Comparing the effectiveness of tofacitinib extended release (XR) chronotherapy, morning versus evening dosing, in rheumatoid arthritis (RA) and psoriatic arthritis (PsA) patients from a patient's, clinical as well as a translational point of view.

Prior treatment

• Current or previous treatment of arthritis with tsDMARD(s)

Lab values

• (Relative) contraindications for study medication:a. Evidence of ongoing infectious or malignant process obtained within 3 months prior to screening and evaluated by a qualified health care professional. b. Pregnant or nursing (lactating) women. c. Female participants of child bearing potential and male participants whose partner is of child bearing potential who are not willing to ensure that they or their partner use effective contraception during the trial and for 3 months thereafter as in standard practice. d. History of clinically significant liver disease or liver injury as indicated by abnormal liver function tests (LFT) such as aspartate aminotransferase/serum glutamic oxaloacetic transaminase (AST/SGOT), alanine aminotransferase/ serum glutamic pyruvic transaminase (ALT/SGPT), alkaline phosphatase, or serum bilirubin. The Investigator should be guided by the following criteria: Any single parameter may not exceed 2 x upper limit of normal (ULN). A single parameter elevated up to and including 2 x ULN should be re-checked once more as soon as possible, and in all cases, at least prior to enrolment/randomization, to rule out laboratory error. e. History of renal trauma, glomerulonephritis, or subjects with one kidney only, or a glomerular filtration rate (GFR) < 30 ml/min. f. Other underlying metabolic, hematologic, renal, hepatic, pulmonary, neurologic, endocrine, cardiac, infectious or gastrointestinal conditions which in the opinion of the Investigator immunocompromises the patient and/or places the patient at unacceptable risk for participation in an immunomodulatory therapy. g. Use of powerful CYP3A4 inhibitors (e.g. ketoconazole, fluconazole, tacrolimus and ciclosporin)

Other

• Prednisone (or equivalent) usage at a dose of >7.5mg
• Work in shifts
• Unable to understand, speak and write in Dutch.

• RA or PsA, , according to respectively the ACR/EULAR 2010 criteria for RA and CASPAR criteria
• Active disease, respectively defined as a DAS>2.4 or DAPSA>14
• Age ≥18 years