Comparison of the antipsoriatic effect and tolerability of calcipotriol-containing products in the treatment of psoriasis vulgaris using a modified psoriasis plaque test.

In 1972, Dumas and Scholtz developed the psoriasis plaque test to evaluate the potency of local corticosteroids. Through further modification of this method, the efficacy between antipsoriatic products can be differentiated. This method allowed for the simultaneous application of several products to different test sites in the same psoriasis patient. The objective of this current study was to compare the antipsoriatic effect of six topical products using a modified version of the original psoriasis plaque test with emphasis on the predictive capacity of this model. Validation of the use of immunohistochemical and histological scoring of biopsy material, in conjunction with clinical scoring, in the prediction of antipsoriatic effects was an additional objective. This study was a single-centre, investigator-blinded, within-subject randomized, active- and vehicle-controlled, intraindividual comparison of six topical products in patients with psoriasis vulgaris. The products evaluated were calcipotriol ointment (50 μg/g); calcipotriol cream (50 μg/g); two-compound ointment (calcipotriol 50 μg/g; betamethasone dipropionate 0.5 mg/g); two-compound gel (calcipotriol 50 μg/g; betamethasone dipropionate 0.5 mg/g) [all in their marketed formulations]; an investigational ointment (calcipotriol 25 μg/g; hydrocortisone 10 mg/g); and a vehicle control. Psoriasis patients (≥18 years of age; n = 24) received simultaneous topical application of each of the products 6 days a week for a period of 21 days, at different test sites located on psoriasis plaques. Clinical assessment of the test sites was completed twice a week. Test site biopsies were taken at the final visit for histological analysis. The primary endpoint was the absolute change in total clinical score (TCS; erythema, scaling and infiltration) from baseline. For all products, the change in TCS correlated well with changes in histological and immunohistochemical values. The two-compound ointment and the two-compound gel both resulted in a large and significant reduction in TCS. Calcipotriol ointment and the calcipotriol/hydrocortisone ointment were less effective, although they were still more effective than the calcipotriol cream and the ointment vehicle. This study has demonstrated that the modified psoriasis plaque test can provide a relatively quick and effective method to evaluate the antipsoriatic effect of several topical treatments in small cohorts and that, by combining clinical scoring and histological assessment, a more accurate prediction of the antipsoriatic effect can be made. The two-compound formulations (ointment and gel) had a comparable antipsoriatic effect, which was superior to the other products tested. Furthermore, these data indicate that the gel formulation could provide an alternative effective treatment option to the well established two-compound ointment for psoriasis patients. Registered as EudraCT no: 2007-005463-10.