A patient with type 2 diabetes is started on NPH insulin 10 units at bedtime. He is instructed to roll the vial between his palms before injection. NPH insulin requires resuspension because it is formulated as:
- A A protamine-zinc-insulin crystalline suspension with isophane (equal) protamine-to-insulin ratio ✓
- B A clear acidic solution of insulin hexamers stabilized by zinc ions
- C A neutral solution of insulin monomers with surface-active stabilizers
- D An albumin-bound insulin complex in phosphate buffer
Correct answer: A. A protamine-zinc-insulin crystalline suspension with isophane (equal) protamine-to-insulin ratio
Explanation
NPH (Neutral Protamine Hagedorn) insulin is a suspension of insulin complexed with protamine at an isophane ratio, forming crystals that dissolve slowly at the injection site, giving intermediate duration (10-16 hours). It must be resuspended by rolling before injection. Clear solutions like insulin glargine or regular insulin do not require resuspension.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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