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According to my doctor, 4 hours. You can switch them up. Take acetaminophen, (Tylenol), then wait 4 hours and take Ibuprofen, wait another 4 hours and take acetaminophen and so on. :) 15 people found this useful.
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.