What it's for (Indications)
- Used in the treatment of psoriasis (especially severe, recalcitrant, disabling forms not adequately responsive to other treatments) and idiopathic vitiligo (skin condition characterized by white patches or loss of pigment from areas of skin).
Dosage Information
| Type | Guideline |
|---|---|
| Standard | Methoxsalen Capsules represent a new dosage form with significantly greater bioavailability and earlier photosensitization onset time compared to previous forms. Each patient should be evaluated by determining the minimum phototoxic dose (MPD) and phototoxic peak time after drug administration prior to initiating photochemotherapy. As a guideline for initial psoriasis therapy, Methoxsalen capsules should be taken 1-1/2 to 2 hours before UVA exposure with some low-fat food or milk, according to the following weight-based dosing schedule: - Patient's Weight: <30 kg (<66 lbs) - Dose: 10 mg - Patient's Weight: 30-50 kg (66-110 lbs) - Dose: 20 mg - Patient's Weight: 51-65 kg (112-143 lbs) - Dose: 30 mg - Patient's Weight: 66-80 kg (146-176 lbs) - Dose: 40 mg - Patient's Weight: 81-90 kg (179-198 lbs) - Dose: 50 mg - Patient's Weight: 91-115 kg (201-254 lbs) - Dose: 60 mg - Patient's Weight: >115 kg (>254 lbs) - Dose: 70 mg Geriatric patients should generally be started at the lower end of the dosage range. |
Safety & Warnings
Common Side Effects
- The most commonly reported side effects include nausea (which may be minimized by taking with milk/food or splitting the dose), pruritus (which may occur with combined Methoxsalen/UVA therapy and can often be alleviated with emollients; severe or intractable generalized pruritus may require discontinuation of UVA treatment), and mild, transient erythema (occurring 24-48 hours after PUVA therapy).
- Other reported adverse reactions include nervousness, insomnia, depression, edema (collection of body fluid in tissues and cavities), hypotension (low blood pressure), and vertigo (loss of balance).
- Patients experiencing any of these symptoms for a prolonged period should consult their doctor immediately.
Serious Warnings
- Black Box Warning: Methoxsalen with ultraviolet (UV) radiation should be used only by physicians who have special competence in the diagnosis and treatment of psoriasis and who have special training and experience in photochemotherapy. The use of Psoralen and ultraviolet radiation therapy should be under constant supervision of such a physician. For the treatment of patients with psoriasis, photochemotherapy should be restricted to patients with severe, recalcitrant, disabling psoriasis which is not adequately responsive to other forms of treatment.
- Protect eyes and skin against complementary sun exposure after controlled UV irradiation.
- Patients should be monitored for possible long-term risks of photo-chemotherapy, including skin aging, changes in pigmentation, and cataract formation.
- For pregnancy and lactation, please consult your doctor.
- Methoxsalen with ultraviolet (UV) radiation must be administered only by physicians with special competence in the diagnosis and treatment of psoriasis and who have specific training and experience in photochemotherapy; the therapy should be under constant supervision of such a physician.
- Caution is advised for aphakic patients due to a significantly increased risk of retinal damage.
How it Works (Mechanism of Action)
Methoxsalen is a potent photoactive furocoumarin derivative that exerts its therapeutic effects primarily through its ability to intercalate into deoxyribonucleic acid (DNA) upon activation by long-wave ultraviolet A (UVA) radiation, typically in the range of 320-400 nm. Following oral administration and systemic absorption, methoxsalen localizes within the nuclei of epidermal cells. When subsequently exposed to UVA light, the activated methoxsalen forms covalent monoadducts and diadducts, specifically cross-links, with the pyrimidine bases (thymine and cytosine) of DNA. These photo-induced DNA cross-links severely impair DNA replication, transcription, and repair mechanisms, leading to a significant inhibition of cell proliferation. In hyperproliferative skin disorders such as psoriasis, this action effectively reduces the rapid turnover of keratinocytes. Beyond its direct antiproliferative effects, methoxsalen also possesses immunomodulatory properties, influencing T-lymphocyte function, cytokine production, and the activity of epidermal Langerhans cells, further contributing to its therapeutic efficacy in various dermatological conditions. For vitiligo, its mechanism involves stimulating melanogenesis and potentially promoting melanocyte proliferation and migration, thereby aiding in repigmentation.