Intranasal Administration: Bioavailability & Effectiveness

This research article explains how intranasal peptide delivery works, what limits or improves bioavailability, which peptides are better suited for this route, and how to use nasal sprays properly for more consistent results.

How Intranasal Peptide Delivery Works

The inside of the nose is lined with a thin, moist membrane called the nasal mucosa. It contains:

• A rich blood supply
• A thin layer of mucus
• Specialized cells and tight junctions (small seals between cells)

When a nasal spray is used, the peptide solution is sprayed onto this surface. From there, absorption can occur through two main pathways:

• Paracellular route: between cells, through tight junctions when they are slightly open
• Transcellular/endocytic route: through the cells by endocytosis (cells “swallowing” small particles or molecules)

Reviews of intranasal peptides show that molecules up to around 6,000 Daltons (a measure of size) have been delivered across the nasal mucosa, although efficiency is often low.

Because the nasal cavity is small, the volume per spray is limited (often around 50–100 microliters per nostril). Peptides must be quite soluble so that enough drug can be delivered in this small volume.

Bioavailability: Why It Is Often Low

Bioavailability describes the percentage of an administered dose that reaches systemic circulation in active form. For many intranasal peptides, human bioavailability is generally below 5%.

Several barriers reduce intranasal bioavailability:

• Mucociliary clearance: Tiny hairs and mucus in the nose move particles toward the throat to be swallowed and removed. This clearance can remove a large part of the dose before it can be absorbed.
• Enzymatic breakdown: Enzymes present in nasal mucus and cells can break down peptide bonds, reducing the amount of intact peptide that crosses the membrane.
• Tight junctions and cell membranes: The nasal lining is designed to protect the body. Tight junctions limit passage between cells, and cell membranes are lipid‑rich, which makes it hard for large, water‑loving peptides to cross.
• Limited surface area and volume: The total area accessible to sprays and the small dose volume limit how much peptide can be successfully delivered at one time.

Because of these factors, many intranasal peptide products produce relatively low systemic levels compared with injection. However, for some use cases, even low systemic exposure may be acceptable if the peptide is potent.

Nose‑to‑Brain Pathways

Intranasal delivery is especially interesting for peptides that act on the brain. The nose provides potential “shortcut” routes that may bypass part of the blood–brain barrier (BBB), which blocks many drugs from entering the brain.

Peptides can move along:

• Olfactory pathways: following nerves involved in smell
• Trigeminal pathways: following sensory nerves that innervate the nasal cavity

These routes may allow small amounts of peptide to reach brain tissues more directly than through standard blood circulation.

Research on nose‑to‑brain delivery shows that:

• Intranasal peptides can reach central nervous system targets in animal and human studies.
• This route avoids first‑pass metabolism in the liver.
• It may support treatment of conditions such as pain, neurodegenerative diseases, and psychiatric disorders.

However, the exact mechanisms and efficiency vary widely by peptide, formulation, and spray technique.

Factors That Affect Intranasal Bioavailability

Several controllable and uncontrollable factors influence how much peptide is absorbed.

Peptide Properties

• Molecular weight and size: Smaller peptides absorb better; most successful intranasal peptides are below about 6 kDa.
• Charge and polarity: Neutral or slightly lipophilic (fat‑loving) molecules cross cell membranes more easily than highly charged, hydrophilic ones.
• Stability: Peptides that resist enzymatic breakdown in mucus and on cell surfaces retain more activity during absorption.

Formulation and Excipients

Modern intranasal peptide formulations often use:

• Permeation enhancers: ingredients that temporarily loosen tight junctions or alter membrane fluidity to increase absorption (for example, surfactants or specific lipids).
• Mucoadhesive polymers: such as chitosan, which help the spray stick to the nasal lining longer, slowing clearance and increasing contact time.
• Buffers: to optimize pH for stability and comfort.
• Preservatives: to maintain sterility, although these must be chosen carefully to avoid irritation.

Studies show that adding permeation enhancers and mucoadhesives can significantly increase intranasal peptide bioavailability in both animals and humans.

Patient and Technique Factors

• Nasal congestion: Swelling or mucus from allergies, colds, or structural issues can reduce contact between spray and mucosa.
• Spray angle and head position: Aiming slightly outward and back (not toward the septum) and keeping the head slightly tilted forward often improves coverage of the lateral nasal wall, where absorption is better.
• Timing with blowing the nose: Blowing the nose right after spraying removes the medication. Waiting several minutes supports better absorption.
• Breathing during spraying: Many instructions recommend gentle inhalation during the spray, not deep sniffing, to avoid pulling the solution straight into the throat.

Peptides That Suit Intranasal Administration

Not all peptides are good candidates for intranasal use. The best fits usually share these features:

• Low to moderate molecular weight
• High potency (effective at low doses)
• Some resistance to nasal enzymes
• A clear benefit from either rapid absorption or potential nose‑to‑brain delivery

Reviews of intranasal peptide therapeutics highlight examples such as oxytocin analogs, certain pain‑related peptides, and experimental neuroprotective peptides, though specific products and indications vary by region and regulatory status.

Because of low bioavailability, intranasal dosing often requires:

• Higher nominal doses compared with injection
• Careful formulation to balance absorption, safety, and comfort

Practical Intranasal Administration Technique

Good technique can help maximize consistency and effectiveness.

Step 1: Prepare the Nose

• Gently blow the nose before use to clear thick mucus.
• Avoid using vasoconstrictor nasal sprays at the same time unless directed by a clinician, as these can alter blood flow and absorption.

Step 2: Position the Head and Device

• Sit or stand upright with the head slightly tilted forward.
• Insert the spray tip into one nostril, pointing slightly outward, away from the nasal septum (the midline wall) to reduce irritation and improve lateral wall coverage.

Step 3: Spray and Breathe

• While gently breathing in, press the pump to release the spray.
• Do not take a deep sniff; the goal is to coat the nasal mucosa, not send the liquid straight to the throat.
• Repeat in the other nostril if required.

Step 4: After Spraying

• Avoid blowing the nose for at least 10–15 minutes.
• Try not to lie flat immediately after use, as this may promote drainage to the throat.
• If an unpleasant taste appears in the mouth quickly, technique may be sending too much spray posteriorly.

Safety and Tolerability Considerations

Common local side effects from intranasal sprays include:

• Mild burning or stinging
• Sneezing
• Nasal dryness or mild irritation

These usually relate to preservatives, permeation enhancers, or a non‑optimal pH in the formulation. Severe or persistent irritation warrants evaluation and a review of the formulation and dosing frequency.

Rare but more serious concerns include:

• Significant nosebleeds
• Signs of infection (pain, swelling, or pus)
• Possible structural changes with very long‑term use of certain excipients

Clinical development of intranasal peptide products includes monitoring nasal health with imaging and examinations to ensure long‑term safety.

Comparing Intranasal with Injection Routes

Intranasal delivery offers unique pros and cons compared with subcutaneous or intramuscular injection.

Advantages:

• Needle‑free and generally more acceptable to many people
• Rapid onset, often similar to parenteral routes for some peptides
• Potential nose‑to‑brain access, especially valuable for central nervous system targets

Limitations:

• Often low and variable bioavailability (commonly under 5% in humans for many peptides)
• Sensitive to nasal health and technique
• Limited dose volume and concentration constraints
• More complex formulation needs (enhancers, mucoadhesives, stabilizers)

Because of these trade‑offs, intranasal administration is best suited for peptides where:

• High potency compensates for low bioavailability
• Rapid onset or nose‑to‑brain transport offers a distinct clinical advantage
• Needle avoidance is a strong priority and can improve adherence