4.2 nebuliser medicines

Medications delivered via nebulizers are typically formulated as solutions or suspensions. Key formulation factors include:

solubility

isotonicity

pH stability

preservatives

Solubility:

Medications must be soluble in water or a suitable solvent.

Isotonicity:

Solutions are adjusted to match the osmolarity of bodily fluids to avoid irritation.

pH Stability:

Formulations are buffered to maintain a pH > 5 to prevent bronchospasm.

Preservatives:

Unit-dose vials often avoid preservatives to reduce the risk of irritation and hypersensitivity.

Suspensions require careful particle size optimization (2-5 μm) to ensure effective deposition.

Mesh nebulizers are particularly suited for delivering suspensions,

while ultrasonic nebulizers may cause issues like aggregation or thermal degradation.

The physicochemical properties of nebulizer fluids significantly influence their performance and patient outcomes. Important considerations include:

viscosity

surface tension

temperature effects

residua volume

Viscosity: Higher viscosity increases the energy required for nebulization. Jet and mesh nebulizers show an inverse relationship between viscosity and droplet  size, while ultrasonic nebulizers exhibit a direct relationship.

Surface Tension: Lower surface tension reduces droplet size, improving drug deposition in the lungs. Formulations are designed to balance surface tension to optimize aerosol characteristics.

Temperature Effects: Jet nebulizers cause a temperature drop of approximately 10–15 °C during operation, potentially affecting drug solubility and viscosity. This cooling effect is less pronounced with mesh nebulizers and is reversed in ultrasonic nebulizers, which may increase the solution      temperature by up to 15 °C.

Residual Volume: The volume of liquid left in the nebulizer after treatment, termed the 'dead volume,' varies by device type. Jet and ultrasonic nebulizers typically leave about 1 mL, while mesh nebulizers minimize this to enhance delivery efficiency.