Nissilä 1978b.

Methods	Design: RCT Number of centres: 1 Treatment duration: 3 weeks Flare design: No Wash‐out period: Yes (3 to 4 days) Time point of assessments: BL, 7, 14, 21 days
Participants	Inclusion criteria: Definite diagnosis of AS. Exclusion criteria: 1. Previously known renal, liver or gastrointestinal disorders; 2. Intolerance to indomethacin. Classification: NA Proquazone (900 mg): Number of participants: 15 Number of completers: NA Age: NA Male (%): 93 Symptom duration: NA Disease duration: NA HLA‐B27 positive (%): NA Proquazone (900 mg): Number of participants: 15 Number of completers: NA Age: NA Male (%): 93 Symptom duration: NA Disease duration: NA HLA‐B27 positive (%): NA
Interventions	Proquazone (900 mg) vs Indomethacin (75 mg) Co‐medication: "An additional fourth capsule was taken 65 times (average 4.3 capsules/patient) in the proquazone group and 47 times (average 3.1 capsules/patient) in the indomethacin group."
Outcomes	Extracted outcomes: Withdrawals due to adverse events Number of any adverse events Number of adverse events per organ system
Notes	Two separate studies (Nissilä 1978a; Nissilä 1978b) were reported in one paper. Funding source: Not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No information is provided on sequence generation.
Allocation concealment (selection bias)	Unclear risk	No information provided on allocation concealment.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"The capsules used were identical in appearance." Study participants were adequately blinded to their allocated treatment.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	"two separate 3‐week clinical, double‐blind, randomized studies…" No further information is provided on blinding of outcome assessors.
Incomplete outcome data (attrition bias) All outcomes	Low risk	"A total of 56 patients out of 60 completed the study." Dropouts were low in both groups of both studies and equally distributed among all groups.
Selective reporting (reporting bias)	Low risk	All outcomes stated in the methods are reported.
Other bias	Unclear risk	"There was no significant difference between the groups regarding age, and duration of severity of the disease." No BL characteristics reported in the article, so BL characteristics imbalance cannot be determined other than this.