Inhalant therapy: Finding its place in small-animal practice - Veterinary Medicine
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Inhalant therapy: Finding its place in small-animal practice
A variety of drugs are available for inhalant delivery in people. But a shortage of studies on this unique route of administration in pets leaves many questions about its role in practice. Here is a quick look at the current knowledge and applications of inhalant therapy in pets.


VETERINARY MEDICINE


WHEN AND HOW TO USE NEBULIZATION

Indications

In small-animal medicine, nebulizers have predominantly been used to treat respiratory infections. Nebulizers have long been used to humidify the airway or administer antimicrobials directly into the respiratory tract. Mucolytic agents (e.g. N-acetylcysteine) have also been nebulized to treat animals with respiratory infection but are not generally recommended because of irritation and bronchoconstriction after such therapy.3 Sterile saline nebulization administered three or four times a day is safe to treat animals with bronchopneumonia. Although no scientific studies demonstrate utility, it is my impression that saline nebulization is beneficial.

In people, it is common to include antimicrobials in nebulized solutions to treat severe bacterial pneumonia, particularly in patients with compromised defenses such as patients with cystic fibrosis.4 Some drugs that are made especially for delivery by this route do not contain potentially reactive additives or preservatives (e.g. tobramycin inhalation solution [Tobi—Novartis]), but these preparations are prohibitively expensive for dogs and cats. Veterinarians have used drugs made for parenteral administration in nebulized solutions to treat pneumonia or other respiratory infections, including infection with Bordetella bronchiseptica. Not all liquid antibiotics are suitable for nebulization. Aminoglycosides are the most frequently used class of antibiotics for nebulization.

Dosing

There are no well-established guidelines for dosing or administering drugs not made specifically for aerosol administration in veterinary patients. Typically, the total daily systemic dose of a drug such as gentamicin or amikacin is diluted in saline solution to be delivered in a single daily session with the nebulizer.

Rarely, patients may experience bronchoconstriction in response to such therapies. Pretreatment with bronchodilators may minimize potential reaction to drug carriers and improve aerosolized drug delivery. Bronchodilators may be administered parenterally 15 minutes before nebulization or by an initial nebulization period, with the bronchodilator added directly to the nebulized fluid before the antimicrobial drug is added. Common bronchodilator choices for nebulization are albuterol 0.5% solution for inhalation (5 mg/ml) or the premixed 2.5 mg/3 ml solutions. The concentrated drug should be diluted in about 3 ml sterile saline solution before administration. While a dose has not been established for nebulized albuterol in dogs and cats, the dose for children is 0.1 to 0.15 mg/kg with a maximum dose of 2.5 mg given up to a maximum of four times daily. Delivery of nebulized antimicrobials should never replace systemic antimicrobials in animals with pneumonia. Instead, nebulization should be regarded as a complementary therapy.

Prevent iatrogenic infections

When nebulizers are used to treat pets 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 discarded. Nebulization of a nosocomial Pseudomonas species, for instance, could have devastating consequences for an animal with compromised respiratory function.

WHEN AND HOW TO USE MDIS

Indications

MDIs are the preferred delivery device for most asthma and COPD medications in people, and they have been advocated for use in treating feline bronchopulmonary diseases, including asthma, as well as for treating chronic bronchitis or related airway disease in dogs.

The use of inhaled corticosteroids may be particularly helpful in minimizing the systemic effects of glucocorticoids in asthmatic cats with comorbid conditions such as diabetes mellitus or congestive heart failure. For any patient, concomitant use of inhaled and systemic corticosteroids may allow decreased systemic drug dosages. Keep in mind that inhaled corticosteroids take days or weeks to be maximally effective and, thus, should not be relied on for emergent treatment of asthmatic cats.

Albuterol delivery by MDI can be useful during exacerbations of asthma but will not always successfully replace parenteral administration of bronchodilators for cats in asthmatic crisis.

A variety of respiratory drugs are available as MDIs, including corticosteroids (e.g. fluticasone [Flovent—GlaxoSmithKline]), short-acting bronchodilators (e.g. albuterol [Ventolin—GlaxoSmithKline; Proventil—Schering-Plough]), and nonsteroidal anti-inflammatory drugs such as cromolyn or nedocromil. Some inhaled medations—including most long-acting bronchodilators and combination corticosteroid/bronchodilators (e.g. salmeterol [Serevent—GlaxoSmithKline], fluticasone and salmeterol combination [Advair—GlaxoSmithKline], formoterol [Foradil—Schering-Plough])—come as breath-actuated inhalers instead of MDIs and are, thus, not useful in dogs and cats. Even when the drug is available as an MDI, not all MDIs fit the spacers typically used for dogs and cats. For example, triamcinolone acetonide (Azmacort—Abbott Laboratories) has a built-in spacer, so it cannot be adapted to commercial feline spacer devices. Be certain that the drug you prescribe comes in an MDI that will work with the spacer device used by the client.

Dosing

To administer a dose, turn the animal so that its head faces away and its tail faces into the person delivering the drug. Shake the MDI and fit it into the spacer device, fit the mask at the other end of the spacer device over the animal's face, and depress the canister (Figure 3). When using some types of valved spacers, you can depress the canister immediately before placing the mask if the noise scares the pet. Then allow the animal to breathe into the mask for seven to 10 breaths. In my experience, few owners have trouble administering the inhaled medication in this fashion.

Appropriate dosage regimens have not been clearly established for drug delivery by MDI in dogs and cats. Commonly used medications include albuterol (108 μg albuterol sulfate/puff) for acute signs of bronchoconstriction. A single puff may be effective, or it can be given up to four times daily during an acute exacerbation. More than occasional use of albuterol can lead to paradoxic bronchoconstriction, and the need for frequent treatment (> three times a week) should prompt re-evaluation of other aspects of treating the disease.5 The most commonly used MDI corticosteroid is fluticasone propionate, available in 44-, 110-, and 220-μg/puff strengths. Although no evidence demonstrates the most effective dose, it is often used in the 110- or 220-μg strength as one puff twice daily.


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Source: VETERINARY MEDICINE,
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