Dextromethorphan HCl

A synthetic morphine derived from levorphanol . Dextromethorphan HBr salt is also in use.


Action:
They have the same anti-tussive activity as other morphine derivatives. And it is almost similar in depressing the cough as codeine.

Therapeutic Uses:
It is used for cough in minor throat and bronchial irritation such as that in common cold. It is most effective in reducing chronic non-productive cough.

Administration and dosage:
It is administered orally and its lozenges are also used for adults. The usual dosage of Dextromethorphan HBr is 10-20 mg every 4 hours for adults and children above 6 years.

Pharmacokinetics:
1. It is absorbed rapidly from GI tract.
2. Its onset of action is 12-30 minutes.
3. Its duration of action is 2-6 hours.

Adverse Effects:
Very rare but nausea and GI tract disturbances may occur sometimes.

Benzonatate

It is a local anesthetic anti-tussive drug.


Mechanism of Action:
It acts as cough depressant in two ways:
1. It anesthetizes the stretch receptors of vagal afferent fibers in bronchi, alveoli and pleura that are involved in cough reflex.
2. It depresses the cough reflex at the level of medulla at the point where afferent impulse is transmitted to the motor nerves.

Therapeutic Uses:
1. Cough:
It is used for the symptomatic treatment of cough. It can be effective in reducing cough in conditions like pneumonia, common cold, bronchial asthma and tuberculosis.

2. As local anesthetic:
It is used in liquid filled capsules (Which are chewed), as local anesthetic of oropharyngeal cavity for attentive intubation.

Administration and dosage:
It is given orally. And its dose for adults and children older than 10 years of age is 100 to 200 mg 3 times daily.

Pharmacokinetics:
1. Its onset of action is 15-25 minutes.
2. Its duration of action is 2.5-8 hours.
3. Anesthesia of oropharyngeal cavity occurs within 1 minute.

Adevrse Effects:
Sedation, Headache, Nausea, Pruritis and skin eruptions, Hypersensitivity and nasal congestion.

Hydrocodone

(Similar to Codeine)

Hydrocodone are used as Hydrocodone bitartrate.

They are more sedative than codeine at equal therapeutic doses.

Elimination half life is 3.8 hours.

Codeine (Sulphate or phosphate)

It is phenanthrene derivative-opiate agonist.

Mechanism of Action:
It lowers the cough reflex by direct effect on the cough center in medulla of the brain that appears to exert a drying effect on respiratory tract mucosa and increased viscosity of bronchial secretions.

Action:
It has less effect on cough than morphine if we consider treatment on weight basis.

Therapeutic uses:
1. Cough:
It can be used for the (symptomatic) treatment of non-productive cough.

2. Analgesic

Administration and dosage:
It is administered orally for anti-tussive effect. Its dosage is 10-20 mg every 4-6 hours for adults and children above 12 years age. The dosage is half for children between 6-12 years.

Pharmacokinetics:
1. It is well absorbed from G.I. Tract.
2. Peak anti-tussive effect occurs after 0.5 to 2 hours and remains for (may) up to 4-6 hours.
3. It can be distributed into milk.
4. It is metabolized in the liver and excreted in the urine.

Adverse effects:
Its side effect is rare, which may show nausea, vomiting, constipation with repeated doses, dizziness and sedation.

Classification of Drugs used to treat cough

1. Anti-tussives
Codeine, Hydrocodone, Hydromorphone, Benzonate, Dextromethorphan HCl, Carbetapentane

2. Expectorant:
Guaifenesin, Guaiacol, Terpene hydrate, Creosate

3. Mucolytic agents:
Acetylcysteine, Bromohexine, Proteolytic enzymes such as trypsin, Ambroxol

Cough

It is the process of releasing air through the windpipe and mouth in a sudden noisy manner. Cough is initiated when there is a mechanical or chemical irritation to bronchi and trachea or by pressure from adjacent structures. Larynx and carina are especially sensitive to chemical stimuli such as SO₂ gas or chlorine gas.

Useful aspects of cough:
It is a physiological mechanism which:
1. Clears the respiratory pathways from foreign materials and extra secretions
2. May help to prevent sudden collapse of lungs.

Capreomycin

It is obtained from Streptomyces capreolus. It is peptide protein synthesis.


Its 1 gm IM injection leads to 10μg/ml of blood level.

It is used for the treatment of tuberculosis.
It may cause nephrotoxicity, ototoxicity, tinnitus and deafness.