Too slow inclusion rate.

The optimal therapeutic serum trough level (Ctrough) of adalimumab was defined between 3,5 and 7,0 µg/ml in patients with plaque type psoriasis. An adalimumab Ctrough above this therapeutic range did not add clinical response. Based on this therapeutic window, the introduction of dose adjustments based on Ctroughs (therapeutic drug monitoring) will be further validated in a prospective randomized-controlled trial. Here, we aim to determine whether, in patients with a good clinical response and supratherapeutic adalimumab Ctroughs, dose reduction is able to maintain favorable clinical outcome.

Patients will be included after signing informed consent and randomized in either a standard dose arm or a concentration based arm based on prior Ctrough measurements. In the concentration based arm, dosing frequency will be lowered to once every 3 weeks. If patients still have supratherapeutic Ctroughs of adalimumab, these patients will continue adalimumab self-administration every 4 weeks. In the standard based arm, patients will continue on standard dosing schedule. During each study visit blood will be taken in order to quantify Ctroughs. In addition, Psoriasis Area and Severity Index (PASI) and Investigator's Global Assessment (IGA) score will be evaluated by a physician. Patients complete the Dermatology Life Quality Index (DLQI) and European quality of life EQ-5D instrument at each visit. In addition, in a subset of patients in each treatment arm, additional sampling will be collected by dried blood spot sampling in order to build a PK(PD) model for adalimumab.

Inclusion Criteria:

1. Participants must have a clinical or histological diagnosis of chronic plaque-type psoriasis for at least 6 months prior to inclusion
2. Participants must have a stable disease during maintenance on adalimumab (absolute PASI < 3)
3. Participants are not allowed to use topical steroids from 7 days before randomization until the end of the study (week 48).
4. Participants must sign an ICF indicating that he or she understands the purpose of, and procedures required for, the study and is willing to participate in the study

Exclusion Criteria:

1. Participants who have currently a predominant nonplaque form of psoriasis
2. Participants who are pregnant, nursing or planning a pregnancy while enrolled in the study or within 12 weeks after receiving the last administration of study intervention
3. Participants who are unable or unwilling to undergo multiple venapunctures
4. Participants who are treated according to a different dosing schedule than standard dosing of adalimumab (regular dose regimen every 2 weeks; 40 mg)