Thomsen 1973.

Methods	Cross‐over trial Number of centres not stated Period of inclusion not stated
Participants	Inclusion criteria Affected palms and soles with crops of pustules with scaling and redness, accompanied by itching and tenderness Exclusion criteria Not stated Baseline data: tetracycline 250 mg twice daily vs placebo (n = 40) Mean age (range), years: 45.7 (16 to 78) Male/female: 8/32 Mean duration of disease (range), years: 4.7 (0.25 to 50 years) Proportion of participants with psoriatic lesions elsewhere: 12/40 Withdrawal: 2 participants stopped taking treatment after 2 courses because of side effects
Interventions	Intervention 1 A: tetracycline 250 mg twice daily (40 participants, cross‐over design) Intervention 2 B: placebo twice daily (40 participants, cross‐over design) Co‐interventions: none Duration of treatment: 12 weeks
Outcomes	No primary or secondary outcome pre‐specified Clearance of lesions with no pustules
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The treatment was randomised in three periods of 4 weeks each. Thus, each patient had one course of tetracycline and two courses of placebo or vice versa. The treatment periods followed immediately upon each other, but the sequence was accidental" Comment: unclear how randomisation was done
Allocation concealment (selection bias)	Unclear risk	Comment: no information on method to guarantee allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "double blind technique was applied. Tetracycline, 250 mg, and identical‐looking lactose capsules were used, the dosage being one capsule twice daily" Comment: we consider blinding at low risk for trial vs placebo with no obvious clinical adverse events or known specific taste of experimental drug
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "double blind technique was applied" Comment: we consider blinding at low risk for trial vs placebo with no obvious clinical adverse events or known specific taste of experimental drug
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "Of the forty patients treated thirty‐eight completed the study. Two patients stopped taking the drug after two courses because of side effects. Nevertheless, these two patients are included in the analysis" Comment: the 2 dropouts were included in the statistical analysis
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results