 [ Symptoms ] 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 [ Disease ] depending on his sizeweight 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