Drugs affecting the respiratory system Flashcards
Overview of the respiratory system
- Nasal cavity warms, humidifies and cleans inspired air thereby protecting surface from dehydration, temp changes and pathogens
- Diaphragm expands pleural cavity and sucks air from external environment towards gas exchange surfaces
- Bronchial tree transmits air to bronchioles= main area of resistance to airflow
- Alveoli= large s.a.
- Vascular supply matches perfusion to ventilation and epithelium major site of ACE
What is asthma?
- Paroxysmal, reversible airway obstruction (bronchoconstriction)
- Caused by airway inflammation and bronchial hyperactivity
- With variability in symptoms and lung function
What are the symptoms of asthma?
- Breathlessness (chest tightness)
- Wheeze
- Cough
- Diurnal variability (worse in the morning or at night)
What are the provoking factors of asthma?
- Exercise/ hyperventilation
- Food, additives
- Drugs (NSAIDs, beta-blockers)
- Cigarette smoke
Describe asthma rescue treatment
-Hypoxia (poor gas exchange):
=Oxygen
-Bronchoconstriction:
=Beta 2 agonists (salbutamol)= bronchodilator rapidly reduce airway obstruction, not 100% specific so risk activating beta 1 receptors in heart/ beta 2 receptors in muscle so inhaled medication reduces systemic effects
-Airways inflammation:
=Corticosteroids (prednisolone orally, hydrocortisone IV)= used to stabile severe attacks, few hors for apparent effects
What is COPD?
- Inflammatory response of lung to prolonged exposure to noxious particles (cigarette smoke, cannabis, dust exposure)
- Reversible and non-reversible airflow limitation (poor ventilation)
- Damage to small airways and alveolar spaces (poor gas exchange)
- Excess mucus production
- Recurrent infection
What are the non-pulmonary complications of COPD?
- Right heart failure (cor pulmonale)
- Peripheral oedema
- Weight loss
- Muscle wasting
- Osteoporosis
How do patients with COPD present?
- Chronic bronchitis= cough producing sputum most days for 3 months over 2 consecutive years
- Emphysema= enlarged air spaced distal to terminal bronchioles
- Bronchiolitis= fibrosis and inflammation of small airways
What are COPD risk factors?
- Smoking
- Occupation
- Recurrent infections
What are the signs of COPD?
- Resting RR> 20 breaths/min
- Accessory muscles
- Pursed lipped breathing
How is COPD managed?
-Lifestyle changes =Smoking cessation =Exercise based pulmonary rehabilitation -Pharmacological =Oxygen =Bronchodilators (beta 2 agonists, antimuscarinic, theophylline) =Corticosteroids (prednisolone) -Antibiotics -Surgical =Bullectomy, transplant
What are the NICE COPD guidelines?
-Mild (FEV1 50-80%) =Inhaled anticholinergic/ beta 2 agonist -Moderate =Regular anticholinergic/ LABA (long acting beta agonist) plus inhaled corticosteroids -Severe (FEV1<30%) =Regular anticholinergic plus LABA plus inhaled steroid =Oral corticosteroids (trial) -PaO2 < 7.3 kPa =Consider home O2
What are the drugs used to treat asthma and COPD?
- Beta 2 agonists (salbutamol)
- Anti-muscarinic drugs (ipratropium bromide)
- Xanthines (theophylline)
- Mast cell stabilising drugs (cromoglicate)
- Leukotriene antagonists (Montelukast)
- Corticosteroids (prednisolone)
Describe beta-adrenoceptors
- Sympathetic NS (T4 to T7)
- Beta 1= adrenoceptors. Heart= increased force and rate of contraction
- Beta 2. Lung= relaxation of smooth muscle surrounding bronchi and bronchioles, increased diameter, reduces air flow resistance and improves ventilation of alveoli, increases effectiveness of O2 and CO2 exchange. Blood vessels= vasodilation
- Beta-adrenoceptor antagonists used in heart disease may precipitate bronchospasm and are contra-indicated in asthma and COPD
What are the Beta 2 agonist effects?
