16 - Respiratory Pharmacology Flashcards
What is the pathophysiology behind asthma?
- TH2 and eosiniphil driven inflammation resulting in mucosal oedema, bronchoconstriction, mucus plugging and bronchial hyperresponsiveness
- Chronic inflammatory, intermittent, reversible
- Parasympathetic M3 causes bronchoconstriction
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What does asthma control mean?
- Minimal symptoms during day and night
- Minimal need for reliever medication
- No exacerbations
- No limitation of physical activity
- Normal lung function (FEV1 and/or PEF >80% predicted or best)
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What should you check with a patient before you step them up or down the asthma treatment ladder?
- Adherance
- Inhaler technique
- Eliminate trigger factors
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What is the stepwise approach for the treatment of asthma?
- Step 1 – short acting β2 agonists as needed, consider low dose ICS
- Step 2 – regular low dose ICS
- Step 3
A. LABA + low dose ICS
B. LABA + ↑ dose ICS / stop LABA if no effect
- Step 4 – LABA + high dose ICS (can add LTRA/aminophylline)
- Step 5 – daily oral steroid + high dose ICS + consider others
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Should you add LABA or LTRA after low dose ICS?
NICE suggests LTRA as this is cheaper but BTS/SIGN says LABA and most patients do end up on this
How do SABA’s act to help mild/intermittent asthma?
- Bronchodilation by agonising beta-2 receptors
- Gs protein so activate adenyl cyclase, and then PKA which phosphorylates myosin light chain kinase to inhibit smooth muscle contraction.
- Also increases mucus clearance by action of cilia
- Symptom relief by reversing bronchoconstriction, only use as required
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What are some examples of beta agonists and when are they used?
SABA: as needed
LABA: add on therapy with ICS and p.r.n SABA. Can be used as a preventer before exercise to prevent exacerbations and improve lung function
(formoterol has rapid onset of action similar to salbutamol but long acting. More potent and efficacious than salmeterol)
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What are some adverse affects that can occur when using B2 agonists and what drugs cannot be used alongside it?
- May generate a tolerance if constantly using
- Tachycardia
- Palpitations
- Anxiety
- Tremor
- Muscle cramps (LABA)
- Increased renin and glycogenolysis so could raise b.p
- Don’t use with beta blockers as may reduce effects of beta agonist
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What should LABA always be taken with and why is it taken as a combined inhaler?
ICS - increased risk of death when prescribed alone
- Adherance
- Ease of use
- Less prescriptions
- Safer
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When are inhaled corticosteroids added on to asthma treatment and what is their mechanism of action?
- When reliever alone not sufficient and using more than 3 times a week or waking up with symptoms
- Reduces mucosal inflammation, widens aiway and reduces mucus to reduce symptoms, exacerbations and death
- Lipid soluble so activate intracellular GC receptor alpha and cause gene activation of B2 receptors and inactivation of inflammatory mediators and cytokines
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What are some side effects of ICS being used as a regular preventer therapy?
- Can have local immunosuppressive action e.g oral candidiasis, hoarse voice
- Pneumonia risk with COPD
- Very few ADRs if taken correctly
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What are some examples of ICS’s and what are their pharmacokinetic properties?
- Poor oral bioavailability which is why little side effects and you inhale.
- Slow dissolution in aqueous bronchial fluid but high affinity for glucocorticoid receptor
- When inhaling some will go to stomach and some will sta in mouth
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After a an ICS and a LABA have been added to an asthma treatment and this is still not controlling the patient’s condition, what can be added next?
- Increase dose of ICS to medium by having two puffs a day
- Add LTRA (montelukast)
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What is the mechanism of action of leukotriene receptor antagonists like montelukast?
- Leukotrienes are released by mast cells/eosinophils, induce bronchoconstriction, mucus secretion and mucosal oedema and promote inflammatory cell recruitment through GPCR CysLT1
- LTRAs block the effect of cysteinyl leukotrienes in the airways at the CysLT1 receptor
- Only works in 15% of asthmatics
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What are the side effects of using a LTRA?
- No major drug interactions but:
- Headache
- GI disturbance
- Dry mouth
- Hyperactivity
- Angiooedema
- Anaphalyxis
- Fever
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