What is methoxsalen? How does it work (mechanism of action)?
- Methoxsalen is a naturally occurring photoactive chemical found in the seeds of the Ammi majus (Umbelliferae) plant and in the roots of Heraclem candicans. It belongs to a group of compounds known as psoralens, or furocoumarins. It is used for treating psoriasis, idiopathic vitiligo (leucoderma) and cutaneous (skin) manifestations of T-cell lymphoma. The exact mechanism of action of methoxsalen is not known.
- Methoxsalen has several biological actions that may be responsible for its medical effects. Ultraviolet radiation of 320-400 nm wavelength (UVA) is beneficial for treating psoriasis, vitiligo, and skin manifestations of T-cell lymphoma. Methoxsalen is a photosensitizer that increases the reaction of the skin to UVA. Methoxsalen also combines with DNA in skin cells. Upon administration, methoxsalen reaches the skin via blood. When UVA penetrates the skin, cellular damage occurs, leading to inflammation. The damaged skin heals after several days to weeks.
- Some experts suggest that methoxsalen improves vitiligo by stimulating melanocytes (melanin forming skin cells) to move up the hair follicle and to repopulate the epidermis. Psoriasis causes an over production of skin cells. Methoxsalen may benefit psoriasis by decreasing skin cell production by damaging DNA.
- The FDA approved methoxsalen capsules in December 1954.
- 8-MOP, Oxsoralen Ultra are the brand names for methoxsalen.
- Methoxsalen is available in generic form.
- You need a prescription to obtain methoxsalen.
What are the uses for methoxsalen?
- Oral methoxsalen combined with UVA (ultraviolet A) radiation is used as photochemotherapy for the treatment of severe, disabling psoriasis that is difficult to treat and is unresponsive to other treatments.
- It also is used for treating idiopathic vitiligo (leucoderma) and cutaneous (skin) manifestations of T-cell lymphoma.
What are the side effects of methoxsalen?
Common side effects include:
Other side effects include:
- Edema
- Dizziness
- Headache
- Malaise
- Depression
- Hypopigmentation
- Leg cramps
- Rash
- Low blood pressure
- Stomach upset
Possible serious side effects include:
- Severe burns from over exposure to UVA or sunlight
- Blisters
- Keratosis
- Sun sensitivity
- Worsening of psoriasis
- Basal cell carcinoma
- Premature aging
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What is the dosage for methoxsalen?
- Patients must not sunbathe 24 hours before methoxsalen administration and UV exposure because a sunburn may prevent an accurate evaluation of the response to treatment.
- UVA-absorbing wrap-around sunglasses designed to prevent entry of radiation to the eyes should be worn during the day for 24 hours after methoxsalen administration.
- Patients must avoid sun exposure, including through-the window or through cloud cover, for at least 8 hours after methoxsalen administration. Hat and gloves, and/or sunscreens with SPF equal to or greater than 15 should be used if sun exposure cannot be avoided. Sunscreens should be applied to all areas of the body exposed to the sun (including lips). However, sunscreens should not be applied to areas affected by psoriasis until after treatment in the UVA chamber.
Psoriasis
- The recommended oral dose for treating psoriasis is 10 to 70 mg every other day with milk or food 2 hours before UVA exposure. The dose is based on weight.
Cutaneous T-Cell Lymphoma
- The recommended initial oral dose for treating cutaneous T-Cell lymphoma is 0.6 mg/kg. Ann additional 10 mg should be taken if the blood concentration of methoxsalen is less than 50 ng/ml.
Vitiligo
- The recommended oral dose for treating vitiligo is 20 mg every other day with milk or food 2 to 4 hr before UVA exposure. The dose must not exceed 0.6 mg/kg since larger doses may result in serious skin burns.
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Which drugs or supplements interact with methoxsalen?
- Use of drugs that cause sun sensitivity will increase the risk of severe skin burns when using methoxsalen. Examples of such drugs include coal tar or coal tar derivatives, doxycycline (Vibramycin), tetracycline, demeclocycline, methylene blue (Provayblue), griseofulvin (Gris-PEG), thiazide diuretics, fluoroquinolone antibiotics, and several other drugs.
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Is methoxsalen safe to take if you are pregnant or breastfeeding?
- Methoxsalen has not been adequately studied in pregnant women. Animal data suggest that methoxsalen can harm the fetus when used by a pregnant woman. Women of childbearing potential should be advised to avoid becoming pregnant.
- It is not known whether methoxsalen is excreted in human milk.
What else should you know about methoxsalen-oral?
What preparations of methoxsalen-oral are available?
Capsule: 10 mg
How should I keep methoxsalen-oral stored?
Methoxsalen should be stored at 15 C to 30 C (59 F to 86 F).