the (preferred) chemical composition of Norvasc is:
Active ingredient: amlodipine besylate, corresponding to either 5 or 10mg of amlodipine base
sodium starch glycollate - a disintegrant
microcrystalline cellulose - a compression aid
magnesium stearate - a lubricant
dibasic calcium phosphate - an additive that provides sheen
Besylate salt is the same as benzene sulphonate salt. During the manufacturing process, they prepare this salt by reacting the amlodipine base with a solution of benzenesulphonic acid in an inert solvent (a methylated spirit).
Sulfonic acid...A.K.A. benzemonosulfonic acid... is considered a synthetic intermediary for sulpha drugs.
Sulfur, sulfite and sulfates are not likely to cause problems for people with a sulfa allergy. There are some drugs that are related to sulfonamides- such as a diuretic hctz- that can cause problems in some people. The drugs to watch for if one has a sulfa allergy are sulfa antibiotics, some diabetes medications, sulfasalasine for IBD, some COX 2 inhibitors and some migraine medication. The BEST source of information is your pharmacist - always check with him/her. They know everything (well, their databases do!!!)
P.S. I checked a list of sulpha drugs in one of my books just to be sure - Norvasc is not on it. That does not mean that some people won't react adversely to this medication. Talk to your pharmacist.