The lungs and drugs

The lungs and drugs

Bronchodilators that you will mostly come across are known as β2-adrenoceptor agonists. They act on the β2- adrenoceptors and therefore relax the smooth muscle, enhance the ciliary clearance of mucus and reduce the pro-inflammatory action of mast cells. They are usually given by inhalation but oral tablets and injection preparations are also available. For acute episodes, salbutamol and terbutaline are used because of their fast-acting nature and reasonable duration of approximately five hours. Salmeterol and formoterol are used as a dose rather than in acute situations as they take a little longer to act, but typically last much longer – approximately 8–12 hours. Other bronchodilators include xanthenes, such as theophylline or aminophylline (relaxation of smooth muscle but action is unclear), cysteinyl leukotrine receptor antagonists, such as montrelukast, and muscarinic receptor antagonists, such as tiotropium or ipratropium (increases acetylcholine expression and reduces mucus secretion).

Anti-inflammatory drugs, such as glucocorticoids, reduce the formation of pro-inflammatory cytokines and COX-2. Steroids also reduce the allergic response in asthmatics by inhibiting the specific cytokine that is responsible for regulating mast cells – the eventual result is fewer mast cells in the respiratory mucosa. They are given as a daily dose, commonly by inhalation – known as a ‘preventer’ (beclometasone, fluticasone, etc.). The full required response is only achieved after weeks of continuous use, hence the essential role of respiratory practitioners to ensure that the patient understands how their drugs are to be taken. In advanced cases, a tablet form is used (e.g. prednisolone) to help bring the symptoms under control. In acute exacerbations i.v. steroids are used for immediate antiinflammatory

action to help maintain a patent airway. It is important to note that side effects are rare but the patient should only ever take steroids as directed by their prescriber. Oral thrush may occur. All steroids have a detrimental effect on the immune system and therefore opportunistic viruses may take advantage.

Neurological medicine

Parkinson’s disease is associated with decreased dopamine in the substantia nigra and corpus striatum, and effects are typically tremor, muscle rigidity and hypokinesis (reduced voluntary movement). Levodopa is considered

first-line treatment but is, unfortunately, extensively metabolised into dopamine peripherally preventing it passing through the blood-brain barrier and thus (i) requires a very high dose to spare enough levodopa to become centrally active and (ii) results in peripheral side effects. These problems are overcome by combining levodopa with an agent called carbidopa or benserazide that helps prevent its peripheral conversion which reduces the equipotent dose of levodopa to be reduced tenfold. Levodopa is short-acting and so side effects revolve around rapid alteration of symptoms ranging from dyskinesis and hypokinesis to rigidity fairly rapidly. These effects

usually progress over time but more instant side effects include nausea and vomiting, and postural hypotension.

Other treatment options increasing in popularity include dopamine receptor agonists, such as pergolide, ropinerole and pramipexole.

Anxiolytic and hypnotic drugs are widely used to reduce anxiety, muscle tone, aggression, convulsions and to help sedate patients. Benzodiazepines such as diazepam, temazepam, nitrazepam, etc. act on γ-aminobutyric acid

(GABAA) receptors enhancing the effect of this inhibitory amino acid in the central nervous system. This relaxant effect helps to break the anxiety (for example dental procedures, flying, phobias, etc.) and sustained muscle contraction/ increased tone (e.g. cerebral palsy, acute back pain, etc.). They are typically well absorbed orally and peak plasma concentration occurs within the hour. Side effects include drowsiness and poor coordination, so the patient is advised not to drive.

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