A Cochrane review included one trial with 20 subjects who had psoriasis, mainly guttate type, and evidence of beta-haemolytic streprococcal colonisation. Either rifampicin or placebo was added to the end of a standard course of antistreptococcal antibiotic (phenoxymethylpenicillin or erythromycin). No patient in either arm of the study improved during the observation period.
Comment: The quality of evidence is downgraded by very sparse data and indirectness of evidence (the patients had already been treated by standard antibiotic).