It is such a horrible feeling when you first get sick from taking something you have been able to take before. I developed an allergy in adult hood.. Was half way through a box, and had a reaction, couldn't breath and got rushed to hospital...

But anyhow, there are things to take instead. Erythramycin is what I normally take now if I need something, but there are others.. As I have a bad reaction(even to touch of it), I wear a medi-alert bracelet, and all around me know that I can't take it.. Even DD who is 3 knows some medicine makes mummy very sick..