Methoxsalen


Concise Prescribing Info
Indications/Uses
Listed in Dosage.
Dosage/Direction for Use
Adult : PO Repigmentation of vitiliginous areas 20 mg or up to 600 mcg/kg 2-4 hr before measured periods of UVA exposure, given twice wkly or on alternate days, w/ at least 48-hr intervals. Psoriasis Up to approx 600 mcg/kg, 1.5-3 hr before UVA exposure twice wkly or increased as necessary, w/ at least 48-hr intervals between doses; may increase to 10 mg if no or minimal response after the 15th PUVA treatment. Topical Repigmentation of vitiliginous areas As 1% soln (diluted to 0.1-0.01%): Apply over lesions then expose to UVA immediately after application or wait up to 2 hr; repeat once wkly. Substantial repigmentation usually requires 6-9 mth of treatment. Psoriasis As a 0.15% soln (diluted to 0.015%, if necessary): Apply to affected areas 15 min before UVA exposure. Hand/foot soaks: Immerse the affected areas for 15 min into 3 mg/L soln followed by a 30-min delay before UVA exposure twice wkly.
Dosage Details
Oral
Repigmentation of vitiliginous areas
Adult: 20 mg or up to 600 mcg/kg 2-4 hr before measured periods of UVA exposure depending on the preparation, given twice wkly or on alternate days, w/ at least 48-hr intervals.

Oral
Psoriasis
Adult: Up to approx 600 mcg/kg, given 1.5-3 hr before UVA exposure, depending on the preparation. Treatment is usually given twice wkly or increased as necessary, w/ 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
Psoriasis
Adult: As a 0.15% soln (diluted to 0.015%, if necessary): Apply to affected areas 15 min before UVA exposure. Alternatively, patient may take a whole body bath in methoxsalen soln for 15 min followed by immediate UVA exposure. For treating affected areas, immerse the affected areas for 15 min into 3 mg/L soln of hand and foot soaks followed by a 30-min delay before UVA exposure. Baths or soaks are given twice wkly.

Topical/Cutaneous
Repigmentation of vitiliginous areas
Adult: As 1% soln (diluted to 0.1-0.01%): Apply over lesions then expose to UVA immediately after application or wait up to 2 hr. Protect the area surrounding the lesion w/ a sunscreen. Wash and protect lesions from light after treatment; protection may be up to ≥48 hr. Treatment is usually repeated once wkly. Substantial repigmentation usually requires 6-9 mth of treatment.
Administration
Should be taken with food.
Contraindications
Aphakia, existing or history of melanoma, invasive squamous cell carcinoma, photosensitivity diseases (e.g. porphyria, acute lupus erythematosus, xeroderma pigmentosum).
Special Precautions
Patient exhibiting multiple basal cell carcinoma or history of basal cell carcinoma, previous arsenic therapy, previous x-ray or grenz ray therapy; cardiac diseases or those unable to tolerate prolonged standing or exposure to heat stress; GI diseases or chronic infection. Hepatic impairment. Pregnancy and lactation.
Adverse Reactions
Oral: Nausea, insomnia, nervousness, depression. Photochemotherapy or PUVA: Mild transient erythema, pruritus; dizziness, headache, oedema, vesiculation, acneform eruption, bulla formation, severe skin pain, altered skin or nail pigmentation, onycholysis, premature skin ageing, severe burns, hypertrichosis.
Potentially Fatal: Increased risk of malignant cutaneous neoplasms.
Patient Counseling Information
Keep the treated areas protected from light by use of protective clothing or sunscreen.
MonitoringParameters
Conduct CBC w/ differential; liver and renal function, antinuclear antibody tests (at baseline and 6-12 mthly); ophth exam (pre-treatment and yrly); signs/symptoms of skin cancer, burns, photosensitivity.
Overdosage
Symptoms: Severe burning and blistering of skin. Management: Oral: Supportive treatment. Induce emesis w/in 2-3 hr after ingestion. Place the patient in a darkened room for at least 24 hr or until cutaneous reactions subside.
Drug Interactions
May increase plasma concentration of drugs metabolised by CYP2A6 isoenzyme. Additive effect w/ other systemic or topical photosensitising agents (e.g. anthralin, coal tar, nalidixic acid).
Food Interaction
Increased risk of phototoxicity w/ food that contain psoralens (e.g. parsley, parsnip, celery). Increased serum concentrations w/ food.
Action
Description: Methoxsalen increases skin reactivity to long-wavelength UV rays. It bonds covalently to deoxyribonucleic acid (DNA), thus inhibiting DNA synthesis and suppressing cell division and epidermal turnover. 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: Approx 8 hr.
Pharmacokinetics:
Absorption: Well but variably absorbed from the GI tract. Time to peak plasma concentration: Approx 1-4 hr.
Distribution: Taken up by epidermal cells; diffuses into eye lens. Plasma protein binding: 75-91% (mainly to albumin).
Metabolism: Almost completely metabolised.
Excretion: Via urine (approx 95% as metabolites, <0.1% as unchanged drug). Elimination half-life: Approx 0.75-2.4 hr.
Chemical Structure

Chemical Structure Image
Methoxsalen

Source: National Center for Biotechnology Information. PubChem Database. Methoxsalen, CID=4114, https://pubchem.ncbi.nlm.nih.gov/compound/Methoxsalen (accessed on Jan. 22, 2020)

Storage
Store between 15-30°C. Protect from light.
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.
References
8-MOP Capsule, Gelatin Coated (Valeant Pharmaceuticals North America LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 15/01/2016.

Anon. Methoxsalen (Systemic). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 15/01/2016.

Anon. Methoxsalen (Topical). Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 15/01/2016.

Anon. Methoxsalen. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 15/01/2016.

Buckingham R (ed). Methoxsalen. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 15/01/2016.

Methoxsalen Capsule, Liquid-Filled (Actavis Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 15/01/2016.

Oxsoralen Lotion (Valeant Pharmaceuticals North America LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 15/01/2016.

Disclaimer: This information is independently developed by MIMS based on Methoxsalen from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 MIMS. All rights reserved. Powered by MIMS.com
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