Anti-Asthma Drugs

Drug Delivery

• Preferred mode of delivery of many drugs with a direct effect on airways, particularly for asthma and COPD
• Only way to deliver some drugs such as cromolyn sodium and anticholinergic drugs
• The preferred route of delivery for beta-2 agonists and corticosteroids to reduce systemic side effects, as well as reducing onset of action
• Inhalation is also used to facilitate systemic drug delivery in other diseases eg. insulin in diabetics
• Particle Size is of critical importance in determining the site of deposition in the respiratory tract

• Optimal size for inhaled particles to settle in airways is 2-5μm
• Larger particles are deposited in upper airways, while smaller particles remain suspended and are exhaled

• Only 10-20% of total drug delivered enters lower airways with a conventional MDI
• Drugs act directly on target cells in the airway, as well as being absorbed into bronchial circulation to act more distally on peripheral airways
• Pressurised MDIs: HFA propellant, required coordination of inhalation with device activation
• Spacer Chambers: Reduce the velocity of particles entering the upper airways and the size of the particles by allowing propellant to evaporate

• Reduces drug deposition onto oropharynx and therefore reduction of local side effects - especially corticosteroids
• Does not require inhalation coordination - can be used in young children

• Dry Powder Inhalers:

• Scatter a fine powder dispersed by air turbulence on inhalation.. Can cause airway irritation.

• Nebulisers:

• Either jet (driven by stream of gas) or ultrasonic (driven by rapidly vibrating piezo-electric crystal)
• The drug is inhaled during normal tidal breathing, therefore much higher doses can be delivered
• Useful in acute illness, small children, extreme airway obstruction

• Oral Administration:

• 20x more medication required for oral dosing.
• Theophylline is ineffective when inhaled and must be given orally/IV
• Corticosteroids may also have to be given orally/IV

Bronchodilators

• β2 adrenergic agonists - most widely used bronchodilators as they are the most effective and have minimal side effects