BackgroundThe influence of sex on treatment outcomes during interleukin-12/23 therapy in patients with psoriatic arthritis (PsA) has not been explored.ObjectiveTo conduct exploratory post hoc analyses of sex-stratified data from the MUST trial, an investigator-initiated, multicentre, phase 3b study in which patients with active PsA initiating treatment with open-label ustekinumab were randomised to treatment with placebo or methotrexate (MTX).MethodsWe evaluated baseline characteristics, key treatment outcomes and adverse events stratified by sex, with a focus on outcomes that did not include erythrocyte sedimentation rate (ESR) as a component due to the known elevation of ESR in females.ResultsA total of 166 patients were treated with ustekinumab+MTX (37 female, 50 male) or ustekinumab+placebo (32 female, 47 male). At baseline, females had a significantly longer time since PsA diagnosis and greater impairment in physical function, but similar joint counts. At week 24, both females and males showed marked improvements to ustekinumab with or without MTX. Females generally had numerically reduced treatment responses compared with males, although differences did not achieve statistical significance. MTX did not show an overall effect on treatment outcomes, but was associated with faster enthesitis responses in males only. Adverse events were generally comparable, but females in the ustekinumab+MTX group had higher levels of gastrointestinal disorders.ConclusionFemales and males with PsA had differences in baseline characteristics, treatment responses and adverse events during therapy. A better understanding of sex-based differences in PsA may help optimise treatment.