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Drugs Used to Treat Lung and Airway Disorders

By Philip T. Reeves, BVSc (Hons), PhD, FANZCVS, Chief Regulatory Scientist, Veterinary Medicines and Nanotechnology, Australian Pesticides and Veterinary Medicines Authority ; Dawn Merton Boothe, DVM, PhD, Professor, Department of Anatomy, Physiology, and Pharmacology, College of Veterinary Medicine, Auburn University ; Maya M. Scott, BS, DVM, Resident, Clinical Pharmacology, Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Texas A&M University ; Ian Tizard, BVMS, PhD, DACVM, University Distinguished Professor of Immunology; Director, Richard M. Schubot Exotic Bird Health Center, Department of Veterinary Pathobiology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University ; Jozef Vercruysse, DVM, Professor, Faculty of Veterinary Medicine, Ghent University ; Jörg M. Steiner, DrMedVet, PhD, DACVIM, DECVIM-CA, AGAF, Associate Professor and Director, Gastrointestinal Laboratory, Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A & M University

Drugs used to treat respiratory conditions fall into several categories: cough suppressants, bronchodilators, expectorants, and decongestants. Antibiotics and anti-inflammatory drugs are also important in the treatment of many respiratory diseases.

Cough Suppressants

Cough suppressants stifle the coughing reflex. Most cough suppressants are narcotics that act directly on the part of the brain that prompts coughing, the medulla oblongata. Morphine is an effective cough suppressant at doses lower than those used to control pain or sedate. However, it is not commonly used because of its side effects. Codeine is found in many preparations, including tablets, liquids, and syrups. Hydrocodone is similar to codeine but is stronger. It is combined with an anticholinergic drug to discourage abuse by people. Dextromethorphan is not technically an opioid because it does not behave in the same way in the body and is not addictive or analgesic. Butorphanol is used as a painkiller and cough suppressant.

When prescribing a cough suppressant, your veterinarian will take into consideration the fact that some are not safe for use in cats. You should never give over-the-counter preparations intended for human use to your pet unless directed by a veterinarian.

Bronchodilators

In certain airway disorders, breathing becomes difficult because the muscles surrounding the airways constrict. Bronchodilators relieve this constriction by relaxing the muscles, which opens the airways and allows air to move more easily in and out of the lungs. Bronchodilators may also help relieve inflammation and clear mucus from the lungs. There are several categories of bronchodilators.

The beta-adrenergic agonists have beneficial effects in the treatment of bronchoconstrictive airway diseases. These have been shown to relax the bronchial smooth muscle, decrease the inflammatory response in the airways, and help the cilia clear mucus from the respiratory tract.

The methylxanthines are also used as bronchodilators. They cause relaxation of the bronchial smooth muscles, stimulation of the central nervous system, and mild heart stimulation. Methylxanthines also decrease the inflammatory response in the airways and help the cilia clear mucus from the respiratory system.

Anticholinergic drugs are effective bronchodilators that act by reducing the sensitivity of irritant receptors and inhibiting smooth muscles in the respiratory tract.

Anti-inflammatory Drugs

Glucocorticoids (a type of corticosteroids) help control inflammation of the airways by preventing the body’s release of inflammatory chemicals. Because they suppress the immune system, glucocorticoids are generally not used in treating infectious respiratory diseases. In cases of severe attacks of allergic bronchitis, asthma, or recurrent airway inflammation, injection of glucocorticoids usually provides rapid relief. For longterm treatment in dogs and cats, oral treatment is usually used.

Antibiotics

Antibiotic treatment may or may not be necessary in the treatment of inflammatory airway diseases. Antibiotics may be prescribed when a true bacterial infection is present or when infection is making existing airway disease worse.

Inhalation Treatment

With inhalation treatment, high drug concentrations are delivered directly to the lungs by nebulizers or metered-dose inhalers. This helps to avoid or minimize certain adverse effects. Also, the drug’s effects are seen more rapidly than with other delivery methods. Drugs available in metered-dose inhalers include several bronchodilators and anti-inflammatory drugs.

Expectorants and Mucus-producing Drugs

Expectorants and mucus-producing drugs make coughs more productive. They do this by increasing the amount of bronchial secretions, in addition to thinning the secretions. This clears the airways and eases breathing. They are usually given by mouth, although some can be nebulized and inhaled.

Decongestants

Decongestants, though commonly used in people to treat the sneezing and runny nose associated with allergies or hay fever, are rarely used for this purpose in animals. The alpha-adrenergic agonist drugs cause local constriction of the blood vessels, reducing swelling and edema. They can be used topically as nasal decongestants in allergic or viral rhinitis. They can also be used systemically with antihistamines as respiratory tract decongestants. Antihistamines, when combined with alpha-adrenergic agonist drugs, are effective for treatment of allergic rhinitis in humans, but the effectiveness in animals is inconsistent.