Topical calcitriol – studies on local tolerance and systemic safety

Calcitriol 3 μg g⁻¹ ointment (Silkis ointment®, Galderma Laboratories) is a new treatment for psoriasis. Calcitriol is the biologically active metabolite of vitamin D₃. It induces keratinocyte differentiation, inhibits keratinocyte, T-cell and fibroblast proliferation, and inhibits the production of some inflammatory mediators, all contributors to the pathogenesis of psoriasis. Preclinical studies have shown an effect of topical calcitriol on calcium homeostasis at doses higher than those in clinical use. No adverse local events were observed when calcitriol was applied to animal skin. Phase I clinical studies confirmed that calcitriol 3 μg g⁻¹ ointment is well tolerated in humans. These studies have demonstrated that at the minimal effective concentration of 3 μg g⁻¹, calcitriol ointment has no discernible photosensitizing or phototoxic potential and no skin irritant or allergic potential in healthy volunteers. Its low systemic absorption through human skin is unlikely to significantly affect calcium homeostasis. This paper summarizes the findings of the preclinical and early clinical studies that provided the foundation of the later Phase II and III clinical trials on efficacy and safety with topical calcitriol 3 μg g⁻¹ ointment for the treatment of plaque psoriasis.