Benefits of Inhaled Drug Delivery
Rapid onset, smaller doses → fewer side effects |
Bypasses first-pass metabolism |
Effective for poorly absorbed oral drugs |
Factors Influencing Deposition
Factors Influencing Deposition |
Breath-holding |
Particle aerodynamic diameter |
Humidity & formulation properties |
Spacer Devices
Reduce throat deposition (down to 15% |
Improve lung delivery (~20%) |
Eliminate need for timing coordination |
Require cleaning; bulky |
Formulation Notes
Drug particle: |
~5 µm |
Carrier particle: |
30–60 µm |
Must balance adhesion (mixing) with desorption (release) |
Nebulizers
General Info: |
Converts liquid into inhalable mist |
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Used for large doses, severe attacks |
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Suitable for children and elderly |
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Inhaled during normal breathing |
Types of Nebulisers: |
Jet: |
Uses compressed air; most common |
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Ultrasonic: |
Vibrates crystal → liquid mist |
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Mesh: |
Liquid pushed through vibrating mesh → fine spray |
Mesh Nebulizers offer finer droplets & faster delivery |
Formulation for Nebulizers
- Water-based; may include cosolvents, antioxidants
- pH ~7+ preferred to avoid bronchoconstriction
- Usually 1–2.5 mL dose
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Respiratory System Overview
Air pathway: |
Nasal cavity → pharynx → trachea → bronchi → bronchioles → alveoli |
Bronchi: |
Cartilage rings, cilia for clearing particles |
Bronchioles: |
<1 mm diameter; end in alveoli for gas exchange |
Correct MDI Technique
1.Shake well, prime if needed
2.Exhale fully, seal lips around mouthpiece
3.Inhale slowly & press inhaler
4.Hold breath for 10 seconds
5.Rinse mouth afterward
Breath-Activated Inhalers
Release dose during inhalation (e.g. Easi-Breathe, Autohaler) |
Ideal for patients with coordination difficulties |
Types of DPI Devices
Single Dose (e.g., Cyclohaler): |
Capsule pierced manually |
Multidose – Foil-based (Diskhaler, Accuhaler): |
Blister packs |
Reservoir-based (Turbohaler, Easyhaler): |
Multiple doses, drug stored inside |
New Technology
Thermal Inhalers: |
Thin film drug heated (~400°C), vaporized, and condensed into 1–3 µm particles |
Triggered by breath; compact and efficient |
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Barriers to Drug Delivery
Mucociliary clearance: |
removes particles |
Pathologies: |
inflammation, obstruction, reduced elasticity |
Deposition affected by particle size and breathing pattern |
Aerosol-Based Delivery
Inhalations: |
Vapors from volatile substances or hot water |
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Examples: eucalyptus oil, propylhexedrine |
Vitrellae: |
Crushed glass capsules releasing vapors |
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Example: amyl nitrite for angina |
Dry Powder Inhalers (DPIs)
Overview: |
Breath-activated → no propellants needed |
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Drug in dry powder form, usually with a carrier (e.g., lactose) |
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Requires deep, strong inhalation to disperse powder |
Advantages: |
Larger doses possible |
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No need for coordination |
Disadvantages: |
Performance depends on user’s inspiratory effort |
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Drug exposed to humidity |
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Generally more expensive |
Proper DPI Technique
1.Exhale away from inhaler
2.Inhale quickly and deeply
3.Hold breath 10 seconds
4.Don’t breathe into device (moisture clumps powder)
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Particle Deposition Mechanisms
Inertial Impaction (>5 µm): |
Upper airways |
Sedimentation (~1–5 µm): |
Bronchi/bronchioles |
Diffusion (<0.5–1 µm): |
Alveoli or exhaled |
Ideal size for lung deposition: 1–5 µm
Metered Dose Inhalers (MDIs)
Features: |
Pressurized canister delivers metered dose |
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Propellants: HFA (replaced CFCs) |
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Dose reliability decreases near empty |
Formulation: |
Mostly suspensions due to poor solubility in propellants |
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Evaporation affects particle size |
Advantages |
Only 10–15% of dose reaches lungs |
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High velocity = throat deposition (up to 80%) |
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Requires coordination; poor compliance |
Disadvantages |
Only 10–15% of dose reaches lungs |
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High velocity = throat deposition (up to 80%) |
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Requires coordination; poor compliance |
Key Info
Particle size is key for targeting specific areas in the lungs.
MDIs are common but inefficient unless paired with a spacer.
DPIs require strong inhalation—less suitable for some patients.
Nebulisers are best for high dose delivery in critical care or paediatric use.
New tech like thermal inhalers offers promising advancement.
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