The calcipotriol dose–irritation relationship: 48 hour occlusive testing in healthy volunteers using Finn Chambers®

Calcipotriol is widely used in the treatment of psoriasis. Adverse lesional and perilesional irritation may occur. Allergy may occasionally be suspected. Allergy patch testing with calcipotriol may be difficult or impossible because calcipotriol is a local irritant. The aim of the present study was to assess the calcipotriol dose-irritation relationship, and establish a non-irritant patch test concentration for calcipotriol allergy patch testing. The study was a prospective, double-blind, randomized, dose titration evaluation in 180 healthy volunteers never previously exposed to calcipotriol. All individuals were patch tested with a calcipotriol dilution series (range 0.016-250 micrograms/mL). Clinical reading of test sites and measurement of erythema using a Minolta ChromaMeter were performed on days 2 and 3. Laser Doppler perfusion imaging of cutaneous blood flow was performed on day 3. Doubtful reactions (score 1/2) and weak reactions (score 1) were frequent and observed even at low dose exposure. Reactions declined in strength between the readings on day 2 and day 3. Only score 2 reactions with moderate erythema and some infiltration showed a threshold of no irritation. This threshold was confirmed by colorimetry and flowmetry. Cases of suspected allergy to calcipotriol may to avoid irritant reaction and false positive readings, be patch tested with calcipotriol 2 micrograms/mL citrate-buffered isopropanol solution applied under occlusion for 48 h using small Finn Chambers. Score 1/2 and 1 reactions are likely to reflect irritation. A positive test should be repeated after a minimum period of 3 months to ensure its consistency over time. A repeated open application test may be indicated.