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Different drugs used to dilate airways, their mechanism of action and the clinical conditions which they are used to treat

List the three classes of bronchodilator drugs

- Beta-adrenoceptor agonists
- Anticholinergic drugs
- Phosphodiesterase inhibitors

List Beta adrenoceptor agonists

Beta 1 & Beta 2 non-selective:
- isoprenaline

Beta 2 selective:
- salbutamol, terbutaline

long acting Beta 2 agonists
- salmeterol, formoterol

List anticholinergenic drugs (prevent release of ACh)

- atropine
- ipratropium; tiotropium (long acting)

List phosphodiesterase inhibitors

- theophylline

Which class of bronchodilators do we use primarily for asthma?

Beta adrenoceptor agonists

Which class of bronchodilators do we use primarily for COPS?

As it is less reversible, we use all 3 categories
- B adrenoceptor agonists
- Anto-cholinergenics
- Theophylline

Two telltale signs of asthma and what are they treated with?

- bronchocontriction with bronchodilators
- inflammation with corticosteroids

What are the layers of the cross section of an air-way?

How would a cross section of a lumen look histologically when it has asthma?

- a little bit of mucus

- epithelium on airway
- basement membrane (blue) is thickened
- smooth muscle: much more than usual
- mucus sitting in the lumen
- oedema in the submucosa

Aim of Beta-2 adrenoceptor agonists?

To relax Airway Smooth Muscle (ASM) by binding to Beta-2 receptors on surface of ASM cells

How are beta 2 adrenoceptor agnists taken?

inhaled usually

Mechanism of Beta 2 agonists on the Beta 2 adrenoceptor intracellularly on the ASM

Beta 2 adrenoceptor agonists can also have these effects besides relaxing airway smooth muscle (minor)

- inhibit mast cell release (LT, histamine)
- increase mucociliary clearance (by increasing ciliary beat frequency)

Outline the sensitisation (1st degree exposure) process in asthma

APC to T helper (IL-4) --> b cell --> IgE --> binds to Mast cells.

Salbutamol vs salmeterol on how it enters/affects the cell

- salbutamol directly goes and affects beta adrenoceptor
- we think salmeterol hangs around lipid membrane and 'leeches' out to the beta receptor adjacent

Salbutamol vs salmeterol on length of duration

Salbutamol is known as a short acting beta agonist

Which nerve innervates the bronchial smooth muscle?

X (vagus)

How does anticholinergics work at the Smooth Muscle receptors?

- Ach is released from the vagus efferent nerve.
- Anticholinergics dinds to the Ach receptors on the smooth muscle.

Salmeterol (LABA) vs Ipratropium (Anticholingeric) over time for FEV1

Pathway of Ach pathway to cause constriction (diagram)

(i) = inactive , (a) = active form
- Note B2 receptors that activates cAMP pathway
- Phosphorylated Myosin and Actin causes contraction.

Diagram of how anticholinergenics work on the synapse on ASM

Tiotropium vs ipratropium

- 10x more potent
- long acting version of anticholinergenic
- half life of 34.7h, while ipratropium has 0.25h.
- tiotropium has a prolonged blockade of M3 receptors

Phosphodiesterase (PDE) inhibitors - most common?


Theophylline - how does it work on relaxing smooth muscle?

Increases cAMP

Downsides of PDE inhibitors?

- narrow therapeutic range (small difference between effective dose and dose causing side effects)
- side effects are nausea and vomiting

How do PDE inhibitors work intracellularly to relax muscle?

- cAMP is broken down by PDE to AMP.
- If we inhibit breakdown, we hav emore cAMP and hence more relaxation of muscle

List the isozymes of PDE in different tissues (airway, vascular, endothelium, neutrophil, T cell) (phosphodiesterase)

- theophylline is non selective

Distribution in smooth muscle
Airway: II, IV, V
Vascular: III, IV

Endothelium III, IV

Neutrophil : IV
T Cell: IV

IV is the most common.

What is a good isozyme of PDE to inhibit?


PDE4 inhibitors that are likely to be released in the market


Releationship of BA's on cAMP

cAMP is increased

which drug targets M3 receptors on smooth muscle? (anticholinergenic)


Asthma treatment: When should we take SABA's

- wheezing
- before exercise

Asthma treatment: When should we take ICS?

For all but the mildest of asthma

Asthma treatment: When should we take LABA's

We take it with ICS usually
- LABA + ICS for moderate to severe asthma


Chronic obstructive pulmonary disease (COPD

COPD vs Asthma (pathogenesis)

- Destruction of alveoli
- CD8+ cell (Th1)

- CD4+

How is lung function (FEV1) affected at COPD and Asthma?

Clinical differences (symptoms) of Asthma and COPD?

If bronchodilators don't work so well on people with COPD, how do we treat them?

- we still give them bronchodilators
> Beta adrenoceptor agonists
> Anticholinergics
> theophylline (if they are already taking it)
- Long acting agents
> Tiotropium (once/day)
> Salmeterol, Formoterol
- ICS for advanced disease
> No decline in lung function
> decrease in exacerbation rate

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