(1997; 132 pages) [French] [Spanish]
Capsule, 10 mg
Methoxsalen (8-methoxypsoralen) is a psoralen derivative that occurs naturally in many plants but is prepared synthetically for therapeutic use. When exposed to ultraviolet A irradiation, it forms photochemical conjugates with nucleic acid that inhibit DNA replication.
It is readily absorbed after oral administration and serum levels peak 2-3 hours after ingestion. The drug is rapidly and extensively metabolized and is excreted in the urine.
Treatment of severe psoriasis refractory to topical therapy in conjunction with controlled exposure to ultraviolet A radiation (PUVA therapy).
Dosage and administration
Adults and children over 12 years: 0.3-0.4 mg/kg administered 2 hours before exposure to ultraviolet A radiation. Between 12 and 24 sessions are usually necessary. The sessions should be given twice or three times weekly (at least 48 hours apart).
• Hypersensitivity to psoralens.
• Pre-existing diseases associated with photosensitivity including porphyria, acute systemic lupus erythematosus and hydroa vacciniforme.
• Age under 12 years.
Treatment should be administered only under the supervision of a physician with special training in photo-chemotherapy.
Protective sunglasses should be worn during therapy and for the following 24 hours in order to avoid the risk of cataract formation.
Patients must be advised to avoid exposure to sunlight for at least 8 hours after therapy.
Gastric discomfort occasionally occurs.
Cheilitis and transient loss of muscle coordination have been reported. Exposure to ultraviolet radiation after methoxsalen therapy may induce a small degree of pigmentation. PUVA therapy carries an increased risk of cutaneous carcinoma in patients with predisposing factors.
Overdosage of methoxsalen or over-exposure to ultraviolet light following methoxsalen administration can result in severe burning and blistering of the skin. The patient should be placed in a darkened room for at least 24 hours or until the cutaneous reaction has subsided, and supportive measures for the treatment of burns should be initiated.
Induction of emesis or gastric lavage is of value when undertaken within a few hours of ingestion.
Capsules should be stored in well-closed containers, protected from light.