Effect of metformin on glucose disposal and hyperinsulinaemia in a 14-year-old boy with acanthosis nigricans.

We report the treatment of a 14-year-old Indian boy with acanthosis nigricans and hyperinsulinaemia with metformin in an attempt to improve his skin lesions. Oral metformin was used for 6 months with assessment of insulin status during an intravenous glucose tolerance test and hyperinsulinaemic-euglycaemic clamping before and after treatment. The first-phase insulin response reduced from 19,593 to 5,410 pmol/l/min (normal 1,900-13,400), and the second-phase insulin response improved from 59,120 to 34,020 pmol/l/min (normal 2,900-18,100). During hyperinsulinaemic-euglycaemic clamping hepatic glucose production was normally suppressed prior to therapy, but peripheral glucose remained abnormally low, 152 and 138% of basal (expected 199%). The acanthosis nigricans remained unaltered but over this period puberty progressed and his body mass index increased. We conclude that, in this patient, metformin had a minimal effect on the hyperinsulinism and none on the acanthosis nigricans in the relatively short term, but further studies in more patients over longer time intervals are warranted.