Photosensitivity methoxsalen

Another method that may have less carcinogenic potential is to topically deliver the photosensitizer (methoxsalen) to the skin by adding it to bath water (bath PUVA) or as a topical cream (PUVA cream) instead of through systemic administration. Advantages of this approach include minimal risk of systemic effects, overall reduction of PUVA dose to one-... 

There is a bath PUVA and an oral PUVA. Bath PUVA therapies involve soaking in a bath of psoralens liquid for 15 minutes prior to UVA treatment. Oral PUVA involves taking an oral psoralens capsule the day prior to a UVA treatment. Oral psoralens such as methoxsalen cause nausea in many patients. Other adverse effects of PUVA include photosensitivity, which necessitates the use of eye protection and UVA-blocking sunscreen for 24 hours after a PUVA treatment macular melanosis at exposed sites (PUVA lentigines) and increased risk of skin cancers, especially squamous cell carcinoma.21... 

Contraindications Cataract, invasive squamous cell cancer, aphakia, melanoma, diseases associated with photosensitivity, hypersensitivity to methoxsalen (psoralens)... 

Recognition of the photosensitizing effect of the naturally occurring furanocoumarin psoralin (desmethoxy (3-6)) led to trials of its utility for the treatment of skin diseases such as psoriasis. The partial effectiveness of this compound led to the preparation of synthetic analogues. The two commercially available drugs, methoxsalen (3-8) and trioxsalen (4-6), are used in a procedure that goes by the acronym PUVA (psoralen and UVA irradiation) for the treatment of psoriasis and other skin diseases. 

Systemic PUVA is approved for the treatment of psoriasis. It consists of oral ingestion of a potent photosensitizer such as methoxsalen (8-methoxypsoralen) at aconstant dose (0.6 to 0.8 mg/kg) and variable doses of UVA, depending on patient skin type and history of previous response to ultraviolet radiation (see Table 96-6 for skin type classifications ). Approximately 2 hours after ingesting psoralen, the patient is exposed to UVA light. Photochemotherapy is performed two or three times a week. In most patients, control and partial clearing occurs by the twenty-fifth treatment. 

Photosensitizing and phototoxic chemicals found in more than two dozen plant sources, including celery, parsnips and parsley. Major compounds psoralen, methoxsalen, tri-oxsalen, bergapten and imperatorin. Stimulate melanocyte response to UV. 

Methoxsalen is a psoralen that acts as a photosensitizer. A psoralen derivative with pigmenting properties (12 to 20 mg p.o.), methoxsalen is used to induce repigmentation in vitiligo. 

The psoralens are absorbed rapidly after oral administration. Photosensitivity typically is maximal 1 to 2 hours after ingestion of methoxsalen. There is significant but saturable first-pass elimination in the liver, which may account for variations in plasma levels among individuals after a standard dose. Methoxsalen has a serum half-life of approximately 1 hour, but the skin remains sensitive to light for 8 to 12 hours. Despite widespread drug distribution throughout the body, it is photoactivated only in the skin where the UVA penetrates. 

Ultraviolet A (UVA) may also be used to suppress mitotic (cell division) activity. Photochemotherapy, a combination of ultraviolet radiation with a psoralen derivative, methoxsalen (photosensitive dmg), is used to decrease prohferation of epidermal cells. This is called psoralen and ultraviolet A (PUVA) and permits lower doses of dmg and ultraviolet A to be used. 

A 35-year-old woman taking methoxsalen and undergoing PUVA for psoriasis unexpectedly developed increased photosensitivity. Over the previous weekend and on the morning of therapy she had been drinking a concoction of rue (Ruta graveolens) This plant naturally contains 5-methoxypsoralen so it would appear that a pharmacodynamic interaction occurred, which resulted in the photosensitivity. 

Methoxsalen and trioxsalen are derived from a family of benzofuran-containing plant natural products known as psoralens. Both methoxsalen and trioxsalen act as photosensitizers that decompose in the presence of UV light into active metabolites that crosslink DNA. These compounds have found significant use in the treatment psoriasis, eczema, and vitiligo. 

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