Everyone seems to have this under control, but i would throw in my two cents:
The bottle says do not take more than 6 200mg tablets in 24 hours. This is over the counter strength. Prescription strength is 800 mg (4 200mg tablets for you slow people) every 6 hours.
The immediate results are simply reduced pain, but ibuprofin therapy really becomes effective after a 2-3 day window. Pain relief is still evident, but the antinflammatory response is much more pronounced. This is when ibuprofin is much more useful. You can continue this program for 2-3 weeks with little side effect.
However, it is very helpful to drink ALOT of water, which helps reduce the irritation and long-term side effects on both the stomach and the kidneys.
DO NOT drink alcohol when doing this program. Seriously. This amount of ibuprofin is not great for the stomach or kidneys, but putting alcohol into the mix can cause liver failure and big-time kidney problems, let alone stomach bleeding and intestinal irritation. blood in poop, urine, vomiting, trouble digesting, etc. Not pretty.
definitely ask your doctor too. they are pretty open and honest about ibuprofin, since it is so commonly taken for pain. they'll also tell you what drug interactions are bad too.
Broken ribs suck. watch for punctured organs because you can die, and that means you can't paddle, which defeats the whole reason you took advil.