Psoriasis affects more than 7 million Americans. Plaque-type psoriasis (the most common type of psoriasis) is an inflammatory skin condition with reactive abnormal epidermal differentiation and hyperproliferation. It is characterized by raised, thickened, plaques of erythematous skin covered by a silvery-white scale. Plaque-type psoriasis is most commonly found on the knees, elbows, and scalp but can appear anywhere on the body. While patients with psoriasis may complain of itchiness and discomfort, the psychological effects of the disease are the most debilitating. In a 1998 survey conducted by the National Psoriasis Foundation, it was found that 79% of the psoriasis patients surveyed reported that the disease had a negative impact on their lives and 40% felt frustrated with the ineffectiveness of their current therapies.~Although the exact cause of this skin disease is unknown, it is clear that immune-based inflammatory mechanisms initiate an accelerated growth of skin cells. This accelerated growth results in an agglomeration of skin cells on the surface of the epidermis that the body cannot shed. This agglomeration creates the thickened patches of scaly skin characteristic of the disease.~Clinical use of systemic vitamin D to treat psoriasis has been limited because of the induction of hypercalcemia. In contrast, low doses of topically administered vitamin D analogs have been shown to have an anti-psoriatic effect without the risk of hypercalcemia. Topical vitamin D analogs have the ability to inhibit the proliferation and promote the differentiation of keratinocytes in psoriatic skin. In addition, vitamin D analogs may also act by inhibiting cytokine production by keratinocytes or lymphocytes. Calcipotriol, the most thoroughly studied of the vitamin D analogs, was first approved in Europe in the early 1990s. It has been shown to be comparable or slightly more effective than class II corticosteroid ointments. In patients with extensive psoriasis, calcipotriol ointment was shown to be effective. However, patients had reduced levels of parathyroid hormone; mean serum and urine calcium were increased during treatment and hypercalciuria was recorded in 3 patients. These effects were reversible with discontinuation of therapy. In a review of the effects on calcium homeostasis, it was noted that calcipotriol (50 µg/g) had no effects on serum or urine calcium when administered at doses of 40-50 g/week and two reports of hypercalcemia at doses of 70-100 g/week. Thus, while calcipotriol ointment was shown to be effective, the potential for alterations in calcium homeostasis have limited its use to 100 g of ointment per week (0.5 mg calcipotriol/week). Subsequently, calcipotriol and tacalcitol, another vitamin D analog, have become first-line therapies in the management of mild to moderate psoriasis in several countries in Western Europe, Japan and the USA.~Work has continued on the creation of new vitamin D analogs, such as COL-121, with the intent of eliminating the adverse effects of hypercalcemia and hypercalciuria with a compound that is more stable and more easily administered.
Low doses of topically administered vitamin D analogs have been shown to have an anti-psoriatic effect without the risk of hypercalcemia. Calcipotriol, the most thoroughly studied of the vitamin D analogs, was first approved in Europe in the early 1990s. It has been shown to be comparable or slightly more effective than class II corticosteroid ointments. However, patients had reduced levels of parathyroid hormone; mean serum and urine calcium were increased during treatment and hypercalciuria was observed. These effects were reversible with discontinuation of therapy. Thus, while calcipotriol ointment was shown to be effective, the potential for alterations in calcium homeostasis have limited its use to 100 g of ointment per week (0.5 mg calcipotriol/week). Work has continued on the creation of new vitamin D analogs, such as COL-121, with the intent of eliminating the adverse effects of hypercalcemia and hypercalciuria with a compound that is more stable and more easily administered.