Study	Reason for exclusion
Falagas 2008	Systematic review and meta‐analysis
Forstrom 1974	Not controlled
Gudjonsson 2003	No intervention, not randomised
Komine 2000	Not randomised
Kurwa 1973	Not randomised
Masood 1997	Only able to obtain abstract. We assumed this study was uncontrolled. The authors claimed that in 200 unselected psoriasis participants treated with phenoxymethylpenicillin, excellent responses were observed in guttate psoriasis (80% complete clearance), good responses in acute exacerbation of chronic psoriasis (50% clearance), and poor in chronic plaque psoriasis (10% clearance).
Nyfors 1973	Not randomised
Owen 2001	Review
Rappersberger 1996	Other treatment (topical immunosuppressive treatment)
Raza 2007	Not randomised
Rosenberg 1986	Case control study
Stutz 1996	Topical antibiotic
Tsankov 2011	Not randomised; this trial compared rifampicin to placebo in participants with guttate psoriasis; in one intervention group, participants were Streptococcus positive, and in the second intervention group, Streptococcus negative. There were up to 82 participants in the intervention group and only 10 in the placebo group.