Can you take 1 ibuprofen 600mg 4-5 hours after taking 2 extra strength tylenols (acetaminophen) that are not working well?

Yes. But don't do this on a regular basis. Normally, it's recommended that you take 4 tabs of Ibuprofen 600 mg a day and 4-6 tablets of tylenol (acetaminophen) 500 mg a day. So if you combine both, i'd suggest 2 each of the tylenol (acetaminophen) and Ibuprofen per day on alternating doses. Don't drink alcohol with it. Drink lots of liquids. If you develop stomach upset, nausea, vomiting or fever, go see yourdr take care!