, both overall (OR 0.48 (95% CI 0.35-0.65), P < 0.0001) and for the different TNFi-types (adalimumab 0.45 (0.27-0.76)/etanercept 0.24 (0.10-0.61)/infliximab 0.57 (0.34-0.95)).

CONCLUSION: In this study of TNFi-treated AS patients in clinical practice, current and previous smokers had significantly poorer patient-reported outcomes at baseline, shorter treatment adherence and poorer treatment response compared with never smokers.