Mucolytics Flashcards
Example of a mucolytic
Acetylcysteine, Carbocysteine
How do mucolytics work?
In therapeutic doses, paracetamol is metabolised mainly by conjugation with glucuronic acid and sulfate. A small amount is converted to N-acetyl-p-benzoquinone imine (NAPQI), which is hepatotoxic. Normally, this is quickly detoxified by conjugation with glutathione. However, in paracetamol poisoning, the body’s supply of glutathione is overwhelmed and NAPQI is left free to cause liver damage. Acetylcysteine works mainly by replenishing the body’s supply of glutathione. Acetylcysteine also has antioxidant effects, which may contribute to its effect in preventing contrast nephropathy, although this is not completely understood. If acetylcysteine is brought into contact with mucus, it causes it to liquefy. For patients who have tenacious respiratory secretions (e.g. in bronchiectasis), this may aid sputum clearance.
Indications for mucolytic
As the antidote for paracetamol poisoning.
To help prevent renal injury due to radiographic contrast material (contrast nephropathy).
To reduce the viscosity of respiratory secretions (acting as a mucolytic).
Contraindications of mucolytics
History of an anaphylactoid reaction to acetylcysteine does not contraindicate its use in future, if it is required. It is important that such reactions are not labelled as ‘allergic,’ which may lead to effective treatment for paracetamol poisoning being inappropriately denied. However, it is essential to obtain specialist advice if there is any doubt.
Side effects of mucolytics
When administered intravenously in large doses for paracetamol poisoning, acetylcysteine can cause an anaphylactoid reaction. This is similar to an anaphylactic reaction (presenting with nausea, tachycardia, rash and wheeze), but involves histamine release independent of IgE antibodies. Therefore, once the reaction has settled (by stopping the acetylcysteine and giving an antihistamine ± a bronchodilator), it is usually safe to restart acetylcysteine, but at a lower rate of infusion. When administered in nebulised form as a mucolytic, acetylcysteine may cause bronchospasm. Therefore, a bronchodilator (e.g. salbutamol) should usually be given immediately beforehand.
Interactions of mucolytics
No significant interactions
Patient information on mucolytics
Explain that you are offering treatment with a paracetamol antidote. It is given slowly through a drip over 21 hours. If it is started within about 8 hours of a single overdose, you can say that it is very effective and, provided it is administered correctly, should completely prevent serious damage to the liver. Emphasise the importance of avoiding interruptions to the treatment, while acknowledging the inconvenience of being ‘tied to a drip’ for the best part of a day. Mention that it occasionally causes a reaction involving a rash, nausea, or wheeziness. They should alert staff if they notice any of these symptoms, so that the infusion can be interrupted and treatment given.
Elimination of mucolytics
Renal
