[The irritant effect of dithranol using capillary resistance measurement]

Area of Science:

• Dermatology
• Pharmacology

Context:

• Psoriasis patients exhibit lower baseline capillary resistance (CR) compared to healthy individuals.
• Topical dithranol is a common psoriasis treatment with known irritant effects.
• Understanding dithranol's impact on microcirculation is crucial for optimizing treatment and minimizing side effects.

Purpose:

• To investigate the effect of topical dithranol on capillary resistance (CR) in healthy volunteers and psoriatic skin.
• To determine if pre-treatment with antihistamines or cyclooxygenase inhibitors can prevent dithranol-induced CR reduction.
• To assess the impact of coal tar addition on dithranol's effect on CR.

Summary:

• Topical dithranol (0.10% and 0.25%) significantly decreased capillary resistance in both healthy and psoriatic skin.
• Pre-administration of clemastine (antihistamine) or indomethacin (cyclooxygenase inhibitor) prevented or reduced this decrease.
• Adding 5% coal tar to dithranol preparations also moderated the reduction in CR.

Impact:

• Dithranol's irritant effect on skin microvasculature is mediated, in part, by histamine and prostaglandins.
• These findings suggest potential strategies to mitigate dithranol-induced skin irritation during psoriasis treatment.
• The study highlights the importance of considering co-treatments or formulation modifications to improve dithranol tolerability.