It is strange because I can
find plenty of reference to to products containing calcium carbonate 700 mg and magnesium hydroxide 300 mg but I can not
find any products for sale online with that combination (I checked PetCo, PetSmart, CVS, Walmart, Amazon); plenty with 1200 mg, 600 mg etc... I would ask your Veterinarian about
local stockists for this since he is making the recommendation, plus I don't know which country you are in.