Adult: In conjunction with controlled exposure to long wavelength UV radiation (solar or artificial): 20 mg or up to 0.6 mg/kg given 2-4 hours before measured periods of UVA exposure. Treatment is given twice weekly or on alternate days, with at least 48 hours interval.
Oral Psoriasis
Adult: For the symptomatic treatment of severe, recalcitrant, disabling cases that are not adequately responsive to other forms of therapy and is diagnosed by biopsy: In conjunction with a schedule of controlled doses of long-wave UV radiation: Patients weighing <30 kg: 10 mg; 30-50 kg: 20 mg; 51-65 kg: 30 mg; 66-80 kg: 40 mg; 81-90 kg: 50 mg; 91-115 kg: 60 mg; >115 kg: 70 mg. Doses are given 1.5-2 hours before measured periods of UVA exposure. Treatment is given 2-3 times weekly, with at least 48 hours interval. Dose may be increased by 10 mg after 15th treatment. Upon achieving 95% clearing or Grade 4 response (complete flattening of plaques including borders), shift to a maintenance therapy of once weekly, then once every 2 weeks, then once every 3 weeks, then as needed to maintain response. Dosage recommendations may vary between countries and available products (refer to specific local guidelines). Elderly: Initiate at the lower end of the dosing range recommended based on body weight.
Parenteral Cutaneous T-cell lymphoma
Adult: For the palliative treatment of skin manifestations of cases (e.g. Sezary syndrome, mycosis fungoides) that are unresponsive to other forms of treatment in conjunction with extracorporeal photopheresis (ECP): Dosage is calculated based on the treatment volume formula: treatment volume x 0.017 = mL of methoxsalen needed. Inject the calculated methoxsalen dose into the recirculation bag before the photoactivation phase; circulate to a Max of 90 minutes while being exposed to UVA light. Do not directly inject into the patient. Following photoactivation, the photoactivated cells are reinfused into the patient within 15-20 minutes; full photopheresis session lasts up to 3 hours. Doses must be administered for 2 consecutive days every 4 weeks for a minimum of 7 treatment cycles (approximately 6 months). If the condition worsens (e.g. increases from baseline) after assessment during the 4th treatment cycle (approx 3 months), may accelerate therapy to 2 consecutive days every 2 weeks for a Max of 20 cycles. May resume regular treatment schedule if condition improves by 25% after 4 consecutive weeks of accelerated therapy.
Administration
Methoxsalen Should be taken with food.
Incompatibility
Solution for extracorporeal inj: May adsorb onto PVC and plastics.
Contraindications
Diseases associated with photosensitivity (e.g. albinism, SLE, porphyria [cutanea tarda, erythropoietic, and variegate], xeroderma pigmentosum), aphakia, severe cardiac disease, severe anaemia, WBC >25,000/mm3, previous splenectomy and coagulation disorders, invasive squamous cell carcinomas, current or history of melanoma.
Special Precautions
Patient with CV disease, ocular disease, multiple basal cell carcinomas or history of basal cell carcinomas, history of x-ray therapy or grenz ray therapy, history of arsenic treatment. Patients who may be unable to tolerate prolonged standing or exposure to heat stress. Hepatic impairment. Elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Actinic degeneration, serious burns, photosensitivity, cataracts, increased risk of skin cancer. Gastrointestinal disorders: Nausea, vomiting. General disorders and administration site conditions: Transient fever (parenteral). Infections and infestations: Infections. Injury, poisoning and procedural complications: Vascular access complication (parenteral). Nervous system disorders: Dysgeusia, dizziness, headache. Psychiatric disorders: Nervousness, insomnia, depression (oral). Skin and subcutaneous tissue disorders: Pruritus, mild transient erythema, hyperkeratosis. Vascular disorders: Hypotension.
This drug may cause transient cardiovascular instability, if affected, do not drive or operate machinery. Men and women must use effective contraception during treatment. Avoid exposure to sunlight for 24 hours before and 48 hours after methoxsalen intake and UVA exposure. Wear UVA absorbing or blocking, wrap-around sunglasses or goggles for 24 hours after methoxsalen intake and even when indoors or near windows for at least 8 hours after methoxsalen treatment. If sun exposure cannot be avoided, apply sunscreen (SPF ≥15) and wear protective clothing (e.g. hat, gloves). Do not apply sunscreen to psoriatic areas until after UVA treatment.
