Antitussives, Expectorants and Mucolytics: Pharmacology Explained
Antitussives, Expectorants and Mucolytics
Antitussives
Opioid antitussives: with opioid activity: codeine (analgesic action, sedation). Without opioid activity: dextromethorphan, pholcodine (no analgesic effect).
Benzylisoquinoline alkaloids: noscapine (used as antitussive only).
Others: cloperastine.
Expectorants
Tyloxapol (mechanism of elimination: stimulates bronchial secretions).
Mucolytics
N-acetylcysteine, S-carboxymethylcysteine, ambroxol, dornase alfa (decrease mucus viscosity, bronchial sputum secretion, and facilitate removal; dornase alfa is used in cystic fibrosis).
Cardiovascular Agents
With AP action: Glycosidic cardiotonics (inhibit Na+/K+ ATPase, so intracellular sodium rises, calcium entry increases and cardiac contractility is enhanced; their interplay with potassium modifies muscle contractility and bioelectrical activity, with effects on pressure and diuresis).
- Digoxin (oral and IV; causes blurred vision, anorexia, gynecomastia, galactorrhea and psychiatric alterations; used in the treatment of acute and chronic heart failure).
- Digitoxin (oral and IV; excretion is renal).
Antiarrhythmics
- Group 1 (sodium channel blockers): quinidine, procainamide and disopyramide, lidocaine, phenytoin and mexiletine (these three only IV).
- Group 2 (beta-adrenergic blockers): esmolol (IV; used for ventricular rate control), propranolol (short half-life).
- Group 3 (potassium channel blockers that prolong action potential duration): amiodarone (broad-spectrum antiarrhythmic; ventricular arrhythmias), dofetilide, sotalol (ventricular arrhythmias and atrial fibrillation).
- Group 4 (calcium channel blockers): diltiazem, verapamil.
- Group 5 (other agents): digoxin and adenosine (ATP).
Autacoids
Autacoids are formed locally and act on the function of other cells in their immediate environment. They are involved in inflammation and are classified as serotonin and histamine.
Histamine
Histamine is an amine stored in mast cells in the skin, gastric mucosa, lung lining, leukocytes and heart. Its function is as a mediator of allergic reactions and inflammatory diseases, and it is involved in the secretion of gastric juice. Histamine acts as a neurotransmitter in the CNS and regulates the sensation of pain and sleep.
Histamine is released by physiological processes (such as gastric juice secretion), pathological processes (inflammatory reactions, hypersensitivity), pharmacological stimulators (NMBs, opioids, NSAIDs, etc.) and physical agents (cold, heat).
- H1 receptors: their activation causes release of Ca2+ by increasing its intracellular concentration.
- H2 receptors: are linked to the activity of adenylyl cyclase and the production of cAMP.
Serotonin
Serotonin Receptor: G protein-coupled. 5-HT3: substances synthesized in serotonergic neurons that act as neurotransmitters. They exert great influence on the psychoneurological system, which is why they are called the neurons of mood.
Pharmacological actions
- Peripheral level: cardiovascular (vasoconstriction, cardiac stimulation), gastrointestinal (increased motility) and bronchi (bronchoconstriction).
- CNS: regulates digestive activity, sleep, appetite, temperature and pain control.
Drugs: sumatriptan, zolmitriptan, sibutramine, buspirone, fluoxetine (paroxetine), ondansetron, granisetron and tropisetron. All interfere with serotonin receptors. Sumatriptan: a 5-HT1D receptor agonist, used in the treatment of migraine attacks.