Patients should follow the doctor's prescription exactly. Oral methoxsalen may be administered as a single dose with milk or after a meal, or in 2 divided doses approximately 30 minutes apart, to minimize adverse GI effects.
Idiopathic Vitiligo: Children > 12 years and Adults: Oral 20 mg daily 2 - 4 hours before exposure to UVA light or sunlight. Therapy should be on alternate days and never on 2 consecutive days. Oral dosages greater than 0.6 mg/kg should not be used, since severe burns may result.
Psoriasis: Adults: Oral 10 - 70 mg. 1.5-2 hours before exposure to UVA light. Treatments may be administered 2 or 3 times weekly (at least 48 hours apart) or as necessary. The initial dose of methoxsalen is based on the patient's body weight according to the following schedule: See table.
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The paint should be applied daily or less frequently according to the tolerance of the patient and should be used at least 1 hr before the ultraviolet or solar irradiation or at night a few minutes before sleep, to be followed in the morning by irradiation. The paint should be applied to the leucodermic patch or bald area by means of a cotton wad or brush.
Refrain from applying paint to delicate areas (eg, eyelids and genitalia). The treated parts must be exposed with measure to sunlight or if it is not possible, to ultraviolet light, during the period strictly prescribed by the physician. Do not exceed half a minute for the first time.
During treatment, local reactions may develop on the depigmented areas. The usual reaction is a more or less intense reddishness; blistering may be noted if the radiation has been prolonged too much. Should the reaction be excessive, it is then necessary to stop the painting for a few days until disappearance.
The treatment should be conducted under the supervision of a dermatologist. It has been observed clinically in the treatment of leucoderma that the best results are obtained by combining both oral and topical treatment together with solar or ultraviolet irradiation.