A multi-center, single-arm, open-label study was conducted in 28 girls with McCune-Albright Syndrome and progressive precocious puberty aged 2 to < 10 years. All patients received a 1 mg daily dose of ARIMIDEX. The trial duration was 12 months. Patients were enrolled on the basis of a diagnosis of typical (27/28) or atypical (1/27) McCune-Albright Syndrome, precocious puberty, history of vaginal bleeding, and/or advanced bone age. Patients' baseline characteristics included the following: a mean chronological age of ± years, a mean bone age of ± years, a mean growth rate of ± cm/year and a mean Tanner stage for breast of ± . Compared to pre-treatment data there were no on-treatment statistically significant reductions in the frequency of vaginal bleeding days, or in the rate of increase of bone age (defined as a ratio between the change in bone age over the change of chronological age). There were no clinically significant changes in Tanner staging , mean ovarian volume, mean uterine volume and mean predicted adult height. A small but statistically significant reduction of growth rate from ± cm/year to ± cm/year was observed but the absence of a control group precludes attribution of this effect to treatment or to other confounding factors such as variations in endogenous estrogen levels commonly seen in McCune-Albright Syndrome patients.
One Arimidex side effect of importance is the possibility of Estrogen rebound. This exists in particular with two of the three most popular aromatase inhibitors (Arimidex and Letrozole). The third aromatase inhibitor, Aromasin (Exemestane) does not share this same attribute of the possibility of Estrogen rebound. This is because unlike Aromasin, Arimidex is a non-suicidal aromatase inhibitor. This means that Arimidex will bind with and disable the aromatase enzyme, but it does not do it permanently. At some point, Arimidex will dissociate with the enzyme and the enzyme will then be free to do its job again in the body. What this means for the end user is the risk of a rebound of Estrogen levels (and thus, Estrogen related side effects) if Arimidex use is halted too soon or abruptly after beginning use.