Xanthotoxin

Uses

Repigmentation of vitiliginous areas, Psoriasis, Repigmentation of vitiliginous areas

Xanthotoxin is also used to associated treatment for these conditions: Cutaneous T-Cell Lymphoma (CTCL), Vitiligo, Idiopathic Vitiligo, Refractory peripheral cutaneous T-cell lymphoma, Severe Psoriasis

How Xanthotoxin works

After activation it binds preferentially to the guanine and cytosine moieties of DNA, leading to cross-linking of DNA, thus inhibiting DNA synthesis and function.

Dosage

Xanthotoxin dosage

Topical-

Adult use:

• 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. Protect the area surrounding the lesion with 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.
• Psoriasis: 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.

Geriatric use: Refer to adult dosing.

Pediatric use

(Children ≥12 years): Vitiligo: Refer to adult dosing.

Oral (Adult)-

Repigmentation of vitiliginous areas: 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, with at least 48-hr intervals.

Psoriasis: 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, 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.

Hands and fingers of person applying the lotion should be protected to prevent possible photosensitization and/or burns.

Side Effects

Major Side Effects are-

• Blistering and peeling of skin
• reddened, sore skin
• swelling, especially of the feet or lower legs

There is an increased risk of developing skin cancer after use of methoxsalen. You should check the treated areas of your body regularly and show your doctor any skin sores that do not heal, new skin growths, and skin growths that have changed in the way they look or feel.

Premature aging of the skin may occur as a result of prolonged methoxsalen therapy. This effect is permanent and is similar to the result of sunbathing for long periods of time.

Precaution

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.

Interaction

May increase plasma concentration of drugs metabolised by CYP2A6 isoenzyme. Additive effect with other systemic or topical photosensitising agents (e.g. anthralin, coal tar, nalidixic acid).

Food Interaction

• Take with food. Take this medication with food or milk.

[Moderate] GENERALLY AVOID: The ingestion of foods containing photosensitizing components (e.g., limes, figs, parsley, parsnips, rue (Ruta graveolens), mustard, carrots and celery) may increase the risk of photosensitivity and severe burning during methoxsalen therapy.

Two cases of photosensitivity involving

rue and a soup containing celery, parsley, and parsnip have been reported in PUVA patients.

MANAGEMENT: Patients who are undergoing PUVA treatment and taking methoxsalen should be advised to avoid eating large quantities of these foods.

Xanthotoxin Drug Interaction

Moderate: celecoxib, sulfamethoxazole / trimethoprimUnknown: charcoal, mupirocin topical, varenicline, ubiquinone, copper gluconate, rosuvastatin, glucose, diltiazem, multivitamin, arginine, metoprolol, metoprolol, acetaminophen, bioflavonoids, sildenafil, thiamine, cholecalciferol, rivaroxaban

Xanthotoxin Disease Interaction

Major: aphakia, photosensitivity states, skin cancerModerate: cardiac disease, liver disease, previous x-ray therapy, sunburn

Half Life

Approximately 2 hours

Elimination Route

In both mice and man, methoxsalen is rapidly metabolized. Approximately 95% of the drug is excreted as a series of metabolites in the urine within 24 hours (Pathak et al. 1977).

Pregnancy & Breastfeeding use

Xanthotoxin lotion has been assigned to pregnancy category C by the FDA. Animal reproduction studies have not been conducted with topical methoxsalen, although it has been shown to be a potent photocarcinogen in certain strains of mice. There are no controlled data in human pregnancy. It is also not known to what extent, if any, methoxsalen is absorbed systemically following topical administration. Xanthotoxin lotion is only recommended for use during pregnancy when benefit outweighs risk.

Contraindication

Aphakia, existing or history of melanoma, invasive squamous cell carcinoma, photosensitivity diseases (e.g. porphyria, acute lupus erythematosus, xeroderma pigmentosum).

Storage Condition

Store between 15-30° C. Protect from light.

Innovators Monograph

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