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Since they are drugs that are in different classes most pediatricians are comfortable with them being dosed simultaneously. So long as ibuprofen is dosed 6hrs from ibuprofen and tylenol is dosed 4h fro tylenol, the two don't matter much to each other. If the ibuprofen isn't working and he hasn't had tylenol in at least 4hrs you could dose it now. Usually ibuprofen works a little better at getting fever down. If you would like to tell me how much he weighs I'd be happy to review your dosing with you.