dosage / dose
The regimen versus the single amount.
A dose is one measured amount. Dosage is the schedule or the size of the doses as a plan. Give a dose. Follow the dosage. Mixing the two is common. Keep dose for the single amount.
Examples
Usea 5-milligram dose
Usethe daily dosage
Avoida 5-milligram dosage (If you mean one amount.)