Inhalation therapy has been used for many years, and there has been a resurgence of interest in delivery of drugs by this route of administration. The number of new drug entities delivered by the inhalation route has increased over the past five to ten years.
This type of therapy also has been applied to delivery of drugs through the nasal mucosa, as well as through the oral cavity for buccal absorption. Originally, this type of therapy was used primarily to administer drugs directly to the respiratory system (treatment of asthma); inhalation therapy is now being used for drugs to be delivered to the bloodstream and finally to the desired site of action. Proteins (insulin), steroids, cardiac agents, immunizing agents, etc., are being developed for delivery in this manner.
Drugs administered via the respiratory system (inhalation therapy) can be delivered either orally or nasally. Further, these products can be developed as a
- nebulizer/atomizer
- dry powder inhaler
- nasal inhaler
- metered-dose aerosol inhaler
Dry powders have been used for inhalation therapy for over 75 years. The active ingredients were packaged in capsules, representing a single dose of drug. The capsule was punctured, and a small amount of powder fell into a chamber while the patient inhaled.
Metered-dose inhalers consist of a pressurized container filled with active ingredient, excipients and propellant, and a metered-dose valve. The pressurized container is placed within an oral adapter (mouthpiece), and when the unit is dispensed, an exact amount of drug is expelled in the proper particle size distribution to achieve maximum deposition of drug into the lungs. The aerosol dosage form (MDI) has become the dosage form of choice for delivery of drugs to the lungs. Metered-dose inhalers are formulated as solutions or suspensions of active drug in a mixture of solvents, dispersing agents, and liquefied gas propellants.