Mixtard and Insulin Glargine Cannot Be Mixed Together
No, Mixtard insulin and insulin glargine (Lantus) should never be mixed in the same syringe. Insulin glargine must not be mixed with any other insulin formulation due to the low pH of its diluent, which would alter the pharmacokinetic properties of both insulins and lead to unpredictable glucose control 1, 2.
Why This Mixing Is Contraindicated
Chemical Incompatibility
- Insulin glargine has an acidic pH (pH 4) in its diluent that is essential for maintaining its solubility and extended duration of action 1.
- When mixed with other insulins (including Mixtard, which contains NPH and regular insulin), the pH changes cause insulin glargine to precipitate prematurely, destroying its long-acting properties 3, 4.
- The FDA label explicitly states: "Do not dilute or mix Insulin Glargine with any other insulin or solution" 2.
Loss of Pharmacokinetic Profile
- Insulin glargine is designed to precipitate slowly after subcutaneous injection in the neutral pH environment of tissue, providing its characteristic flat, peakless 24-hour action 3, 4, 5.
- Mixing with other insulins before injection disrupts this mechanism, resulting in unpredictable absorption and loss of the basal insulin coverage that glargine is designed to provide 3, 4.
What You Should Do Instead
Administer as Separate Injections
- Give Mixtard and insulin glargine as two separate injections at different injection sites 2.
- Rotate injection sites within the same anatomical region (abdomen, thigh, or deltoid) to reduce risk of lipodystrophy 2.
- Use separate syringes for each insulin type to avoid any cross-contamination 2.
Timing Considerations
- Insulin glargine should be administered once daily at the same time each day (can be morning or evening, but must be consistent) 2, 4, 5.
- Mixtard is typically given 30 minutes before meals, with timing based on the specific formulation (e.g., Mixtard 30/70 contains 30% regular and 70% NPH) 6.
Critical Pitfalls to Avoid
Never Use the Same Syringe
- Even if you draw the insulins separately and don't physically mix them, residual insulin glargine in the syringe dead space can contaminate other insulins 2, 7.
- The American Diabetes Association explicitly warns that no other medication or diluent should be mixed with any insulin product unless approved by the prescribing physician 1.
Don't Confuse with NPH Mixing Guidelines
- While rapid-acting and short-acting insulins CAN be mixed with NPH insulin (the protamine-based component in Mixtard), this does NOT apply to insulin glargine 1, 6.
- Insulin glargine is fundamentally different from NPH due to its acidic pH formulation, making it incompatible with all other insulin types 1, 2.