-Smooth muscle in uterus, bladder, GI, airways (relaxation)
=Activation of beta 2 G-protein couple receptors
=Activates adenylyl cyclase resulting in generation of cAMP
-Vasculature (vasodilation of arteries and veins)
=Relax vessel wall smooth muscle
-Mast cells (anti-inflammatory)
=Inhibits release of inflammatory mediators (histamine, PGD2)
-Skeletal muscle
=Tremor
-Cell membranes
=Increased uptake of potassium
Short-acting= salbutamol
Long-acting= salmeterol
Describe Salbutamol
- Similar drugs= terbutaline, salmeterol
- Beta 2 adrenoceptor agonist (increase cyclic AMP), smooth muscle relaxation and bronchodilation
- Low dose inhaled: as required or prophylactic, high dose nebulised: asthma/COPD exacerbations, other uses: hyperkalaemia
- Tremor, tachycardia and palpitations, hypokalaemia
How are anticholinergics used in asthma/ COPD?
-Cholinergic receptors (M1,2,3) located in airways
=Acetylcholine is the neurotransmitter released from postganglionic neurones in the vagus nerve ending
-Cholinergic (muscarinic) agonists cause:
=Smooth muscle to contract so airway narrowing
=Submucosal glands to secrete mucus
-Cholinergic antagonists (anticholinergics) cause:
=Bronchodilation
=Reduced mucus production
Short-acting= ipratropium bromide
Long-acting= tiotropium
What are the adverse effects of anticholinergic drugs?
-Reduced secretions from other glands =dry mouth =scratchy throat -Reduced smooth muscle contraction =constipation =urinary retention -Reduced cholinergic effect (vagal tone) on heart =tachycardia -Headaches
Describe Ipratropium Bromide
- Similar: tiotropium (long-acting)
- Anticholinergic (anti-muscarinic), decreased mucus secretion, bronchodilation
- COPD, bronchial asthma, rhinitis
- Inhalation= tiotropium 20-40 micrograms 3-4x/day, nebulised= ipratropium 100-500 micrograms up to 4x/day
- Dry mouth, nausea, headache
Describe the Theophylline group
- Similar: aminophylline (used IV)
- Phosphodiesterase inhibitor- increased cAMP- PKA activation, TNFa inhibition and inhibition of leukotriene synthesis, bronchodilation
- COPD, asthma (now rarely)
- Twice daily slow release tablets, plasma level of 10-20 mg/L
- Tachycardia, palpitations, nausea
- Monitoring plasma concentration is useful (digoxin, phenytoin, gentamicin)
What are corticosteroids?
Anti-inflammatory
-Inhibit inflammatory cell recruitment
-Reduce oedema by reducing permeability of vascular endothelium
-Increase anti-inflammatory mediator production (IL-1 receptor antagonist, IL-10)
-Inhibits NF-kB and AP-1 synthesis which are required for pro-inflammatory mediator production
Brown/purple inhalers
What are the adverse effects of corticosteroids?
-Hyperglycaemia (careful in diabetes)
-Osteoporosis (reduced bone density)
-Proximal myopathy
-Skin thinning
-Suppression of pituitary adrenal axis
-Altered body fat distribution
-Hypertension
-Weight gain
-Growth suppression in children
-Infection susceptibility (esp. viruses, fungi)
Inhaled: beclomethasone
Oral: prednisolone
IV: hydrocortisone
Describe Prednisolone
- Similar: hydrocortisone
- Action at nuclear receptors, immunosuppression, anti-inflammatory
- Asthma, COPD exacerbations, RA, IBD
- 40mg daily for several days after exacerbations, intra-articular injections may help settle a flare
- Growth suppression, osteoporosis, weight gain, infections, skin changes, hyperglycaemia
What are leukotrienes?
-Synthesised from arachidonic acid
-Production increased in allergic responses and inflammation
-Airway effects:
=Narrowing
=Increased mucus production