If you are to count your first dose (the now dose) as day one, then you take nothing on day 2, and then on day 3 you take your 2nd and final dose, then your prescription (2 tablets) has lasted you for 3 days. Therefore, the days supply is correct and your pharmacy has calculated this correctly.
Patient is prescribed 10g of Glucose. The glucose is presented as a 5% solution in 500ml Saline. How much of the 5% dextrose saline solution do you need