Isotretinoin--an explanation for its long-term benefit.

Isotretinoin is of undisputed benefit in the treatment of acne. In doses of 1 mg/kg/day for 4 months the drug produces a highly significant reduction in sebum excretion rate (90 +/- 3%) in comedone formation as measured by assessing follicular casts (70 +/- 5%), and in surface Propionibacterium acnes. However, the mechanisms of long-term clinical remission are not well understood. There are however, risk factors which predetermine the outcome to treatment with isotretinoin. Younger subjects (14-19 years) and those who have had acne for less than 6 years, respond less well than older subjects. Subjects with more truncal acne also fare less well than those with predominantly facial acne. A return of the reduced sebum excretion rate to within 10% of the pre-treatment level also is a poor prognostic factor. This and future studies could lead to development of more logical dose regimes depending, for example, on the age of the patient; duration of acne and its site. However, until proven otherwise, this study confirms our earlier data, and that of the German multi-centres and Strauss et al (1), that the optimum dose schedule for treating acne patients is 1 mg/kg/day regime.