Respiratory System Drugs Overview

Respiration is the exchange of gases between the atmosphere and the cells of the body. Ventilation is bringing fresh air in.
Upper respiratory tract includes nares, nasal cavity, pharynx, larynx, and trachea
- Lined with epithelial cells containing cilia
- Cough receptors mainly found in the pharynx and trachea. Suppresses non-productive coughs.
- Diseases: congestion, sneezing, and coughs.
Lower respiratory tract includes trachea, bronchi, bronchioles, and alveoli.
- Bronchioles have smooth muscle
- Sympathetic stimulation = bronchodilation (relaxation of muscle)
- Parasympathetic stimulation = bronchoconstriction (contraction of muscle).
- Alveoli produce surfactant to keep them open by reducing surface tension
- Diseases: asthma, bronchitis, pneumonia, recurrent airway obstruction ("heaves" in horses).
Respiratory Drugs
- Expectorants: increase respiratory secretions to allow material to be coughed up; increase mucus fluidity. Example: Guaifenesin
- Adverse Effects: mild decrease in blood pressure (BP) and increased heart rate (HR).

Decrease the viscosity (thickness) of respiratory secretions. Example: Acetylcysteine
Adverse Effects: vomiting, hives (rarely), potential chest tightness, irritation.

Suppresses coughs (productive or not usually suppressed).
Can be centrally acting (brain stem) or locally acting (mucosal linings).
Central acting antitussives can cause respiratory depression. Examples: opioids (Butorphanol, hydrocodone, codeine), Dextromethorphan.

Widen the lumen of the bronchi (widening the airways).
Example: Stimulation of Beta-2-adrenergic-agonists which are involved in bronchodilation. and stabilization of mast cells. (Epinephrine, isoproterenol, Terbutaline, albuterol)
Methylxanthines: Inhibit an enzyme in smooth muscle. Examples include Aminophylline & theophylline.
Adverse effects: Nausea, vomiting, CNS stimulation (increased heart rate, etc.)
Antihistamines block H1 receptors to reduce bronchoconstriction, increased HR, vasodilation, CNS sedation, and inflammatory response. Examples: Diphenhydramine & chlorpheniramine.
Adverse effects include: CNS depression, dry mouth, and urinary retention.

Asthma (feline) - chronic inflammatory disease of lower airways caused by inhaled allergens causing smooth muscle contraction.
Recurrent Airway Obstruction (ROA): treated by maintaining horses in a good environment and medication.
Infectious Tracheobronchitis (Kennel cough)

Hormones are chemical messengers produced by cells in one part of the body and transported to another part. Endocrine glands involved: pituitary, thyroid, parathyroids, adrenal, pancreas, thymus, pineal, gonads.
Hormones are regulated via feedback loops
Some drugs can replace or increase/decrease hormone production.

Pancreas secretes insulin and glucagon to regulate blood glucose levels.
Insulin helps increase the uptake and use of glucose by cells.
Glucagon promotes glycogen breakdown to increase blood glucose levels.
Hypoglycemia is low blood glucose- treated by reducing symptoms and avoiding hypoglycemia.

Short-acting, Intermediate-acting, Long-acting, Ultra-long-acting. Work on maintaining stable blood sugar.
Oral hypoglycemic agents work by stimulating pancreatic beta cells to secrete insulin.
Examples of oral hypoglycemic agents include Glipizide, and others.

Kidneys: filtration of blood, reabsorption of essential substances, and secretion of waste products.
Glomerulus filters substances out of the blood.
Tubules reabsorb needed substances, or excrete substances back into plasma. Substances filtered include: water, glucose, amino acids, ions.
Waste products are part of urine.
Disorders: UTI's, renal failure, urolithiasis, feline lower urinary disorders, urinary bladder cancer, bacterial infections, etc.

Diuretics: increase urine volume (e.g., Loop diuretics, Potassium-sparing diuretics, Thiazides, carbonic anhydrase inhibitors, Osmotics); these function in different parts of the nephron to eliminate excess water.
Urinary acidifiers modify pH to treat stones in the urinary tract.
Urinary alkalinizers raise urine pH to treat some types of stones.