Vitamin D and systemic therapy.

The most frequently used systemic treatments for severe psoriasis are methotrexate (MTX), oral retinoids, and cyclosporine; however, all of these agents are associated with dose-related toxicities that limit their use. The safety and efficacy of topical calcipotriene for the treatment of psoriasis have been demonstrated in numerous clinical studies. The rationale for using calcipotriene in combination with systemic therapies is based on their different modes of action and nonoverlapping side effects. Three controlled clinical trials have demonstrated that the addition of calcipotriene ointment to systemic antipsoriatic treatment with MTX, acitretin, and cyclosporine increases the therapeutic efficacy compared with systemic therapy alone and minimizes side effects by either reducing the dosage or duration of treatment.