18mo has a fever past two days. Gave tylenol (acetaminophen) at 7:15p. Can I give ibprofen @9:45p. Hasn't had ibprofen since 3:45p. Don't want him to go to bed w/o?

Using both. For healthy children you can alternate between Acetaminophen and Ibuprofen for fever. Typically Acetaminophen (tylenol) is used every 4-6 hours and Ibuprofen (motrin/advil) is every 6-8 hours. You should ask your physician or pharmacist for specific dosage amounts. If the fever continues i would seek further care.