Drugs used for Coughing
Coughing is a reflex response. Receptors (stretch receptors) are stimulated by irritants in the bronchial mucosa. They signal along vagal afferents which activate the cough centre within the medulla.
Opioids – Codeine, hydrocodone
These are u-opioid agonists that act centrally to reduce the sensitivity of the coughing centre.
They are used as anticough medication and work at lower doses than that needed for pain relief.
Benzonatate
This has local anaesthetic action which blocks voltage gated sodium channels.
It reduces the responsiveness of airway stretch receptors, stopping desire to cough after a deep breath.
Diphenhydramine
This is a first generation H1-receptor antagonist normally used for nausea and vomiting
But it also acts centrally in order to decrease the sensitivity of the coughing centre.
Mucolytics – Carbocysteine, N-acetylcysteine
These decrease the viscosity of mucus in the lungs by breaking disulphide bonds within glycoproteins
They are used to treat mucus plugs in cystic fibrosis and exacerbations of COPD
NAC is also used as an antidote for paracetamol toxicity as it regenerates reduced glutathione, which helps to metabolise the toxic product NAPQI from paracetamol breakdown.
Drugs countering smoking
These drugs are very useful in helping people quit smoking, as they target the effects of withdrawal.
Varenicline
This is a nicotine receptor partial agonist which reduces cravings and withdrawal.
It is started 1 week before patient intends to quit and is used for around 12 weeks.
Varenicline is not available in some countries because of the levels of nitrosamines in some batches of the medication.
Side effects
Nausea is most commonly felt and sleep disturbances.
Contraindications
Pregnancy and breast feeding.
Links to suicide have been disproven however it is still recommended to stop if increased suicidal thoughts occur.
Bupropion
The mechanism of action is not fully understood, but it is thought to act as a noradrenaline/dopamine reuptake inhibitor, as well as a nicotine antagonist.
It is commenced 1 to 2 weeks before the patient intends to quit.
Side effects
Small risk of seizures, weight loss
Contraindications
Pregnancy
Breastfeeding
Epilepsy
Nicotine replacement therapy
These are available over the counter and directly replace nicotine.
They are available in the form of tablets, gums and patches.
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