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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