Accurate insulin dosing is key when it comes to managing diabetes. When even a half of a unit of insulin is too much, diluting insulin can be exceptionally useful for people on injection therapy.

For adults and children who use insulin to manage diabetes, getting the dose just right is critical. Generally, insulin injections (via a syringe or a pen) are administered in either 1 unit or ½ unit increments. In contrast, for those who use an insulin pump, much more precise dosing is possible. However, diluting insulin is an option that can allow individuals on injection therapy to achieve accurate insulin dosing and avoid hypoglycemia without having to eat additional carbohydrates.

Why Dilute Insulin?

Most insulins come in the U-100 formulation. This means that there are 100 units of insulin per 1 mL of solution. Some insulins are also available in more concentrated (e.g., U-200, U-500) or less concentrated (e.g., U-50) forms.

For many who are on insulin injection therapy, dosing the commonly available preparation of U-100 insulin in ½ or 1 unit increments is sufficient to obtain the desired blood glucose control. However, some people are incredibly insulin sensitive, and a ½ unit injection can often be too much. In this case, diluting insulin to achieve a lower concentration for more appropriate dosing is a reasonable consideration.

Who Dilutes Insulin?

Different situations may necessitate insulin dilution. For example, an individual who is very active or newly-diagnosed may be extremely insulin sensitive. Similarly, infants and young children often require very low doses of insulin. Those with a slower-progressing form of type 1 diabetes (i.e., LADA) may want to use very small amounts of insulin to keep in the normal range and take the pressure off their pancreas. Finally, individuals who eat a low-carbohydrate diet (especially in combination with another variable above) may have very low insulin dosing requirements.

How to Dilute Insulin

The diluent is a sterile and appropriately-buffered solution. The specific composition of the diluent may vary depending on the manufacturer. Diluent solutions are available for many fast-acting insulins, including the commonly-used Humalog and Novolog. The manufacturers of the commonly-used basal insulin analogs, Levemir and Lantus, state that these insulins should not be diluted, as doing so will alter their activity profiles.

Notably, Eli Lilly, the manufacturer of Humalog, states that “Humalog in a vial may be diluted with STERILE DILUENT for Humalog®, Humulin® N, Humulin® R, Humulin® 70/30, and Humulin® R U-500 to a concentration of 1:10 (equivalent to U-10) or 1:2 (equivalent to U-50). Diluted Humalog may remain in patient use for 28 days when stored at 5°C (41°F) and for 14 days when stored at 30°C (86°F). Do not dilute Humalog contained in a cartridge or Humalog used in an external insulin pump.”

Here is a basic calculation example of how to dilute insulin:

If U-100 insulin is diluted ten-fold, a concentration of U-10 (meaning, 10 units per 1 mL of solution, instead of 100 units per 1 mL) would result. Here is a simple equation to use: C1 x V1 = C2 x V2 Where, C1 = initial concentration; V1 = volume of initial concentration to add; C2 = desired (diluted) concentration; and V2 = final volume of the (diluted) solution. For instance, if one wishes to prepare 1 mL of U-10 insulin, the equation would be set up as follows: (100 U/mL) x (V1) = (10 U/mL) x (1 mL); in solving for V1, we obtain 0.1 mL (of concentrated insulin to add). So, one would add 0.1 mL of the U-100 insulin to a new sterile vial or syringe, and then add 0.9 mL of the diluent, to obtain 1 mL of U-10 insulin, now ten times less potent than the original.

Sterile glass vials are available for purchase online, while syringes (e.g., ½ mL or 1 mL) are available in most states without a prescription at a pharmacy, or can be ordered online.

Where to Obtain Diluent

Diluent can be ordered directly from the insulin manufacturer. It does not require a prescription, but it typically cannot be shipped to a home setting; rather, it must be requested to be shipped to your doctor’s office or pharmacy.

It is a good idea to contact the manufacturer of your insulin first and ask them how to go about requesting the diluent. Sometimes, there is a specific form that can be completed and submitted with your request.

Obstacles to Diluting Insulin

In general, diluting insulin is not common practice, and sometimes physicians advise against it. This can be for a number of reasons, such as a lack of understanding of the benefits, or concerns over whether the patient will perform the dilution correctly. Some practitioners may even advise a higher carbohydrate intake to match more typical insulin usage, which undoubtedly can be disconcerting to patients.

Some patients may understand the value of diluting insulin but become discouraged from the idea by an unsupportive healthcare provider. Others may not feel confident in their calculations or dilution techniques, so may be unsure of their ability to correctly dilute and use the insulin preparation.

Finally, some confusion about ordering can become an obstacle. Anecdotally, patients have reported struggling to obtain the diluent. This largely stems from general unawareness of the practice and lack of clear ordering guidelines. Some providers and pharmacists may even be confused about whether diluent can be obtained in the outpatient setting. It can be helpful to get in touch with the manufacturer ahead of time to obtain any relevant request forms and protocols.

Conclusions

Although it is not common practice, diluting insulin can be an important tool to achieve more precise insulin dosing for patients who require very small amounts of insulin. If you believe that diluting insulin is the right way forward for yourself or your child, talk to your healthcare provider. If you are not on the same page, it may be worthwhile to get a second opinion.

Since diluent is available without a prescription and can be ordered directly from the manufacturer to be shipped to any pharmacy or doctor’s office, anyone who wants to dilute insulin can do so. However, it is incredibly important to perform the dilution correctly (make the appropriate calculation, avoid contamination, etc.) so it is always a good idea to discuss the practice with a healthcare provider, especially for those who are not entirely confident in the procedure.

Have you ever diluted or considered diluting insulin? We would love to hear about your experience!

Read more about children with diabetes, Humalog, insulin, insulin pumps, Lantus, Levemir, Lilly Diabetes (Eli Lilly), low blood sugar (hypoglycemia), low-carb diet, NovoLog, type 1 diabetes.