Lassus 1988.

Methods	Parallel‐arm trial Number of centres not stated Period of inclusion not stated
Participants	Inclusion criteria Not stated Exclusion criteria Kidney insufficiency Liver insufficiency Women of childbearing age not on contraceptives Systemic treatment used during the 4 weeks preceding the trial Uncontrolled cardiovascular disorders Participants were examined before treatment and at weeks 2, 4, 8, and 12 Baseline data: randomised to acitretin (n = 30) or etretinate (n = 30) Mean age (range), years: 49.9 (22 to 70); 52.9 (27 to 76) Male/female: 11/19; 7/23 Proportion of participants with psoriatic lesions elsewhere: not specified Withdrawal: 1 in the acitretin group (complete remission after week 4) and 1 in the etretinate group (failed to return for follow‐up visits)
Interventions	Intervention 1 A: acitretin (3 capsules of 10 mg each, once per day) (30 participants) Intervention 2 B: etretinate (3 capsules of 10 mg each, once per day) (30 participants) Co‐interventions: topical corticosteroids, oral antibiotics Duration of treatment: 12 weeks
Outcomes	No primary or secondary outcome pre‐specified ‐ Decrease in the number of fresh pustules ‐ Severity score depending on intensity of erythema, scaling, and infiltration (3 = severe, 2 = moderate, 1 = mild, 0 = none) ‐ Area of involvement ‐ Adverse events
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "patients were randomly allocated to one of the two retinoid treatment groups" Comment: insufficient information about the sequence generation process to permit judgement
Allocation concealment (selection bias)	Unclear risk	Quote: "patients were randomly allocated to one of the two retinoid treatment groups" Comment: no information on method to guarantee allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "double‐blind comparative trial" Comment: unlikely that blinding could have been broken because both treatments are retinoids and have identical side effects
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "double‐blind comparative trial" Comment: unlikely that blinding could have been broken because both treatments are retinoids and have identical side effects
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Two patients left the study before 12 weeks of treatment; one from the etretinate group failed to return for follow‐up visits after the week 2 check while the other patient, who belonged to the acitretin group, discontinued treatment because of complete remission after 4 weeks" Comment: 2 participants dropped out but unclear how study authors dealt with it, especially that the dropout in the acitretin group was cleared, whereas we have no precision regarding the dropout in the etretinate group
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results