Aerosols are used to deliver active drugs to the pulmonary airways, the nasal passages, or the oral cavity. They are also used to administer drugs topically and into body cavities such the vagina and rectum.Pulmonary, nasal, and oral administration is intended to achieve either local or systemic therapeutic effect, while topical, vaginal, and rectal administration is only intended for local effect.
Inhalation therapy (i.e., drug delivery to the pulmonary airways and nasal passages) was once accomplished using nebulizers or atomizers that were cumbersome to use and restricted to institutional or home use. The development of the metered dose inhaler in the mid 1950s provided the convenience of portability with the accuracy of dosing.
Successful inhalation therapy requires that the formulation emit droplets or particles that are the optimum size. Large particles (about 20 µm) deposit in the back of the mouth and throat and are eventually swallowed rather than inhaled. Particles in the 1 to 10 µm range will reach the bronchioles. Very small particles (0.6 µm) penetrate to the alveolar sacs but have limited retention since a large fraction of the particles are exhaled in the breath. The most therapeutically effective particle size range appears to be between 3 and 6 µm Therefore, it is
important that the aerosol system produce most of its particles between approximately 1 and 10 µm.
MDIs are the most commonly used product for inhalation therapy and is also one of the most difficult dosage forms to administer properly. One of the most critical maneuvers during administration is to coordinate the actuation of the aerosol with the patient's inspiration. The mouthpiece adapter on the aerosol package has been repeatedly modified since the mid 1970s in an attempt to help patients receive the correct dosage when this coordination is not performed correctly. Larger adapters (sometimes called tube spacers) permit the propellant to completely evaporate before the aerosol reaches the patient. This results in a reduced particle size and velocity. The reduced particle size improves the depth to which the drug will penetration into the lungs and the lower velocity decreases the amount of drug that will impact on the back of the throat. The biggest disadvantages of these larger adapters are the cost, difficulty to clean, and inconvenience to use because of their size.
Nasal aerosols deliver the drug directly to the nasal mucosa. The most common nasal aerosols contain steroids used to treat nasal congestion, sneezing, and running nose associated with hay fever, allergies, and rhinitis. Such products use steroids such as beclomethasone dipropionate, triamcinolone acetonide, dexamethasone sodium phosphate, and budesonide. Aerosols used to deliver drugs to the oral cavity generally administer the product sublingually. One such product is a sublingual nitroglycerin formulation that is sprayed under the tongue and delivers 0.4 mg of nitroglycerin per actuation.
Topical aerosol formulations are available for local anesthetics, antiseptics, germicides, first aid preparations, and spray on protective films. These aerosol deliver particles that are larger and more course than the inhalation aerosols. Topical aerosols deliver the active drug in the form of a powder, a wet spray, a stream of liquid, or an ointment like product.
Vaginal and rectal foams are available that contain estrogens, contraceptives, and anti-inflammation agents. These products are packaged in containers that have an application device which is filled with foam when the valve is actuated and then the device is placed in the vagina or rectum and the foam is instilled with the device plunger.