From the Guidelines
Methoxsalen should be administered 1.5 hours before exposure to UVA, as recommended by the guidelines of care for the management of psoriasis and psoriatic arthritis 1.
Overview of Methoxsalen
Methoxsalen is a medication primarily used to treat skin conditions like psoriasis, vitiligo, and certain types of eczema. It belongs to a class of drugs called psoralens and works by increasing skin sensitivity to ultraviolet light.
Administration and Dosage
The standard administration timing is based on the guidelines, which state that oral PUVA with 8-methoxypsoralen should be administered 1.5 hours before exposure to UVA 1.
Treatment Regimens
Treatment regimens typically involve 2-3 sessions per week for several weeks or months. Patients must wear protective eyewear during and after treatment, avoid sun exposure for 24 hours following treatment, and use sunscreen to prevent severe burns.
Mechanism of Action and Side Effects
Methoxsalen works by intercalating with DNA and, when activated by UVA light, forms cross-links between DNA strands, which reduces rapid cell division in affected skin areas. Side effects may include nausea, itching, redness, and increased risk of skin cancer with long-term use, so regular skin examinations are recommended.
Important Considerations
It is essential to note that high cumulative exposure to oral PUVA is associated with a dose-related increase in the risk of nonmelanoma skin cancer, particularly SCC, as reported in a meta-analysis of several PUVA trials 1.
Key Recommendations
- Administer methoxsalen 1.5 hours before UVA exposure 1
- Use protective eyewear during and after treatment
- Avoid sun exposure for 24 hours following treatment
- Use sunscreen to prevent severe burns
- Regular skin examinations are recommended to monitor for side effects and skin cancer risk.
From the FDA Drug Label
Methoxsalen Soft Gelatin Capsules USP contains 10mg methoxsalen. The FDA drug label does not answer the question.
From the Research
Methoxsalen Overview
- Methoxsalen, a naturally occurring linear furocoumarin, has been used in combination with ultraviolet (UV) A irradiation to manage psoriasis and vitiligo 2.
- It causes a dose-related increase in cutaneous photosensitivity, but has lower photoactivity compared to 8-methoxypsoralen 2.
Efficacy in Psoriasis and Vitiligo
- Psoriasis clearance rates of > 90% or > 97% were observed in similar numbers of patients receiving oral PUVA 5-methoxypsoralen or oral PUVA 8-methoxypsoralen treatment 2.
- Up to 56% of patients with vitiligo achieved > 75% repigmentation with 5-methoxypsoralen combined with UV irradiation 2.
- A study comparing topical trichloroacetic acid 70% versus methoxsalen 0.2% paint in stable acral vitiligo found that both modalities did not demonstrate a significant clinical nor dermoscopic response 3.
Adverse Effects and Tolerability
- The incidence and severity of adverse events was generally lower in PUVA 5-methoxypsoralen recipients compared to PUVA 8-methoxypsoralen recipients 2.
- Nausea and/or vomiting, pruritus, and erythema were the most commonly reported adverse events in the short term, occurring less frequently in 5-methoxypsoralen recipients 2.
- Long-term tolerability data for PUVA 5-methoxypsoralen are scarce, but no carcinogenicity was reported during a 14-year observation period of 413 patients with psoriasis 2.
Combination Therapies
- Combination therapies, such as topical corticosteroids with excimer laser and UVA, seem to be more effective than steroids alone in treating vitiligo 4.
- Combinations of vitamin D analogues and calcineurin inhibitors with UV light have varied efficacy, depending on the type used and the type of UV light 4.