Hattel 1974.

Methods	Randomised controlled trial with cross‐over One centre in Copenhagen Period of inclusion: year 1972
Participants	Inclusion criteria Palmoplantar pustulosis: yellowish sterile pustules on the palms and on the sole or sides of the heel Histologically, typical spongiosiform pustules of pustular psoriasis were absent Exclusion criteria Not stated Baseline data Not stated but typical psoriatic lesions were absent Withdrawal: no mention of missing data
Interventions	Intervention A: hydroxyurea 0.5 g thrice daily (13 participants, cross‐over design) Control Intervention B: placebo (13 participants, cross‐over design) Co‐interventions: none Duration of treatment: 3 weeks
Outcomes	No primary or secondary outcomes pre‐specified Total number of pustules Score (0 to 3): sum of 4 pustule scores and 4 redness‐thickness scores Side effects Photographs were taken before and after each 3‐week period
Notes	Hydrea was supplied by Squibb and Sons
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "randomised" Comment: insufficient information about the sequence generation process to permit judgement
Allocation concealment (selection bias)	Unclear risk	Comment: the method to guarantee allocation concealment is not described
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "double‐blind, cross‐over" Comment: use of placebo but insufficient information to permit judgement
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "double‐blind, cross‐over" Comment: use of placebo but insufficient information to permit judgement
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: no mention of missing data
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results