antidote to antibiotics

Hi,
my 2 year old has had yet another chest infection. It's the third one in the last 8 months. It has a tendency to start with a croup and within a day develops into a chesty cough (wheezing, rattling, fast breathing no fever). The last time he had croup (in early May) after responding well to aconite and spongia, our homeopath treated him with sulphur 30 and tuberculinum 1M. Cough cleared up withing one week.
2 months later, one day we have a lot of sneezing, by the end of the next he's starting to try to cough and in the night it starts again: fast breathing, wheezing with lots of mucus and a tickly cough.
Nasal discharge was clear and very profuse. Homeopath prescribed aconite first in 30, later in 200, together with Ipecac 30 (as my son had a couple of coughing attacks with belching and gagging). There was no change, by the late evening his breathing got worse, cough became very painful and although homeopath suggested to try sulphur again, we ended up giving antibiotics as the situation was worrying.
We have finished the antibiotics course today. I haven't really heard him coughing today anymore.
I would love to antidote the penicilin. I read arsenicum alb can neutralize its damage. Do you agree? What are your suggestions, also regarding his tendency to have reoccurring chest infections? Another problem is that he has a craving for sweets... Would be grateful for your help.