Jan 24, 2024 at 12:54 AM#1
I've been on compounded semaglutide for 6 months (great results, 32 lbs down) and my provider wants to switch me to compounded tirzepatide for potentially better results. Before I switch, I want to understand: are there quality/stability differences between compounded tirz and compounded sema that I should know about?
I know they're different molecules, but are there compounding-specific concerns that differ between the two?
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Jan 24, 2024 at 1:02 AM#2
Excellent question, and yes, there are meaningful differences from a compounding perspective:
Molecular Complexity:
- Semaglutide: 31 amino acids, molecular weight ~4,114 Da
- Tirzepatide: 39 amino acids, molecular weight ~4,810 Da
Tirzepatide is a larger, more complex peptide with a dual-action mechanism (GIP + GLP-1 receptor agonist). This additional complexity has implications:
Stability:
- Tirzepatide is generally considered LESS stable in solution than semaglutide
- More susceptible to aggregation at higher concentrations
- More sensitive to pH deviations — optimal stability is in a narrower pH range
- The fatty acid side chain (C20) in tirzepatide is different from semaglutide's (C18), affecting formulation compatibility
- Some compounders report more lot-to-lot variability with tirz formulations
Formulation Challenges:
- Tirzepatide can be more difficult to get into solution at higher concentrations
- Requires more careful buffer selection
- More prone to adsorption onto container surfaces (which can reduce effective concentration)
- Some preservative systems that work well with sema may interact differently with tirz
Beyond-Use Dating:
- Given the stability differences, BUDs for compounded tirz tend to be shorter than sema
- A compounder who assigns a 90-day BUD for their semaglutide should NOT automatically apply the same BUD to their tirzepatide without separate stability data
Last edited: Jan 24, 2024 at 3:02 AM
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Sigma-Aldrich — Research-Grade Standards
Certified reference materials, analytical reagents, and research-grade standards for peptide verification. Trusted by laboratories worldwide.
Shop Reference StandardsJan 24, 2024 at 1:18 AM#4
Yes, I'd argue that quality vetting is even more important for compounded tirzepatide than semaglutide. Here's what to specifically ask about for tirz:
1. "Do you have separate stability data for your tirzepatide formulation?" — Don't accept "we use the same BUD as our semaglutide." Different molecule = different stability profile.
2. "What concentration do you compound tirzepatide at?" — Common concentrations are 5mg/mL, 10mg/mL, and sometimes higher. Higher concentrations can be more prone to aggregation. Make sure they have stability data at the specific concentration you'll be receiving.
3. "How do you address the adsorption issue?" — Tirzepatide can stick to glass and rubber surfaces, reducing the effective dose. Branded Mounjaro uses a surfactant (polysorbate 20) to prevent this. Ask if your compounder addresses this in their formulation.
4. "What buffer system do you use?" — Branded Mounjaro uses a phosphate buffer at pH 5.8. If your compounder is using a significantly different buffer or pH, ask about stability data in THEIR specific system.
5. Potency testing is critical. Given the adsorption and stability concerns, a Certificate of Analysis showing potency testing for tirzepatide is even more important than for sema.
8 11Dr.ObesityMed, HealthEcon_DC, PedsEndoPhilly and 5 others
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Jan 24, 2024 at 1:59 AM#5
I switched from compounded sema to compounded tirz 3 months ago. My experience with quality:
The good:
- My pharmacy (503B, PCAB-accredited) was very transparent about the formulation differences
- They compound tirz at 10mg/mL in a phosphate buffer with polysorbate 20
- BUD is 60 days (shorter than their sema at 90 days)
- CoA shows 98.5% potency at time of release
The concerning:
- The tirz solution is slightly more viscous than the sema was, making it harder to draw into the syringe
- I noticed the tirz seems more sensitive to temperature — one time I left it on my counter for 2 hours and the next dose seemed less effective (could be placebo, could be degradation)
- The cost is higher — $340/month vs $280/month for sema — which my pharmacy attributed to higher API costs and more complex formulation/testing requirements
The results:
- After 3 months on tirz, I've lost an additional 14 lbs beyond what I'd achieved with sema (which had plateaued)
- Appetite suppression is stronger
- GI side effects were worse initially but have leveled off
Overall, very happy with the switch, but I keep the tirz refrigerated religiously and never leave it out.
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