dosage

The administration of a medication etc, in a measured amount; dosing.

The addition of a small measured amount of a substance to something, e.g. sugar to wine.

The measured amount so administered or added (the dose), combined with the frequency of administration and the time period for which it is taken.

Why did he give you only a single 500 mg dose? The correct dosage of this antibiotic is one 500 mg tablet twice a day for 10 days.