A newly diagnosed diabetic is taught self-injection. He asks his nurse whether he can draw insulin glargine and regular insulin into the same syringe to reduce the number of injections per day. The nurse correctly tells him this cannot be done because:

• A Glargine is formulated at an acidic pH and precipitates on contact with neutral-pH insulins ✓
• B Mixing accelerates degradation of the regular insulin molecule
• C The combination produces immediate systemic hypoglycaemia
• D Regular insulin binds irreversibly to glargine, destroying its activity

Explanation

Insulin glargine is prepared in an acidic solution (pH about 4) so that it remains soluble in the vial but forms microprecipitates when injected into neutral-pH subcutaneous tissue, giving its slow peakless release. Mixing glargine with any other insulin in the same syringe neutralises the solution, causes precipitation inside the syringe and destroys the predictable kinetic profile, so glargine must always be injected separately.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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Written and medically reviewed by the StethoPrep medical team.