My son is 19lbs how muc tylenol (acetaminophen) can he have 160mgs for teething?

Yes, most likely.: There is a range of tylenol (acetaminophen) dosing that is considered both safe and effective. To give your son 160mg on an occasional (two to four times daily) basis would be acceptable. However, it would not be wise to give every 4 hours, day and night, around the clock because of the potential to build up in his body to potentially worrisome blood levels. Talk with your pediatrician about this.

Consider this: I would rather see you use cold rings for your child than to rely on medications. All kids go through this and having them chew on these will get the teeth to break through the gums quicker solving your problem.