Introduction of Antitussives
Antitussives are drugs that suppress or relieve coughing. They act centrally on the cough center in the medulla oblongata of the brain or peripherally on the cough receptors in the respiratory tract.
Classification of Antitussives:
a. Opioid Antitussives:
- Codeine: A mild opioid analgesic also used as a cough suppressant.
- Hydrocodone: A stronger opioid used for pain and as an antitussive.
- Dextromethorphan (DM): A non-opioid derivative with antitussive action.
b. Non-opioid Antitussives:
- Benzonatate: Acts by numbing the stretch receptors in the lungs and airways.
- Diphenhydramine: An antihistamine with antitussive properties.
Mechanism of Action:
Antitussives act by suppressing the cough reflex. Opioid antitussives act centrally on the brain’s cough center, while non-opioid antitussives like benzonatate act peripherally by numbing the stretch receptors.
Here’s an illustration of the mechanism of action of antitussives:
In the diagram:
- The Cough Reflex is initiated by Stretch Receptors in the Lungs & Airways.
- Opioid Antitussives act centrally to suppress the Brain’s Cough Center.
- Non-opioid Antitussives act peripherally to numb the Stretch Receptors, thereby reducing the cough reflex.
In the diagram:
- Antitussives act on the Central Nervous System (CNS).
- Within the CNS, they target the Opioid Receptors.
- This leads to the Suppression of the Cough Reflex.
- Antitussives also act on the Respiratory Tract.
- Within the respiratory tract, they target Cough Receptors.
- This action helps to Prevent the Initiation of the Cough Reflex.
Pharmacokinetics:
a. Codeine:
- Absorption: Well absorbed orally.
- Distribution: Widely distributed in the body.
- Metabolism: Metabolized in the liver.
- Excretion: Excreted in urine.
b. Dextromethorphan:
- Absorption: Rapidly absorbed from the gastrointestinal tract.
- Distribution: Crosses the blood-brain barrier.
- Metabolism: Metabolized in the liver.
- Excretion: Excreted in urine.
c. Benzonatate:
- Absorption: Rapidly absorbed.
- Distribution: Concentrated in the respiratory tract.
- Metabolism: Minimal metabolism.
- Excretion: Excreted in urine.
Pharmacological Actions:
a. Central Nervous System: Suppression of the cough reflex.
b. Respiratory System: Reduced coughing and potential for respiratory depression with opioids.
Therapeutic Uses:
These drugs are mainly used for the suppression of non productive/dry cough.
a. Codeine:
- Cough suppression
- Mild to moderate pain relief
b. Dextromethorphan:
- Cough suppression
c. Benzonatate:
- Cough suppression
Side Effects:
a. Codeine:
- Drowsiness
- Constipation
- Respiratory depression (in high doses)
b. Dextromethorphan:
c. Benzonatate:
- Drowsiness
- Upset stomach
- Allergic reactions
Contraindications:
a. Codeine:
- Asthma: Can exacerbate respiratory depression.
- Children under 12: Risk of severe respiratory depression.
- Pregnancy: Potential for neonatal opioid withdrawal syndrome.
b. Dextromethorphan:
- Concurrent use of MAO inhibitors: Risk of serotonin syndrome.
- History of substance abuse
c. Benzonatate:
- Children under 10 years: Risk of severe adverse reactions.
- Allergic reactions to ester-type anesthetics
Drug Interactions:
a. Codeine:
- Alcohol: Additive CNS depressant effects.
- Other opioids: Increased risk of respiratory depression.
b. Dextromethorphan:
- SSRIs: Risk of serotonin syndrome.
- MAO inhibitors: Risk of serotonin syndrome.
c. Benzonatate:
- Alcohol: Additive CNS depressant effects.
I hope this provides a comprehensive understanding of antitussives. Please comment if you have any further questions or need more details on any specific section.
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