Herbs provide a number of actions that benefit both upper and lower respiratory diseases, including bronchitis (acute, allergic, and chronic), feline bronchial asthma, and sinusitis / rhinitis. Interestingly, some of the respiratory herbs are in the most commonly used, mass produced cough medicines available through pharmacies. These include cherry bark, Irish moss, and Licorice.
Several groups of herbal actions are useful in the treatment of chronic respiratory disorders, and many traditional respiratory herbs fall into more than 1 group. In terms of respiratory therapy, the major actions are as follows.
Antitussives reduce coughing either through demulcent action, by removing the irritation (expectorant) action, or by depressing the cough reflex. This group therefore includes expectorants, demulcents, and anticatarrhals. The best known antitussive herbs are Irish moss (Cbondrus crispus), Wild cherry (Prunus serotina), and Licorice (Glycyrrhiza glabra). Licorice root contains a potent antitussive compound, liquilitin apioside, the antitussive effects of which may depend on both peripheral and central mechanisms. A 50% methanol extract of licorice (100 mg / kg PO) reduced by more than 60% the number of capsaicin-induced coughs (Kamei 2003).
Marshmallow (Althaea officinalis) and Burdock (Articum lappa) may also be useful. The antitussive capacity of marshmallow extract and its isolated polysaccharide were compared with the nonnarcotic drugs prenoxdiazine and dropropizine in cats. Unanesthetized cats were stimulated to cough through nylon fiber irritation of laryngopharyngeal and tracheobronchial mucus. Tracheal pressure was measured to determine the number of cough efforts. At 50 mg / kg PO, the polysaccharide inhibited the cough; and the cough was inhibited with 1,000 mg / kg PO of althaea syrup. The whole plant extract was less effective than the polysaccharide. Burdock was also tested for antitussive activity in cats. An inulin isolate (fructan) from A. lappa roots was found to be equally active as some nonnarcotic, synthetic preparations used in clinical practice to treat cough.
Tenacious mucus can act as an airway irritant and invoke a cough reflex. Clearing mucus is a fundamental herbal principle for any respiratory disease characterized by excessive mucus production. Herbalists use expectorants to facilitate removal of secretions, either by reducing the tenacity of the mucus (catarrh), which can irritate airways, or by increasing expulsion. Expectorants are not indicated with a pharyngitis causing a cough; they are used when there is tracheal or lung involvement. They are best used for subacute or chronic inflammatory conditions. Depending on the constituents, expectorants can work by acting directly on goblet cells — these include the essential-oil-containing herbs such as Fennel (Foeniculum vulgaris) and Aniseed (Pimpinella anisum) — which might be useful if secretions are scant; by stimulating the vagus nerve and making secretions more watery — these include Lobelia (Lobelia inflate) — and by herbs that stimulate mucocil-liary transport, such as thyme (Tbytnus vulgaris).
There have been very few clinical studies on the benefits of expectorants; however, some studies show that saponin-containing herbs administered orally enhance production of respiratory tract fluid. In one study Senega root (Polygala senega) increased fluid output by 173% in cats in 3 to 4 hours. In another study the same herb caused a 10-fold increase in fluid output in dogs after 5 to 30 minutes when compared with a saline control. It should be noted that the doses used were extremely high.
Syrup of Thyme was compared to bromhexine in a double-blind, randomized study of 60 patients with productive cough, and there were no significant differences between the self-reported symptom relief. Other commonly used expectorants include Licorice (Glycyrrhiza glabra), Grindelia (Grindelia camporum), White horehound (Marrubium vulgare), Elecampane (Inula helenium), and Malabar nut tree (Adhatoda vasica). Adhatoda is a source of vasicine from which the drug Bisolvin was developed. Expectorants are commonly prescribed with spasmolytic, anticatarrhal, and immune-stimulating herbs.
This group of herbs contains mucilage constituents, which have antiinflammatory and soothing effects on the lower respiratory mucosa. They are ideal for acute coughs with very acute catarrh with inflammation and irritation. They include Marshmallow (Althaea officinalis), Irish moss (Chondrus crispus), and Slippery elm (Ulmus flava). Plantain (Plantago major), Mullein (Verbascum thapsus), Fenugreek (Trigonella foenumgraecum), and Coltsfoot (Tussilago farara) are other traditional demulcents.
Anticatarrhals reduce excessive discharge from mucous membranes. They are particularly useful for nasal and sinus congestion and mucosal edema, and they can reduce airway hypersensitivity. Anticatarrhal herbs for the upper respiratory tract include Eyebright (Eupbrasia rostkoviana), Elder flower (Sambucus nigra), Ribwort (Plantago lanceolata), Peppermint (Mentba piperita), Fenugreek (Trigonella foenumgraecum), Golden rod (Solidago spp), and Golden seal (Hydrastis canadensis). The latter two are particularly indicated for copious yellow to green discharge of a chronic nature. Sage (Salvia officinalis) has a drying effect that can be useful for copious watery discharges. Anticatharrhal herbs for the lower respiratory tract include Mullein (Verbascum thaspus) and Ribwort (Plantago lanceolata).
Respiratory spasmolytics help relax the bronchioles. These include Elecampane (Inula helenium), Lobelia (Lobelia inflata), Grindelia (Grindelia camporum), Thyme (Thymus vulgaris), Licorice (Glycyrrhiza glabra), Euphorbia (Euphorbia hirta), Celadine (Chelodium majus), and Ephedra. Lobeline, a constituent of Lobelia, induced hyperpnea due to both an increase in tidal volume and respiratory rate in ponies. Lobeline is also considered a Beta-adrenergic bronchodilator. Thymol, Carvacrol, and the essential oil from Thyme, in sufficient doses, have tracheal relaxant activity.
Most respiratory antiseptics have mild antimicrobial activity. This activity is usually related to volatile oil constituents. Steam inhalation of teas could be considered for small animals. These herbs include Thyme (Thymus vulgaris), Elecampane (Inula helenium), Garlic (Allium sativum), Hyssop (Hyssopus officinalis), Lavender (Lavendula offincialis), and Rosemary (Rosmarinus officinalis).
The main herbs for respiratory tract allergies are Albizzia (Albizzia lebbek), Baical skullcap (Scutellaria baicalensis), Boswellia (Boswellia serrata), Ginkgo (Ginkgo biloba), Malabar nut tree (Adhatoda vasica), and Nettles (Urtica spp) for allergic rhinitis. Albizzia provided excellent reponses in an uncontrolled trial of patients with asthma of recent onset (less than 2 years), but the response was less predictable for chronic asthma. Baicalin and Baicalein have demonstrated antiallergic and antiasthmatic activity in several animal models.