It's only a partial answer, but a Nile crocodile can eat up to half its body weight at a sitting, according to National Geographic. Since few freshwater fish weigh half as much as a crocodile, we can probably assume these croc feasts occur when they're able to ambush ungulates (e.g. zebras and antelope).
Probably best to stick to the recommended dosing on the bottle though. For adults, that's 400-800mg four times a day (Maximum 3200mg/day US labelling or 2400mg/day Canadian labelling) Dosing for children is weight based. If your symptoms persist for more than 24 hours with ibuprofen, you should probably see your physician rather than keep taking the drug. Unless you are allergic to it, or have gastric issues such as ulcers or gastritis. Or have kidney disease, or advanced liver disease, or heart disease, or late in pregnancy.
That is a safe dose, but you may not be taking enough. The maximum dose of ibuprofen is really 3200 mg and you are taking 400 mg. Since I don't know your medical history or your weight, so you can address you dosage with your doctor. Medically, you may be able to increase your dose to 600 mg each time; up to 3 or 4 times per day if your arthritis warrants it.