Methoxasalen

Indications
 Oral
Repigmentation of vitiliginous areas
Adult: 20 mg or up to 600 mcg/kg 2-4 hr before measured periods of sunlight or UVA exposure depending on the preparation. Treatment is usually given twice a wk or on alternate days, with at least 48-hr intervals.
Child: >12 yr: 20 mg or up to 600 mcg/kg 2-4 hr before measured periods of sunlight or UVA exposure depending on the preparation. Treatment is usually given twice a wk on alternate days, with at least 48-hr intervals.
Oral
Psoriasis
Adult: Up to 600 mcg/kg 1.5-3 hr before UVA exposure, depending on the preparation. Treatment is usually given twice a wk or increased as necessary, with at least 48-hr intervals between doses. If there is no or minimal response after the 15th PUVA treatment, dose may be increased by 10 mg and this dose used for the remainder of the treatment course.
Topical/Cutaneous
Severe psoriasis
Adult: Apply a 0.15% preparation (or diluted to 0.015%) if necessary onto affected skin areas 15 min before UVA exposure. Alternatively, patient may take a whole body bath in methoxsalen solution (2.6 mg/l or up to 3.7 mg/l) followed by immediate UVA exposure. For treating affected areas, immerse the affected areas for 15 min into 3 mg/l solution of hand and foot soaks followed by a 30-min delay before UVA exposure twice a wk.
Topical/Cutaneous
Repigmentation of vitiliginous areas
Adult: Apply a 1% solution which is usually diluted to 0.1-0.01% (to avoid adverse effects) to the lesions; expose to UVA immediately after application or wait up to 2 hr. Area surrounding the lesion should be protected with a sunscreen. Wash and protect lesions from light after treatment; protection may be up to ≥48 hr. Treatment is usually repeated once a wk. Substantial repigmentation usually requires 6-9 mth of treatment.
Contraindications
 Diseases associated with light sensitivity e.g. porphyria. Aphakia, melanoma or a history of melanoma, invasive squamous cell carcinoma. PUVA therapy in children.
Warnings / Precautions
 Certain photosensitivity disorders. Hepatic impairment. Do not sunbathe for 24 hr before and 48 hr after PUVA treatment. Avoid exposure to sunlight for at least 8 hr after admin and patient should wear wrap-around UVA absorbing glasses for 24 hr after admin. Shield male genitalia during PUVA therapy unless specific treatment is required. Perform ophthalmic exam prior to therapy and at regular intervals thereafter, especially in those at increased risk of cataracts. Regularly examine patients for signs of premalignant or malignant skin lesions. Pregnancy and lactation.
Adverse Reactions
 Nausea, insomnia, depression, nervousness. Photochemotherapy or PUVA may cause pruritus, mild transient erythema, oedema, dizziness, headache, vesiculation, bulla formation, acneiform eruption, severe skin pain; pigmentation alterations of skin or nails, onycholysis. Hypersensitivity reactions e.g. fever, bronchoconstriction, contact dermatitis.
Potentially Fatal: Increased risk of skin cancers e.g. squamous cell carcinoma, basal cell carcinoma, malignant melanoma. Isolated reports of leukaemia.
Overdose Reactions
 Symptoms: Nausea and severe burns. Management: In acute oral intoxication, induction of emesis is beneficial within the first 2-3 hr of ingestion. Follow accepted treatment of severe burns. Keep room darkened until reaction subsides (≥8-24 hr).
Drug Interactions
 Additive effects with drugs known to cause photosensitisation e.g. anthralin, coal tar or derivatives, griseofulvin, phenothiazines, nalidixic acid, sulfonamides., tetracyclines and thiazide diuretics. May increase the levels/effects of aminophylline, fluvoxamine, mexiletine, mirtazapine, ropinirole, theophylline, trifluoperazine, dexmedetomidine and ifosfamide.
See Below for More methoxsalen Drug Interactions
Food Interactions
 Food containing photosensitisers e.g. figs, limes, parsley, mustard, carrots, cloves, lemon, celery may potentiate its effects. Absorption and serum concentrations appear to increase with food.
Mechanism of Actions
 Methoxsalen increases skin reactivity to long-wavelength UV rays. It bonds covalently to DNA inhibiting DNA synthesis and cell division, which can lead to cell injury. This effect is used in photochemotherapy or PUVA [psoralen (P) and high-intensity long-wavelength UVA irradiation].
Onset: 1 hr (depending on oral formulation).
Duration: About 8 hr.
Absorption: Well but variably absorbed from the GI tract (oral); peak plasma concentrations after 1-4 hr.
Distribution: Reversibly and highly bound to albumin; taken up by epidermal cells; diffuses into eye lens.
Metabolism: Hepatic; converted to metabolites.
Excretion: Via urine (about 95%, as metabolites).
Administration
 Should be taken with food.
ATC Classification
 D05AD02 - methoxsalen ; Belongs to the class of topical psoralens used in the treatment of psoriasis.
D05BA02 - methoxsalen ; Belongs to the class of systemic psoralens used in the treatment of psoriasis.
Available As
  • Methoxasalen 0.75% w/w
  • Methoxasalen 1%
  • Methoxasalen 1% w/v
  • Methoxasalen 10 mg
  • Methoxasalen 20 mg
  • Methoxasalen 50 mg

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