Antitussives

Chronic coughing can impact a pet’ s quality of life. Although a number of antitussive drugs and strategies exist, management can be frustrating due to inconsistent efficacy, which can reduce further over time.

Other issues include adverse effects, cost of medication, and availability. A perfect antitussive drug does not yet exist and medications targeting new pathways and receptors are under development.

Cough Physiology:

Coughing is a complex involuntary reflex in dogs and cats triggered by chemical, mechanical or inflammatory stimuli. Cough receptors are located in the larynx, trachea and bronchi (but not the smaller bronchi, bronchioles or alveoli).

Is an Antitussive Indicated?

Although a cough is a protective mechanism, chronic coughing can promote airway inflammation and damage, as well as impairing quality of life and sleep if uncontrolled. Care must be taken not to suppress a beneficial cough. In general, antitussives are most appropriate if a cough is chronic (present for more than two months) and unproductive. Before prescribing, we should ask:

• Are antitussives contraindicated? Examples include a productive cough, an infectious cause, inhalation of foreign material, or significant central nervous system depression.
• Would better control of the cough be achieved through medication directly targeting the underlying cause/condition?
• Have potential adverse effects been considered?

Antitussive Medications:

Antitussive drugs currently available are broadly divided into opioid and non-opioid groups. Opioids are generally the most effective and are used most widely for dogs. Adverse effects (constipation, sedation, respiratory depression, possibly excitement) are encountered more commonly in cats, therefore non-opioids (e.g. dextromethorphan) have been suggested to be most appropriate in this species (Hsieh and Beets 2020).

Other strategies:

Changes to a pet’ s environment (including reducing exposure to allergens, dust or smoke), gentle exercise and nebulisation may help to alleviate coughing. Bronchodilator, anti-inflammatory and anti-histamine medications can reduce coughing in some settings. As respiratory secretions may be viscous, mucolytics and expectorants may aid clearance by the mucociliary escalator.

Emerging options:

There is some evidence to support antitussive effects of medications currently licensed for other uses. A recent study demonstrated antitussive activity of maropitant in dogs with chronic bronchitis (Grobman and Reinero 2016). Gabapentin has shown benefits for chronic idiopathic cough in people but has not yet been studied in dogs or cats. Novel antitussive drugs of multiple classes are also under development (NOP agonists, TRPV1 antagonists, TRPA1 antagonists, erdosteine, naringin, and cannabinoid agonists) and may improve our ability to manage chronic coughing in our patients (Hsieh and Beets 2020). Respiratory secretions may be viscous, mucolytics and expectorants may aid clearance by the mucociliary escalator.

References

Grobman, M. and Reinero, C. (2016), Investigation of Neurokinin‐1 Receptor Antagonism as a Novel Treatment for Chronic Bronchitis in Dogs. J Vet Intern Med, 30: 847-852

Hsieh B. and Beets, A. (2020), Coughing in Small Animal Patients. Front Vet Sci, 6:513

Reinero, C. Lee-Fowler, T. Dodam, J. Cohn, L. DeClue, A. Guntur, V. (2011), Endotracheal nebulization of N-acetylcysteine increases airway resistance in cats with experimental asthma. J Feline Med Surg, 13(2):69-73

Rozanski, E. (2014), Canine chronic bronchitis. Vet Clin North Am Small Anim Pract, 44(1):107-16

Church, D. (2006), Drugs Used in the Management of Respiratory Diseases. WSAVA World Congress Proceedings