Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
Metvix (Galderma)
2 g tubes of cream containing 160 mg/g
Approved indications: actinic keratoses, basal cell carcinoma
Australian Medicines Handbook section 14.3
Squamous cell carcinomas can develop from actinic keratoses. While some keratoses will resolve with reduced exposure to sunlight others need to be removed. As an alternative to surgical treatments, severe cases can be treated with topical fluorouracil. Methyl-5-aminolevulinate, which is a porphyrin precursor, is another antineoplastic drug that can be applied directly to the lesions.
After applying methyl-5-aminolevulinate, the lesion is covered with an occlusive dressing for three hours. This results in the accumulation of the porphyrins which are produced by the enzymatic conversion of methyl-5-aminolevulinate. The lesion is then exposed to a dose of red light. This light activates the intracellular porphyrins causing damage to the cells. The treatment is repeated one week after the first application. If there is no response after three months the patient can be re-treated once.
In an Australian study there was a complete response in 71 of 88 patients with solar keratoses. A placebo cream resulted in only 3 of 23 patients responding. The complete response rate of 81% was greater than the 60% who responded to one treatment of cryotherapy. A European study also compared the two treatments, but found that the response rate to cryotherapy was higher (75%) than the response to methyl-5-aminolevulinate (69%).1
Methyl-5-aminolevulinate can also be used to treat basal cell carcinoma. Although a few more patients will respond to photodynamic therapy than cryotherapy (95% v 91%), the response rate is less than that of surgical excision (90% v 98%). Recurrences are also less likely after surgical excision, but photodynamic therapy may give a better cosmetic outcome. Methyl-5-aminolevulinate can therefore be considered for superficial or nodular basal cell carcinomas where surgery is inappropriate.
As methyl-5-aminolevulinate is a photosensitiser it can cause phototoxic reactions. Patients should not expose the treated areas and surrounding skin to sunlight for two days after treatment. Burning, pain, redness and oedema are very common adverse effects. Some patients develop blisters or skin ulcers. In the European study more of the patients had a reaction to methyl-5-aminolevulinate than to cryotherapy (43% v 26%).1
Methyl-5-aminolevulinate works best on keratoses which are not hyperkeratotic. If treatment is successful it gives a good cosmetic result. It can therefore be considered for thin lesions on the face or scalp when other treatments are unsuitable.
