MDI are designed for at-home administration of aerosolized drugs and are the preferred routine route of delivery for glucocorticoid
and bronchodilator medications in people with asthma. Particles delivered by MDI are larger than those created by nebulization,
and thus do not penetrate as deeply into the respiratory tract. A traditional MDI consists of a mouthpiece and an actuator
(holder) into which a canister of medication is inserted. Manually depressing the canister (actuation) results in the release
of a single dose of medication (sometimes called a puff). People shake the canister, exhale deeply, insert the mouthpiece,
and simultaneously depress the canister and inhale as deeply as possible. They then hold their breath for as long as possible,
exhale and rinse the mouth and spit to remove the majority of the drug deposited in the oropharynx (only about 10 percent
of each dose reaches the airways). Obviously, dogs and cats can't use an MDI in this way. Spacers devices designed to fit
the MDI have allowed their adaptation for use in animals. Several types of spacers are available, from simple tubes inserted
between the MDI and the mouth and nose to holding chambers with one-way valves activated by inhalation.
Spacers were designed for young children or others with less than ideal coordination so that there is no requirement for simultaneous
depression of the canister and inhalation. The spacer also has the advantage of allowing the largest particles to fall out
and not enter the individual's mouth.
Until recently, most MDI used chlorofluorocarbons as propellants. Concerns about the ozone layer have led to new technologies,
including alternate propellants and the use of dry powder inhalers (DPI). The DPI devices contain no propellant, but rely
on the individual's inhalation through a reservoir containing a dry powder dose. The most common types of DPIs are discus
inhalers and turbohalers. Because they do not use a spacer device and require a voluntary inhalation of a minimum force to
deliver drug, these devices may be less useful for dogs and cats than MDI attached to spacers.
Indications for nebulization
Nebulizers have long been used to provide airway humidification or to administer antimicrobials directly into the respiratory
tract. Mucolytic agents (e.g., N-acetylcysteine) have also been nebulized to treat animals with respiratory infection. Sterile
saline nebulization without antimicrobial drugs for 15-30 minutes at a time, administered three to four times per day is safe
for the treatment of animals with bronchopneumonia.
It is common to include antimicrobials in nebulized solutions to treat severe bacterial pneumonia. There are drugs made especially
for delivery by this route that do not contain potentially reactive additives or preservatives (e.g., Tobi®) but these preparations
are prohibitively expensive.
Veterinarians have used inexpensive drugs made for parenteral administration in nebulized solutions for the treatment of pneumonia
or other respiratory infections, including Bordetella bronchiseptica. Not all liquid antibiotics would be suitable for nebulization.
The most frequently used class of antibiotics for nebulization is the aminoglycosides.
There are no well-established guidelines for dosing or administration of formulations of drugs not made for aerosol use in
dogs and cats. Typically, the dose that would be used systemically of a drug such as gentamicin or amikacin is diluted in
saline to be delivered over a single 15-30 minute session with the nebulizer. It should be expected that a small percentage
of animals may experience bronchoconstriction in response to such therapies.
Pretreatment with bronchodilators may minimize potential reaction to drug carriers and improve drug delivery by the aerosol
route. Bronchodilators may be administered by parenteral routes 15 minutes prior to nebulization or via an initial period
of nebulization with the bronchodilator added directly to the nebulized fluid before the addition of the antimicrobial drug.
Delivery of antimicrobials should not replace systemic antimicrobials in animals with pneumonia. Instead, regard it as a complimentary
When nebulizers are used in the treatment of dogs and cats with contagious respiratory disease, the device itself must be
kept meticulously clean to avoid causing iatrogenic respiratory infection. Extreme care should be given to cleaning, and disposable
parts of the device should be disposed of after use in animals with respiratory tract infection. Nebulization of a nosocomial
Pseudomonas species, for instance, could have devastating consequences for an animal with compromised respiratory function.
Indications for MDI
Metered dose inhalers (MDI) are the preferred route of delivery for most asthma medications in people, and they have been
advocated for the treatment of feline bronchopulmonary diseases including asthma as well as for the treatment of dogs with
chronic bronchitis or related airway disease.