Why Peptide Delivery Routes Cannot Be Ranked in General

“Spray or injection?” is not a complete scientific question. The answer depends on the molecule, formulation, intended site of action and clinical purpose. A route that works well for one medicine may be poorly suited to another.

FDA's nasal-product guidance addresses formulation, container and manufacturing controls for products intended to act locally or systemically. Its existence reflects an important principle: the delivery system is part of the product that must be evaluated. FDA nasal spray chemistry manufacturing and controls guidance

Separate exposure from outcome

A formulation can change how much material reaches a tissue and how variable that exposure is. Demonstrating exposure, however, is different from demonstrating a meaningful clinical benefit. A product may reach the circulation without improving the outcome being claimed.

Conversely, a locally acting product may need evidence at its intended site rather than a simplistic comparison of blood levels. A qualified pharmacologist should define the relevant measurements and explain why they answer the study's question.

Each route has its own quality questions

Sterile injectable medicines require manufacturing controls relevant to their route. Nasal products have different formulation and device-performance questions. Neither route confers quality merely by being convenient, invasive or familiar. The relevant finished product must be evaluated. FDA sterile drug aseptic processing guidance

For research communication, a useful comparison identifies the same molecule and a clearly specified formulation in each arm. It then states whether the evidence comes from cells, animals or humans, and whether it concerns exposure, tolerability or efficacy. If those elements differ, the comparison should say so rather than announce a universal winner.

This AXON article does not recommend a route, explain how to convert products or provide administration instructions. Product-specific evidence and appropriate clinical review are necessary before drawing conclusions about human use.