Inhalation Product Design and Testing

Key aims of inhaler device design?

Consistent drug delivery, high lung penetration, compact design, minimal side effects.

Challenges in inhaler device design?

Cost, lack of excipients, inefficient delivery, poor targeting, toxicology, patient acceptability.

Why is in vitro testing important for inhalers?

Predicts in vivo performance, simpler, cheaper, detailed analysis, supports 3Rs (reduction, refinement, replacement).

What does BP testing for inhalers involve?

Dose uniformity, fine particle dose, aerodynamic size, number of doses, preservative efficacy, leakage.

What is 'uniformity of delivered dose'?

Ensures consistency of dose emission throughout device life.

Critical parameters for DPI testing?

Flow rate producing 4 kPa pressure drop or maximum 100 L/min, draw 4 L air volume.

What is fine particle fraction (FPF)?

Portion of dose with particles <5μm, critical for lung deposition.

What technique measures aerodynamic particle size?

Cascade impaction.

How do cascade impactors work?

Separate particles by inertia across multiple stages with decreasing nozzle sizes.

Devices for aerodynamic particle size measurement?

Glass impinger, Multi-stage liquid impinger (MSLI), Andersen Cascade Impactor (ACI), Next Generation Impactor (NGI).

Main drawback of glass twin impinger?

Limited particle size distribution information.

Advantages of Andersen Cascade Impactor (ACI)?

Stack-up design, replaceable damaged stages.

Features of Next Generation Impactor (NGI)?

Uses collection cups, operates 15–100 L/min, high precision, tests pMDIs, DPIs, nebulisers.

How is the number of deliveries per inhaler tested?

Discharge inhaler to waste, must meet labeled number of doses.

How is antimicrobial preservative efficacy tested?

Inoculate product with microorganisms, assess survival/fall after defined storage.

Leakage testing for pMDIs?

Weight before and after standing; acceptable if mass loss <10% over shelf life.

Tidal breathing simulations are used for which devices?

Nebulisers.

Critical breathing parameters for nebuliser testing?

Tidal volume, breaths per minute, inhalation/exhalation ratio.

Why is aerodynamic particle size critical?

Determines where particles deposit in the respiratory tract.

What happens to particles <1μm?

Likely exhaled without deposition.