Excipient compatibility is a critical step in peptide formulation development. Selecting the right excipients ensures stability, bioavailability, and patient safety. This reference covers common excipients, testing protocols, and known incompatibilities.
| Excipient | Purpose | Compatible Peptides | Notes |
|---|
| BAC (0.9%) | Antimicrobial | Most peptides | Standard preservative |
| Mannitol | Bulking agent | All | Lyophilization aid |
| Sucrose | Cryoprotectant | All | Stabilizes during freeze-dry |
| Tween 80 | Surfactant | Aggregation-prone | Reduces surface adsorption |
| EDTA | Chelator | Metal-sensitive | Prevents metal-catalyzed oxidation |
| Glycine | Tonicity agent | Injectable | Adjusts osmolality |
| Buffer | pH Range | Advantages | Disadvantages |
|---|
| Phosphate | 5.8–8.0 | Physiological, well-characterized | Precipitates at low pH |
| Acetate | 3.6–5.6 | Good for acidic peptides | Volatile, may evaporate |
| Citrate | 3.0–6.2 | Broad range, chelating | May chelate metal ions |
| Tris | 7.0–9.0 | Common in research | Temperature-dependent pH |
| Histidine | 5.5–6.5 | Protein-stabilizing | Expensive at scale |
| Material | Compatibility | Notes |
|---|
| Borosilicate glass | Excellent | Industry standard |
| Type I glass | Excellent | Low extractables |
| COP/COC plastics | Good | Low protein binding |
| Silicone elastomers | Variable | May absorb hydrophobic peptides |
| Stainless steel | Good | For manufacturing only |
- Visual inspection — clarity, color, particulates
- pH measurement — stability of formulation pH over time
- Potency assay — bioactivity retention at 25°C and 40°C
- Aggregation — SEC-HPLC for aggregates and fragments
- Degradation — RP-HPLC for degradation products
- Particulate matter — USP <788> sub-visible particles
- Sterility — USP <71> for injectable formulations
- Extractables/leachables — container-closure studies
| Peptide | Incompatible | Reason | Alternative |
|---|
| Insulin | Ethanol | Denaturation | Use aqueous buffers |
| Oxytocin | Strong acids | Hydrolysis | pH > 3.0 |
| BPC-157 | None known | Highly stable | — |
| GHK-Cu | EDTA | Chelates copper | Use citrate instead |
| Semaglutide | Extreme pH | Degradation | pH 6.0–7.5 |
| GLP-1 analogs | Organic solvents | Aggregation | Aqueous only |
