5-Amino-1MQ — 12 month update

Dr.BariatricHTX said:

Receptor pharmacology relevant to the pharmacology: semaglutide is a GLP-1R agonist with a C-18 fatty acid chain that enables albumin binding (>99%),…

Semaglutide structural biology relevant to the pharmacology: semaglutide is a 31-amino acid peptide with 94% homology to native GLP-1(7-36). Three key modifications enable its pharmacokinetic profile:

1. Aib8 substitution: DPP-4 resistance (prevents enzymatic degradation)
2. Arg34 substitution: improved chemical stability
3. C18 fatty diacid at Lys26: albumin binding → long half-life

These three modifications transform a peptide with a 2-minute half-life (native GLP-1) into one with a 168-hour half-life (semaglutide). A masterclass in peptide engineering.

Dr.ObesityLA said:

Reading about receptor desensitisation and trying to work out which of the effects adapt over time and which do not, because people clearly experience…

Pharmacist here. I want to add the drug interaction perspective on the pharmacology.

Key points from a pharmacokinetic standpoint:

• GLP-1 agonists delay gastric emptying, which can affect Tmax of co-administered oral medications
• Monitor patients on warfarin (INR), levothyroxine (TSH), and oral contraceptives during dose titration
• The albumin-binding mechanism of semaglutide (C-18 fatty acid linker) gives it the ~168-hour half-life that enables weekly dosing
• Steady state is reached at approximately 4-5 weeks after dose initiation or adjustment

Re: the pharmacology specifically — the pharmacology here is well-characterized and the clinical implications are straightforward.

LarryQC_SD said:

Semaglutide structural biology relevant to the pharmacology: semaglutide is a 31-amino acid peptide with 94% homology to native GLP-1(7-36).

PK/PD modeling for the pharmacology: understanding the pharmacokinetics helps optimize dosing. Semaglutide:

• Tmax: 24-72 hours post-injection
• T½: ~168 hours (7 days) — enables weekly dosing
• Steady state: reached at 4-5 weeks
• Bioavailability (SubQ): ~89%
• Volume of distribution: ~12.5L (primarily plasma)

The albumin binding (>99%) is the key pharmacological innovation — creating a sustained-release effect from a single injection. Previous GLP-1 agonists (exenatide) required BID dosing due to rapid clearance.

One thing that is still open after oliver_london’s answer:

What would you measure differently if you were starting again?

Closing the loop on my own question.

Closing this out: the trough rather than the peak explains the pattern I was seeing on day six, which I had been blaming on the vial.