Black 1964.

Methods	Study design: randomised, double‐blind, cross‐over trial of methotrexate vs placebo Duration of study: minimum 80 days (20 days pretreatment; 60 days on treatment) Run‐in period: 20 days with trial dose of parenteral methotrexate to test for hypersensitivity Location: United States of America Number of study centres: 1 Study setting: inpatient Withdrawals: 1 ‐ method of handling missing data not described Dates of study: not reported
Participants	Randomised: n = 21 Completed: n = 20 Mean age: not reported Sex: 10 males; 11 females Mean disease duration: 8 years (dispersion measure not reported) Severity of condition: not reported Diagnostic criteria: rheumatologist‐diagnosed PsA Inclusion criteria: Adults aged 18 years or older Psoriasis and inflammatory joint disease of at least 1 year duration Exclusion criteria: Severe renal disease Severe liver disease Severe infection Haematological disorder (such as neutropaenia, severe anaemia, or thrombocytopaenia) Pregnancy
Interventions	Group AB: methotrexate intravenously or intramuscularly at progressively increasing doses from 1 to 3 mg/kg of body weight for the first treatment period, followed by parenteral placebo for the second treatment period Group BA: parenteral placebo first, followed by parenteral methotrexate as above for the second treatment period Concomitant medications: corticosteroid or salicylate therapy at the lowest dose that just allowed an increase in skin or joint activity Excluded medications: not reported
Outcomes	Time points: 60 days on one treatment, then cross‐over to the other treatment No extractable data. Study authors could not be contacted
Notes	Clinical trials registration: not reported Funding: not reported Declarations of interest: none reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"From the first bottle, either methotrexate or placebo according to a randomized schedule…" The schedule is not described in further detail
Allocation concealment (selection bias)	Unclear risk	This was not reported
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Double‐blind design, with infusions drawn from a vial No description was provided regarding the extent to which participants or personnel were blinded to treatment
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Due to lack of description of the extent of double‐blinding, risk of bias was judged 'uncertain'
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Handling of data from the 2 withdrawn participants (1 withdrawal, 1 death) was not clearly documented. As total study numbers are low, it is unclear if this might impact study outcomes
Selective reporting (reporting bias)	Unclear risk	This could not be substantiated, as no trial registry record was available for comparison
Other bias	Unclear risk	Compliance with therapy was largely complete (excluding the single withdrawal), and baseline characteristics were not relevant, as this study used a cross‐over design. However, the requirement for co‐intervention with corticosteroids and NSAIDs was variable, and it is unclear if this has had an impact on study outcomes