The mechanism by which calcitriol improves psoriasis is similar to Calcipotriol. Calcitriol (a.k.a. 1,25-Dihydroxycholecalciferol) is the active form of vitamin D, which regulates calcium absorption in the body.
Calcitrol suppresses the psoriatic symptoms by limiting skin cell proliferation. More specifically, it prevents the excessive production of keratinocytes (95% of the skin is made of keratinocytes) by inhibiting DNA synthesis (the process by which cells reproduce). Calcitriol also keeps T-cell reproduction under control (T-cell proliferation is believed to cause the swelling and scaling that characterize psoriasis). Calcitriol interacts with these cells by binding their vitamin D receptors, which then regulates their ability to reproduce.
Recent studies (such as this one) have demonstrated that calcitriol suppresses psoriasis to a similar degree as calcipotriol, though with less skin irritation, in particular to more sensitive areas such as the face. This would be good news for any patient who needs to administer this topical medication for years at a time. Psoriasis is (officially) incurable, so there some people may need to take psoriasis medications for the duration of their lives.
People with a history of calcium-related health issues (hypercalciuria, hypercalcemia or kidney stones) should not take calcitriol as this drug increases the body’s ability to retain calcium. For this reason calcitriol is also used to treat hypocalcemia and osteoporosis.
