I don't know anything about detoxosode...a google search didn't net much, only that it's a homeopathic medication? Maybe? I will be up front here & admit that I'm not a great believer in using homeopathics for very serious conditions. Others may disagree with me on this & fair enough. In any case, whether or not detoxosode is homeopathic, your post had some red flags in it for me. Most worryingly, heavy metal poisoning in a 4 month old infant? I mean, holy crap, that's really serious stuff. Personally, I'd be ripping apart (metaphorically, of course) everything in our environment to figure out how a child, who is presumably only breast or formula fed, has toxic levels of metal in his body. What kind of metal are we talking about? Lead, mercury, what? Also, can I ask what kind of testing was done to give this result? Is it possible that there's some error in the testing process? The thing that gets me is where does a child, who's only been four months on this earth, get heavy metal poisoning? Are you scarfing down 10 cans of tuna a day, and then nursing him? Are you living next to some facility that could be leaching metals in the water, which then gets fed to your son? Is he eating lead-based paint flakes? And what kind of symptoms is he exhibiting that caused the suspicion of metal poisoning in the first place? Because, depending on what type of metal we're talking about, that's pretty severe stuff.
I honestly don't believe that eliminating that long list of foods could be the cause of metal poisoning. That just doesn't make sense. And the fillings? Well, maybe, but there'd be a LOT of children out there with metal poisoning if that were the case. I think what I'm saying here is that this may be a case that's too serious to be dealt with with alternative modalities (and I'm a fan of alternative modalities, just not for everything). Best of luck, and I hope your LO gets better soon!
ETA: not meaning to imply you haven't investigated your environment. I was just floored that such a young child could have metal poisoning.