The trial is an open-label randomized study that will examine whether switching to a selective IL23 inhibitor (guselkumab) is more effective than switching to a second TNFi (golimumab) among patients with PsA who have an inadequate response to a TNFi.

The primary aim of the trial will be to determine, among psoriatic arthritis (PsA) patients with an inadequate response (IR) to a tumor necrosis factor inhibitor (TNFi), whether switching to a new mechanism of action (MOA), specifically guselkumab (GUS), a selective interleukin 23 inhibitor (IL23i) targeting the p19 subunit, is more effective than switching to another TNFi. The primary hypothesis of this study is that switching to a new MOA may be more effective than switching to a second TNFi. This will be the first trial to test such a switch in PsA patients. Additionally, the proposed study will address the effectiveness of a new therapy, GUS, in a clinical practice setting among patients who are TNF IR.

Inclusion Criteria:

1. Psoriatic arthritis meeting CASPAR criteria;
2. Active psoriatic arthritis defined by at least 1 swollen joint;
3. cDAPSA score ≥ 10; See also Exclusion #4 - cDAPSA must be > 14 in patients without psoriasis.
4. Using a TNFi or previously used a single TNFi historically and either never responded or lost response (TNF IR) and planning to switch to a new biologic therapy;
5. If using an oral small molecule/csDMARD (i.e., methotrexate, leflunomide, hydroxychloroquine, sulfasalazine, or apremilast), must be on a stable dose for 4 weeks and remain on a stable dose during the study; Use of up to two OSM/csDMARDs is allowed.
6. If using NSAIDs, glucocorticoids (<10 mg daily) or topical medications for psoriasis, must be on a stable dose for 4 weeks prior to Screening/Baseline 1 and remain on a stable dose during the study;
7. Age 18-80 (patients older than 80 may be more likely to have concomitant osteoarthritis which may make it difficult to assess whether symptoms are related to PsA vs OA).

Exclusion Criteria:

1. Prior exposure to golimumab or another non-TNFi biologic (IL12/23i, JAKi, an IL17i, or an IL23i); prior exposure to a TYK2i is acceptable, but cannot be used during course of the study;

2. An adverse event that precludes use of another TNFi (development of drug-induced SLE, allergic reaction, serious infection, heart failure symptoms, demyelination at any point during use of therapy) or any other contraindication or substantial intolerance to a TNFi;

3. Use of moderate to high dose glucocorticoids (>10 mg);

4. Already meets the primary endpoint at Baseline; [cDAPSA low disease activity ≤ 14; IGA of psoriasis 0/1] In patients with psoriasis, cDAPSA can be 10-14 IF the Investigator Global Assessment of Psoriasis ≥ 2.

   In patients without psoriasis, cDAPSA must be > 14 to meet eligibility requirements.

5. Currently pregnant or actively trying to conceive.