Why must insulin glargine never be drawn into the same syringe with NPH or any other insulin?
- A Mixing destroys the arginine residues essential for receptor binding
- B NPH proteolytically degrades glargine within minutes
- C The acidic solution of glargine precipitates when mixed with the neutral phosphate buffer of other insulins, blunting its prolonged action ✓
- D Mixed insulins develop antibodies that neutralize both preparations
Correct answer: C. The acidic solution of glargine precipitates when mixed with the neutral phosphate buffer of other insulins, blunting its prolonged action
Explanation
Glargine is formulated at acidic pH (about 4) to keep it soluble in the vial. On injection into neutral subcutaneous tissue it precipitates, creating the depot responsible for its flat 24-hour profile. Mixing with neutral-buffered insulin such as NPH neutralizes the solution, causing precipitation inside the syringe and unpredictable, shortened absorption. Receptor binding is unaffected by mixing, there is no proteolysis by NPH, and antibody formation is not the issue.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.