I went looking for why the dosing schedule is what it is and found that almost every practical question on this board has a pharmacokinetic answer nobody states.
The question I want answered is which effects tachyphylax and which persist, because the answer explains why tolerability improves while the appetite effect keeps working.
I have searched first, so if this is covered somewhere point me at it and I will read it.
DadBodDave said:I went looking for why the dosing schedule is what it is and found that almost every practical question on this board has a pharmacokinetic answer…
Receptor pharmacology relevant to the pharmacology: semaglutide is a GLP-1R agonist with a C-18 fatty acid chain that enables albumin binding (>99%), creating a depot effect with a ~168-hour half-life enabling weekly dosing[1].
Tirzepatide is a dual GIP/GLP-1R agonist with higher GIP affinity (5:1 GIP:GLP-1 potency ratio). The GIP component may enhance beta-cell function and adipocyte lipid metabolism beyond what GLP-1 alone achieves.
For the pharmacology, the pharmacology explains the clinical differences between these agents.
[1] Lau J, et al. J Med Chem. 2015;58(18):7370-7380.
DebRD_ATL 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%),…
DebRD_ATL has the substance of this right. The condition it depends on is worth stating. The pharmacokinetics explain nearly every practical question asked here. Albumin binding above 99% slows clearance enough to make weekly dosing possible; a terminal half-life near a week means four to five weeks to steady state and therefore a four-week titration interval; subcutaneous bioavailability around 89% means injection site barely matters. Those three facts answer most timing questions before they are asked.
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Browse GL BiochemDadBodDave said:I went looking for why the dosing schedule is what it is and found that almost every practical question on this board has a pharmacokinetic answer…
This matches mine closely enough to be worth saying so out loud. The detail I would add is minor and it is already implied above.
From the other side of the consultation, briefly.
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.