Arimidex is available in the UK and generally used for certain forms of precocious puberty.  It depends which studies you have read as to whether it is described as the best aromatase inhibitor or not (it is not the most popular in the UK).     If your son is  already on this and doing well though, I doubt very much that an endocrinologist in London would change his medication.  I understand your reluctance to change his doctor but as Kathy rightly states, it would be advisable to have a doctor over here too, just in case there was an emergency and of course in order to get prescriptions filled.  Please feel free to contact me, should you need any help or advice    Sue@cah.org.uk