Azelaic acid (AZA) is a naturally occurring 9-carbon dicarboxylic acid compound isolated from cultures of Pityrosporum Ovale. It inhibits tyrosinase activity in vitro (Kj = 2.73 X 10 3M) and may also interfere with DNA synthesis and mitochondria activity in hyperactive and abnormal melanocytes. AZA has been used to treat melasma and postinflammatory hyperpigmentation and to arrest the progression of the lentigo maligna to melanoma. This specificity may be attributed to its selective effects on abnormal melanocytes (16). AZA produced ultra structural damage to normal melanocytes (17).
AZA cream has been reported to be of benefit in the treatment of melasma. The cream is applied twice daily and most patients report a mild but transient irritation and dryness of the skin at the beginning of the treatment. In the treatment of melasma, a 24-week study in South America found that a 20% concentration of AZA was equivalent to 2% HQ (18). In the Philippines, a study found that 20% AZA was better than 2% HQ. Three hundred and twenty nine patients with melasma were treated with 20% AZA and 4% HQ. Fifty six percent of the AZA group had good or excellent results while 73% HQ had a similar result (19).
Topical potent steroids and 20% AZA cream combines the beneficial effects of both besides perhaps increasing the compliance of the patients (20). AZA with tretinoin caused more skin lightening after three months than AZA alone, and a higher proportion of excellent responders at the end of treatment (16). The combination of AZA 20% cream and glycolic acid 15% or 20% lotion was as effective as HQ 4% cream in the treatment of hyperpigmentation in darker skinned patients, with only a slightly higher rate of mild local irritation (21).
Particular advantages of AZA therapy include its favorable safety and side effect profile. It is non-teratogenic, is not associated with systemic adverse events or photodynamic reactions, exhibits excellent local tolerability, and does not induce resistance in Propionibacterium acnes (22). Adverse effects from the AZA included irritant contact dermatitis that was usually mild and transient, but occasionally was pronounced.