 9. Adhering to the following wash-out periods Topical treatment Wash-out Period Corticosteroids Vitamin A analogues Vitamin D analogues Anthracene derivatives Tar Salicylic acid preparations 2 weeks Systemic treatment Biologics with antipsoriatic activity 3 months Conventional systemic antipsoriatic drugs and phototherapy 1 month Immunosuppressive medication if not covered by any of the above treatments Cytostatics 6 months Medications with known harmful influences on the kidneys 5 x halftime 