Insulin degludec has an ultra-long duration of action (>42 hours) compared to insulin glargine (20–24 hours). The structural basis of degludec's prolonged action is:
- A Substitution of threonine-B30 with a fatty-diacid chain attached via glutamic acid linker allowing albumin binding and multi-hexamer depot formation ✓
- B A single amino acid change at A21 asparagine increasing isoelectric point and causing precipitation at neutral subcutaneous pH
- C Replacement of B28 proline with lysine and addition of two arginine residues at B31-B32 shifting pI to 6.7
- D PEGylation of the B-chain reducing renal clearance and extending half-life in the systemic circulation
Explanation
Degludec has threonine deleted from B30 and a C18 fatty-diacid (hexadecandioic acid) attached to B29 lysine via a gamma-glutamic acid spacer. In the subcutaneous depot, degludec forms stable multi-hexamer chains (di-hexamers linking end-to-end) that dissociate very slowly, releasing monomers for absorption with a half-life of ~25 hours and duration exceeding 42 hours. This provides a flat, peakless action profile with less nocturnal hypoglycemia. Insulin glargine's mechanism involves A21 asparagine substitution and addition of two arginines at B31-B32, which are the features of option C (glargine's structure).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.