Hydration
Saline nasal drops--can be used as needed to better hydrate nasal tissues.
Humidifiers--an important consideration especially in colder climates when dry heat is used. Humidifiers in general cover 200-300 ft2 of living space and this should be kept in mind when deciding how many humidifiers to use in a home.
Nebulisers--these generate water particles <5 µm in diameter. In theory, smaller particles should reach deeper surfaces within the respiratory tract. In reality, most inhaled moisture condenses on the back of the pharynx and never reaches past the first-generation bronchi. For this reason, humidifiers serve essentially the same purpose as more expensive nebulisers and are preferred.
Decongestants/ Expectorants
Decongestant nasal drops can be used twice daily for 3 days at a time safely without causing a rebound vasoconstriction ('addiction' to nasal spray). This may be repeated by skipping 3 days, then using every 3 days as needed on a chronic basis.
Systemic decongestants--the author has not found these to be helpful in veterinary patients.
Guaifenesin--this is marketed under many trade names. It has been available since 1826. In theory, it probably stimulates a 'gastropulmonary' vagal reflex and is meant to increase the fluid nature of mucus so that it can more easily be coughed up into the oropharynx. It may play a small role in assisting the clearance of mucus in acute infections like herpesvirus infections in cats and Bordetella (kennel cough) infections in dogs. It is not helpful for clearing the mucus that occurs in chronic disorders such as chronic bronchitis in dogs or bronchitis or asthma in cats.
Antihistamines
The most common antihistamine used in canine medicine is diphenhydramine. This is used most often in veterinary dermatology. Antihistamines work by blocking the action of histamine, a preformed chemical mediator found primarily in mast cells. Mast cells in the skin are connective tissue mast cells, while mast cells in the airways are mucosal mast cells. This is important because the biological behaviour of these two subsets of mast cells is not the same. As a result, diphenhydramine is not usually the most effective antihistamine for dogs with respiratory allergy. In the author's experience, the drug clemastine is more effective. A recent pharmacokinetic study in dogs suggested a dose of 0.5 mg/kg orally q12h.
Histamine is not the primary preformed mediator in feline mast cells; the primary mediator in this species is actually serotonin. The most commonly used antihistamine in this regard is cyproheptadine, usually given at 2 mg orally q12h to the average 4-5 kg cat.
There are many antihistamines available to treat humans. This is due, in part, because some work better for some people, while different antihistamines work better for others. The same principle is probably true in dogs and cats and a bit of trial and error may be required before the most effective antihistamine is found for the individual patient.
Antibiotics
In an ideal world the choice of antibiotics is made on the basis of culture and sensitivity data. In most cases, however, this is neither required nor realistic. Most bacterial infections of the respiratory tract in dogs and cats are caused by the same species of bacteria, including Staphylococcus, Streptococcus, Escherichia coli, Bordetella and Pasteurella. When bacterial infections of the trachea, bronchi or lung are diagnosed, the commonly used antibiotics are usually quite effective, with consideration for the issues listed below:
It is important to recall that there exists a 'blood-bronchus' barrier that prevents adequate penetration into the bronchi by many common antibiotics, including most penicillins and cephalosporins.
Additionally, in cases of pneumonia or lung abscess, there is often a mixed infection including anaerobic bacteria. Fluoroquinolone drugs, for example, do not kill anaerobic bacteria.
In dogs, the most common bacterial infection of the respiratory tract is Bordetella, part of the 'kennel cough' complex. The author usually uses an antibiotic in this setting if the patient has a green/ yellow discharge or if the patient is acting unwell. When choosing an antibiotic it is valuable to recall that in young dogs, tetracycline-type drugs may cause staining of enamel. Fluoroquinolone drugs may theoretically cause disruption of normal cartilage formation.
In cats, the most common bacterial infection is within the nose and nasopharynx as part of an upper respiratory viral infection. In this setting, the 'normal' commensal bacterial flora (that we, dogs and cats breathe every day) are able to penetrate the diseased nasal and sinus mucosa and cause a true infection. Most antibiotics are effective initially in this setting. Remember that fluoroquinolones in general, and enrofloxacin specifically, are associated with retinal damage if given at more that the recommended dose of 5 mg/kg orally q24h.
Corticosteroids
Corticosteroids are important drugs to use in many pathological conditions of the respiratory tract in dogs and cats.
Injectable--the injectable corticosteroids are usually given in the form of a 'repository'. The most common drug used in this class is methylprednisolone acetate. This method of drug administration delivers a supraphysiological dose of steroid that slowly gets metabolised over weeks. This is helpful for patients that absolutely cannot tolerate oral or inhaled medications (see below). However, frequent use of repository-type corticosteroids is most commonly associated with severe side effects including diabetes and diabetes-like conditions. For this reason, it is the least preferred method of treating veterinary patients with this class of drug
Oral--this is the most common method of delivering this class of drugs to our patients. The advantage is that a proper daily dose of medication is delivered. Prednisone and prednisolone are the most common types of this drug. These drugs are very potent medications, and, like the injectable corticosteroids, can still cause severe side effects including diabetes
Inhaled--the most commonly used inhaled steroid is fluticasone. The primary advantage to using this drug is that it is not well absorbed into the blood stream and does not, in general, cause systemic side effects even when administered for months or years. Almost all dogs and most cats can be easily acclimatised to this form of drug administration by using a 'spacer' and mask fitted to their face or muzzle
More specific drug names and dosages/side effects will be listed in relation to specific diseases that will be discussed in the course of the lecture.
References
1. Hansson H, Bergvall K, Bondesson U, Hedeland M, Törneke K. Clinical pharmacology of clemastine in healthy dogs. Veterinary Dermatology 2004; 15: 152-158.