DRUGS USED TO
TREAT DISORDERS OF PIGMENTATION
Hydroquinone interferes with
the production of the pigment melanin by epidermal melanocytes through at least
two mechanisms: it competitively inhibits tyrosi-nase, one of the principal
enzymes responsible for con-verting tyrosine to melanin, and it selectively
damages melanocytes and melanosomes (the organelles within which melanin is
Hydroquinone is applied
topically to treat disorders characterized by excessive melanin in the
epidermis, such as melasma. In the United States, nonprescription
skin-lightening products contain hydroquinone at con-centrations of 2% or less;
higher concentrations are available by prescription.
The incidence of adverse
effects with hydroquinone increases in proportion to its concentration. A
relatively common side effect is local irritation, which may actu-ally
exacerbate the discoloration of the skin being treated. Allergic contact
dermatitis occurs less com-monly. A rare but more serious complication is
exoge-nous ochronosis, in which a yellow-brown pigment de-posited in the dermis
results in blue-black pigmentation of the skin that may be permanent.
Monobenzone (Benoquin) potently inhibits melanin
production and destroys melanocytes. Like hydro-quinone, monobenzone was
originally introduced for the topical treatment of disorders of excess melanin
pig-mentation, including melasma. It is now used only to permanently depigment
the remaining normally pig-mented skin in patients with extensive vitiligo.
Irritant and allergic contact dermatitis are common side effects.