Monitoring Parameters
Evaluate minimum phototoxic dose (MPD) and time to peak phototoxic response after drug administration before initiating photochemotherapy in patients treated for psoriasis. Monitor CBC with differential, renal function, LFTs, and antinuclear antibodies (baseline and every 6-12 months). Perform ophthalmic exam pretreatment and annually. Assess for signs and symptoms of skin cancer, burns, and photosensitivity.
Overdosage
Symptoms: Nausea, vomiting, dizziness. Serious burning and blistering of the skin after exposure to UV light.
Management: Symptomatic and supportive treatment. Perform emesis to empty the stomach. Place the patient in a dark room for at least 24 hours or until skin reaction subsides; initiate supportive treatment for burns as needed. Monitor CV function.
Drug Interactions
May cause additive photosensitising effects with other systemic or topical photosensitising agents (e.g. anthralin, coal tar or coal tar derivatives, griseofulvin, phenothiazines, nalidixic acid, halogenated salicylanilides, sulfonamides, tetracyclines, thiazides, certain organic staining dyes such as methylene blue, toluidine blue, rose bengal, and methyl orange). May increase serum concentrations of caffeine and caffeine-containing products. May enhance photosensitivity with tolbutamide.
Food Interaction
Increased extent of absorption and peak serum concentration with food. Increased risk of phototoxicity with furocoumarin-containing foods (e.g. parsley, celery, lemon, carrots).
Action
Description: Overview: Methoxsalen, a photosensitising agent, is a psoralen derivative and a constituent of the seeds of Ammi majus and the roots of Heracleum candicans. Mechanism of Action: Methoxsalen undergoes activation and binds to pyrimidine bases in DNA, when exposed to long-wavelength UV light, forming mono- and bifunctional adducts that cross-link DNA strands. This photoactivation inhibits DNA synthesis and cell replication. In addition, it can react with proteins and acts as a photosensitiser, enhancing cell damage and inflammation upon UVA exposure. Synonym(s): 8-methoxypsoralen. Pharmacodynamics: In psoriasis or T-cell lymphoma, the therapeutic effect is mainly attributed to DNA photodamage leading to reduced cell proliferation, although vascular, leucocyte, or cell regulatory mechanisms may also contribute.
Following photoactivation, the resulting reaction typically manifests as delayed erythema, appearing several hours after exposure and peaking within 48-72 hours. Exposure to UVA in the presence of methoxsalen can lead to cell injury and inflammation. Over several weeks, the inflammation is followed by repair, characterised by increased epidermal melanisation and thickening of the stratum corneum.
In vitiligo treatment, it has been suggested that melanocytes within hair follicles are stimulated to move upward and repopulate the epidermis.
In the treatment of cutaneous T-cell, the formation of photoadducts results in the proliferative arrest of lymphocytes and they die over a period of about 72 hours. Pharmacokinetics: Absorption: Well but variably absorbed from the gastrointestinal tract. Food or milk may increase absorption. Time to peak plasma concentration: 0.5-4 hours (soft gelatin cap). Distribution: Taken up by epidermal cells; diffuses into the lens of the eyes. Metabolism: Almost completely metabolised in the liver. Excretion: Via urine: Approx 95% (as metabolites). Elimination half-life: Approx 2 hours.
Chemical Structure
Methoxsalen Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 4114, 8-Methoxypsoralen. https://pubchem.ncbi.nlm.nih.gov/compound/8-Methoxypsoralen. Accessed Nov. 27, 2025.
Storage
Oral: Cap: Store at 25°C.
Parenteral: Solution for extracorporeal inj: Store between 15-30°C.
D05BA02 - methoxsalen ; Belongs to the class of systemic psoralens used in the treatment of psoriasis.
References
Brayfield A, Cadart C (eds). Methoxsalen. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 08/10/2025.Methoxsalen (Systemic). UpToDate Lexidrug, Lexi-Drugs Multinational Online. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 08/10/2025.Methoxsalen Capsule, Liquid Filled (Strides Pharma Science Limited). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 08/10/2025.Methoxsalen. Gold Standard Drug Database in ClinicalKey [online]. Elsevier Inc. https://www.clinicalkey.com. Accessed 08/10/2025.Methoxsalen. UpToDate Lexidrug, AHFS DI (Adult and Pediatric) Online. American Society of Health-System Pharmacists, Inc. Waltham, MA. UpToDate, Inc. https://online.lexi.com. Accessed 08/10/2025.Uvadex 20 micrograms/mL Solution for Blood Fraction Modification (Therakos [UK] Limited). MHRA. https://products.mhra.gov.uk. Accessed 08/10/2025.Uvadex Injection, Solution (Therakos LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 08/10/2025.
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