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How does this medication work? What will it do for me?

Methoxsalen belongs to the family of medications known as psoralens. It is used to treat the skin conditions vitiligo, psoriasis, and atopic dermatitis.

For vitiligo, a skin condition where the skin loses its colour in irregular patches, it works by restoring colour to the affected areas. For psoriasis and atopic dermatitis, it is used in combination with high-intensity ultraviolet A (UVA) light therapy. Treatment can last many months.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are being given this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

How should I use this medication?

Capsules: For vitiligo, the usual dose for adults and children over 12 years of age is 20 mg daily, taken 3 to 4 hours (for the regular capsules) or 1 to 2 hours (for the soft gelatin capsules) before exposure to sunlight or UV light treatment. For psoriasis or atopic dermatitis, the dose is based on body weight and taken 1.5 to 2 hours before UV light therapy. Methoxsalen should be taken after meals or with milk.

Lotion: For vitiligo, apply once weekly to a few depigmented areas (areas that are missing skin colour) and expose to UV light for a maximum of one minute. Alternate the sites where you apply the medication. If you are using both the capsules and the lotion, protect the areas where the lotion has been applied from daily exposure to UV light.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are using the medication without consulting your doctor.

It is important to use this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not use a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

What form(s) does this medication come in?

Methoxsalen is no longer being manufactured for sale in Canada and is no longer available under any brand names. This article is being kept available for reference purposes only. If you are using this medication, speak with your doctor or pharmacist for information about your treatment options.

Who should NOT take this medication?

Do not use methoxsalen if you:

  • are allergic to methoxsalen or to any of the ingredients of the medication
  • are 12 years of age or younger
  • are pregnant or may be pregnant
  • are taking medications that increase sensitivity to sunlight
  • have aphasia
  • have a medical condition that increases sensitivity to sunlight (such as porphyria, lupus, or infectious leukoderma)
  • have poor liver function
What side effects are possible with this medication?

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

  • depression
  • dizziness
  • itching of skin
  • nausea
  • nervousness
  • skin changes such as freckles, rash, acne

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

  • blistering and peeling of skin
  • reddened, sore skin
  • swelling (especially of feet or lower legs)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Eye protection: During UV light therapy, wears goggles, and keep your eyes closed. Wear sunglasses while outdoors on treatment days.

Food reactions: Avoid eating limes, figs, parsley, parsnips, mustard, carrots, and celery, as these foods may increase the risk of a more severe reaction to sunlight.

Liver function: People who are using this medication for vitiligo should have their liver function tested monthly for the first few months, and occasionally thereafter.

Medical conditions: This medication should be used with caution by people who have blood clotting conditions or are taking blood thinners (e.g., warfarin).

Overdosage: Overdosage may cause serious burning or blistering. Do not increase the dose or exposure to UV light unless directed by your doctor. If you accidentally take too much medication, call your doctor immediately.

Pregnancy: The safety of this medication for use while pregnant has not been established. It should not be used during pregnancy unless, in the judgment of the doctor, the benefits outweigh the risks.

Breast-feeding: The safety of this medication for use while breast-feeding has not been established. It should not be used while breast-feeding unless, in the judgment of the doctor, the benefits outweigh the risks.

What other drugs could interact with this medication?

There may be an interaction between methoxsalen and any of the following:

  • anticoagulants (e.g., warfarin, heparin)
  • medications that make the skin more sensitive to sunlight (e.g., hydrochlorothiazide, ciprofloxacin, coal tar)
  • other medications that are applied to the skin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

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