Methyl aminolevulinate photodynamic therapy

Author: Vanessa Ngan, Staff Writer, 2003.

What is methyl aminolevulinate?

Methyl aminolevulinate (MAL) is a topical photosensitising agent that is used in photodynamic therapy (PDT). It is available as a 16% strength cream in a 2g tube. The trade name is Metvix™.

Metvix movie

How does methyl aminolevulinate PDT work?

When applied to the skin, methyl aminolevulinate is selectively absorbed into cancer cells. The drug is converted into photoactive porphyrins, naturally-occurring intracellular photosensitising chemicals that bind with iron to make haemoglobin. When cancer cells full of porphyrins are exposed to specific wavelength of light (570-670 nm), a molecular reaction occurs that results in destruction of the cancer cells.

What is methyl aminolevulinate PDT used for?

Methyl aminolevulinate is classed as an antineoplastic agent (anti-cancer drug) and is approved for use in New Zealand for the treatment of:

MAL-PDT is recommended for lesions that are unsuitable for other available therapies due to possible complications and/or poor cosmetic outcome. It may be particularly useful for lesions on the mid-face or ears, lesions on severely sun damaged skin, large lesions or recurrent lesions.

Clinical trials around the world using MAL-PDT have shown it to have comparable cure rates to other conventional treatments such as cryotherapy or surgery. A distinct advantage of MAL-PDT is that it selectively targets tumour cells. This means that surrounding healthy cells are not affected by the treatment thus leaving minimal scarring and a much better cosmetic outcome.

How is MAL-PDT given?

MAl-PDT involves a two-stage process. The first stage is application of the methyl aminolevulinate cream.

The second stage involves exposing the lesion to light.

After treatment the lesions will be covered with an occlusive dressing for at least 24 hours. Lesions usually heal completely within one to four weeks. More than one lesion can be treated in a single treatment session. A repeat second treatment may be done approximately one week later: this is recommended for most basal cell carcinomas and thicker actinic keratoses.

Your practitioner will arrange to check the lesions after about 3 months. If they show a non-complete response re-treatment may be necessary.

Precautions during MAL-PDT

If MAL-PDT treatment is very painful, exposure to the light can be temporarily stopped. When ready to recommence, the light source can be moved further away (e.g. twice the distance) from the treatment area, and exposure recommenced. The exposure time will need to be adjusted (e.g. twice as long for the remaining exposure). Slower treatments are usually less painful.

Side effects of MAL-PDT

Approximate 60-80% of patients undergoing MAL-PDT experience some side effects. These are usually related to the treated area being sensitive to light and are like sunburn. Side effects are of mild to moderate intensity and usually subside within a few days after treatment.

As the skin cancers cells die off, the lesion may blister and ulcerate. This generally heals within 4 weeks.

Frequency of reported side effects
Very common
  • Burning sensation
  • Stinging sensation
  • Pain
  • Swelling
  • Crusting
  • Redness
Common
  • Itchiness
  • Ulceration
  • Suppuration
  • Blisters
  • Peeling
  • Skin infection
  • Hyper/hypopigmentation
Uncommon
  • Urticaria

Storage and handling of methylaminolevulinate cream

Metvix movie

The Metvix™ QuickTime movie is approx 2 1/2 minutes in duration (4.3MB). Click here to view the movie.

MAL-PDT using natural daylight

Daylight-mediated PDT is a convenient form of treatment of thin actinic keratoses on the face and scalp. Results have been shown to be as good as with conventional MAL-PDT (described above). Treatment can be undertaken during spring, summer or autumn in most parts of the world.

The natural daylight PDT procedure is as follows:

Natural daylight PDT is followed by sunburn-like inflammation in treated areas for 5 to 8 days. The skin is red, and may become blistered and crusted. The reaction tends to be most severe at 3 to 4 days after treatment. Redness can be reduced by pre-treatment with topical steroid

Similar cure rates and excellent cosmetic results are described for actinic keratoses. Advantages of natural daylight PDT include:

Daylight MAL-PDT may also be undertaken indoors. Lux should be > 5,000 for it to be effective in the treatment of actinic keratoses. Options include:

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