I believe jittery / rapid heart beat are well know side effects in some people. You can probably find more information about those on the web. Maybe double check (with the information published by the drug company ) your dose. I believe it is by weight. We were first prescribed a dose that was too high - but was most likely convenient for a reasonable amount of time -- for convenience...

I stopped it when we began GSH inhalations. Recently we resumed due to illness - but I plan to wean off again asap if possible.