You apparently have one of these doctors who doesn’t like to think too hard about pharmaceuticals.
Allopurinol is in many countries sold in 100mg and 300mg pills because that allows the following simple combinations by manufacturing or stocking only two different pills:
-50mg is half a 100mg pill
-150mg is half a 300mg pill
-200mg is two 200 pills
-400mg is a 300mg pill and a 100mg pill
And so forth. You get the idea.
You can take whatever dose you like. But I would not recommend tripling your dose without intermediate steps!
There are a whole lot of side effects people have gotten from allopurinol, most of which you’ll thankfully never experience. Probably you’ll experience zero effects but for sure you’re never going to have to deal with most of them. So I don’t think there’s much point in researching horror stories.
Instead, I recommend you simply follow generally accepted guidelines such as:
-start low (which is what you’ve done so far) and increase the dose slowly and progressively (this is the part your doctor doesn’t care to bother with)
-take as much allopurinol as needed to reach the desired uric acid level and no more
If you increase your dose slowly, you should notice most side effects before they become a serious problem. Then you could go back to a lower dose or switch to a different drug. Unfortunately, some nasty side effects are hard to notice at first and sometimes there is no going back to a lower dose once you get other side effects. But my assumption is that in your situation the risk would be minimal if you increase your dose slowly.
And if you indeed got down to 0.30 mmol/l after only a few weeks on 100mg, I dare say you clearly have no use for a large dose anyway. But if I may keep harping on the same point: you should get at least one more blood test. Then settling on an appropriate dose would be less of a guessing game.