Inhalation therapy for respiratory diseases (Proceedings)
The use of inhaled medications is certainly not a new phenomenon in feline medicine. It makes intuitive sense that local delivery of medication might result in different actions than systemic administration. There are two primary methods for delivering inhaled medications to cats: 1) use of metered dose inhalers (MDI) or 2) use of a nebulizer to aerosolize liquid medications.
This main focus of this talk will be to cover the primary indications, clinical use considerations, contraindications, and side effects of medications commonly delivered to cats via MDI, but there will be some brief discussion of nebulization therapy as well.
General information about MDI deliveryWhy use inhalation therapy?
One of the most commonly cited reasons for recommending inhaled medications as an alternative to oral/systemic medications is the lack of systemic absorption. Since less (not zero) medication is absorbed, there may be fewer systemic side effects, interactions with other medications, or problems with other co-morbid conditions. Another way to look at this is that if the medication is only needed in the airway, why deliver it to the whole body. In theory it may also be possible to deliver a concentration of medication to the airway that would be impossible to achieve with systemic administration due to other effects of the medication.
Another common reason for using an inhaled medication is that there may be a more rapid onset of action for certain medications. This is certainly not true for all inhaled medications, however, so it is important to be familiar with the specific medications you prescribe.
One final reason for utilizing this method of delivery is that there are certainly patients for which attempts to administer oral medications on a long term basis is impractical, impossible, or detrimental to the human-animal bond between the cat and client.
Delivery of medication
Effective use of a MDI in adult humans requires coordination between device actuation and inhalation. Since this is essentially impossible to achieve in cats (as with small children), an alternative method of delivery is needed that eliminates the need for such coordination. One method that has been developed involves the use of a spacer device which serves as a reservoir for the medication after actuation so that it can then be inhaled by the cat. When using this type of device, the amount of drug that is actually delivered to the lower airways is dependent on a number of factors such as the length, diameter, and total volume of the entire spacer apparatus (MDI, spacer, mask). The Aerokat® brand spacers seem to have appropriate characteristics for delivery of most commonly used MDI products for the average cat and a study utilizing radiolabeled aerosolized particles administered via a spacer device was able to demonstrate that the particles did reach the lower airways.
Even with a spacer, it is still important to follow a consistent protocol for administration of the MDI medications. The MDI should be shaken before use to open an internal valve, then attached to the spacer apparatus. The mask on the other end of the apparatus is then placed over the muzzle of the cat (covering both nose and mouth) before the device is actuated. After actuation, the cat should take 7-10 full breaths before removing the apparatus.
Some medication will settle out or stick to the sides of the spacer apparatus, so it is a good idea to rinse the spacer out regularly. As long as it is cleaned, one spacer can be used for multiple medications (e.g. a steroid and a bronchodilator).