depending on his size/weight he can be increased to 5 mg at age six. it is really up to his doctor to determine if he needs a higher dose. he is not "immune" to singulair but his allergies clearly are not in control so his doctor will need to re-evaluated his treatment strategies.
i there a higher dose of singulair for my son? . he is 5yrs old and taking 4mg of singulair but it doesnt seem to be working anymore and he has been taking it continuously for a year is he immune to the medicine now?