Peptide Fillers

The most common “filler” or excipient used in lyophilized peptides is mannitol. It’s widely used as a bulking agent and stabilizer during freeze-drying.

Other common fillers/stabilizers include:

• Trehalose — protects peptide structure during freeze-drying

• Sucrose — similar role to trehalose

• Glycine — used as a bulking agent and pH stabilizer

• Buffer salts — phosphate or histidine buffers

• Occasionally polysorbate 20/80 in some formulations

Why they use them:

• Helps create the visible white “cake” in the vial

• Protects the peptide during lyophilization

• Improves stability and shelf life

• Makes reconstitution easier

• Reduces degradation and aggregation

In the research peptide world, mannitol is by far the most common. Some suppliers advertise “no filler” peptides, but many properly lyophilized peptides still contain small amounts of stabilizers.

That’s why at Apex Labs we don’t use fillers.