What U-500 means
Humulin R U-500 contains 500 units of insulin in each mL.[1] One unit is therefore 0.002 mL, a fifth of the volume of a U-100 unit. ISMP describes confusion between U-500 and U-100 as a cause of five-fold dosing errors.[4]
mL = U-500 units ÷ 500 · U-500 syringe lines = U-500 units ÷ 5
How the U-500 syringe is marked
BD's U-500 syringe, cleared by the FDA in 2016, is a 0.5 mL syringe with bold U-500 scale markings in 5-unit increments, for doses up to 250 units, with a 6 mm × 31G needle, and is available by prescription only.[2] Lilly's instructions add that each line measures 5 units of U-500 insulin, that the syringe has a green U-500 symbol and a green needle shield, and that it can give 5 to 250 units in one injection.[1]
| U-500 units | mL | Lines on the U-500 syringe |
|---|---|---|
| 5 units | 0.01 | 1 |
| 25 units | 0.05 | 5 |
| 50 units | 0.1 | 10 |
| 75 units | 0.15 | 15 |
| 100 units | 0.2 | 20 |
| 150 units | 0.3 | 30 |
| 200 units | 0.4 | 40 |
| 250 units | 0.5 | 50 |
Why a U-100 syringe gives the wrong number
Before the dedicated syringe, U-500 doses were measured in “syringe units” on U-100 or tuberculin syringes. ISMP's example: 200 units of U-500 insulin was drawn to the 40 mark on a U-100 syringe.[4] The arithmetic holds (40 marks = 0.4 mL = 200 units of U-500), but the printed number is a fifth of the real dose, which made orders and labels easy to misread. In 2016 ISMP recommended that U-100 and tuberculin syringes no longer be dispensed for U-500 and that doses be written in actual units of U-500.[3] Lilly's instructions warn that any other syringe, such as a U-100, tuberculin or allergy syringe, can give the wrong dose and may cause a dangerous overdose.[1]
No conversions at homeThis page explains the scale. It is not a guide to measuring U-500 with any other syringe. Follow the instructions of the prescriber who ordered U-500 insulin.
Pens: never draw into a syringe
As of the July 2026 US label, Humulin R U-500 is listed only as a KwikPen, a 3 mL pen holding 1,500 units. The label says not to transfer U-500 from the pen into any syringe and not to perform dose conversion when using the pen.[1] ISMP has described the reverse error too: dialling old “syringe units” on a pen gives one fifth of the prescribed dose.[3]
Other concentrated insulins, at 200 and 300 units per mL, are sold only in pens, and their labels say never to draw them from the pen into a syringe because overdose and severe low blood sugar can result.[5][6][7] Syringe math on this site does not apply to them.
Related guides
Why syringes marked in mL caused trouble with concentrated insulin is explained in insulin vs tuberculin syringes. The volume of any number of U-500 units sits alongside U-100 and U-40 in 1 mL = how many units. The other big scale mix-up, U-40 against U-100, is on U-40 vs U-100 syringes, and the full list of errors is in syringe measuring mistakes.
Frequently asked questions
What is a U500 syringe?
The dedicated U-500 insulin syringe: 0.5 mL, marked in 5-unit lines of U-500 insulin up to 250 units, with a 6 mm × 31G needle.
How many units are in 1 mL of U-500 insulin?
500 units. Each unit is 0.002 mL.
How is a U-500 syringe marked?
The dedicated U-500 syringe holds 0.5 mL and is marked in 5-unit lines of U-500 insulin, up to 250 units.
Can I use a U-100 syringe for U-500 insulin?
The U-500 label warns that a U-100, tuberculin or allergy syringe can give the wrong dose and may cause a dangerous overdose. Use only what your prescriber has ordered.
Sources
- Humulin R U-500 (insulin human) prescribing information and instructions for use
- BD receives FDA clearance for new syringe designed for the administration of Humulin R U-500 insulin
- Medication Safety Alert! Community/Ambulatory Care, vol. 15 no. 9: misuse of new insulin strengths; new U-500 syringe
- ISMP Guidelines for Optimizing Safe Subcutaneous Insulin Use in Adults
- Humalog (insulin lispro) prescribing information
- Tresiba (insulin degludec) prescribing information
- Toujeo (insulin glargine) prescribing information