Humulin R U500 is a concentrated insulin that contains 5 times as many units of insulin per ml as U100. It is also dispensed in a 20 ml vial versus 10 ml for the U100. This often causes confusion for many clinicians, pharmacists, educators and pharmacy benefit plans when trying to adjust doses or calculate day’s supply.
One 20ml vial of u500 insulin has the same effective amount of insulin as 10 vials of U100 insulin as both of the quantities offer the same amount of insulin coverage. This means that it takes one fifth as much volume of U500 to deliver the same amount of insulin coverage as it does for U100.
Another way to look at this would to look at how we dispense medications. As an example, if a prescription is written for lisinopril 20 mg we can either give the patient 1 tablet of 20 mg or 4 tablets of 5 mg. The total amount of lisinopril is the same but there is a difference in the strength of the tablets that dictate the quantity.
In the same way if we need to give the patient 100 units of insulin we could choose to load the syringe with 100 units of U100 or 20 units of U500.
Calculating the day’s supply for quantity purposes for insurance works in the same way.
In the case of the lisinopril we could either give the patient 120 5mg tablets or 30 20mg tablets for a 30 day supply.
Likewise if we have a patient using 100 units of U100 three times a day, a 30 day supply would be 9000 units of coverage or 90ml a month and our patient would need 9 vials to fill that order. If they were using U500 they would still need 9000 units of coverage but since the U500 is 5 times as strong they would only need 18ml per month or one vial to fill the order.