SNS agonists Flashcards
Recall the type of adrenoceptor present in the heart, blood vessels and lungs respectively
beta 1, alpha 1, beta 2
What aspects of anaphylaxis are combatted by AD treatment?
Bronchoconstriction, bradycardia, vasodilation
Recall 5 clinical uses of adrenaline
Anaphylaxis Asthma Acute bronchospasm Anaesthesia Cardiogenic shock
How does AD combat cardiogenic shock?
Targets beta 1 receptor to help heart pump blood
Why is AD used in anaesthesia?
Maintains BP and prolongs bronchoconstriction in spinal anaesthesia via alpha 1 targetting
Recall 5 possible side effects of AD use
- Tachycardia can exacerbate arrythmias
- Thickened secretions
- SKeletal muscle tremor
- Cold extremities
- Hypertension
Recall 5 selective adrenoceptor agonists and their selectivities
Isoprenaline - beta Clonidine - alpha 2 Phenylephrine - alpha 1 Dobutamine - beta 2 Salbutamol - beta 2
Recall the pathophysiology of cardiogenic shock
LV dysfuntion –> decreased CO –> lack of tissue perfusion –> shock
Describe the duration of action of phenylephrine
Long-lasting because resistant to COMT breakdown
What drug (and it’s class) should be used as a nasal de-contestant and why?
Phenylephrine (alpha agonist) - reduces blood vessel dilation in nose
What is a midriatic?
Something that dilated the pupil
Which class of drugs make good midriatics?
Alpha agonists
What is clonidine’s main clinical use?
Glaucoma treatment
How does clonidine treat glaucoma?
Stimulates alpha 1 on blood vessels to reduce blood supply to ciliary body
What 2 receptors are present on the ciliary body and what are their roles?
Beta 1: humour production
Alpha 2: decreases beta 1 response
Recall 3 uses of clonidine
Glaucoma, hypertension, migraine
How does clonidine treat hypertension?
Agonises alpha 2 receptors to reduce SNS tone in vasculature
How does clonidine act to treat migraine?
Agonises alpha 2 to reduce beta-2 stimulated dilation of blood vessels
Describe the duration of action of isoprenaline
Long-lasting because resistant to MAO uptake
Recall 3 uses of isoprenaline
Cardiogenic shock, acute heart failure, MI
Why does isoprenaline have a risk of exacerbating arrythmia?
If you stimulate beta 2 –> venous BP falls –> increased baroreceptor firing
Which drug has been superceded by dobutamine?
Isoprenaline
Why is dobutamine a better drug than isoprenaline generally?
Less likely to cause reflex tachycardia as is more selective for beta 1 than beta 2
Describe the duration of action of dobutamine
Very short half life as highly susceptible to COMT breakdown
What is the mechanism of action of salbutamol in asthma treatment?
Reduces ability of SMCs to contract:
- Decreases PI hydrolysis –> less calcium released from stores
- Increases Na+/Ca2+ exchange
- Opens K+ channels so cell much more likely to be hyperpolarised
What does PI hydrolysis do normally?
Stimulates Ca++ release from intracellular stores to initiate SMC contraction
Why is salbutamol used in labour?
Reduces ability of uterine muscle to contract
Recall 2 uses of phenylephrine
- Nasal decongestant
2. Mydriatic
Why is isoprenaline useful in cardiogenic shick?
Activates beta 2 –> Reduces BP –> increased heart stimulation
