L72: Drugs Acting On Sympathetic NS Flashcards
Sympathomimetics vs Sympatholytics
Sympathomimetics: (mimic action of SNS)
Direct: activation of receptor (agonist)
Indirect: increase release, decrease breakdown of neurotransmitter
Sympatholytics: (reduce action of SNS)
Direct: block receptor activation (antagonist)
Indirect: inhibit NE synthesis, storage and release
***Adrenergic receptors
α1: Vasoconstriction, Smooth muscle contraction
α2: Decreased presynaptic NE release
β1: Increased HR, contractility
β2: Vasodilation, Smooth muscle relaxation
Adrenaline
Blood vessel more alpha1 but higher affinity for beta2 than alpha1
Beta1: ↑cardiac output
Beta2: low dose vasodilation
Alpha1: high dose vasoconstriction
—> overall small vasodilation —> small ↓ in peripheral resistance
Overall: ↑ HR, small ↓ in peripheral resistance, mild ↑ BP
Other smooth muscles: Beta2: ↑ relaxation
Use: anaphylactic shock, asthma
SE: hypertension, tachycardia
Noradrenaline
Beta1: ↑ cardiac output
Beta2: low affinity
Alpha1: vasoconstriction
—> overall significant vasoconstriction —> significant ↑ peripheral resistance —> reflex bradycardia —> not much change in cardiac output
Overall: reflex bradycardia, significant ↑ peripheral resistance, significant ↑ BP
Other smooth muscles: Beta2: low affinity: small relaxation
Use: hypotension
SE: hypertension, tachycardia
NE vs E
NA: ↑↑resistance, ↑↑BP, ↓HR
E: ↓resistance, ↑BP, ↑HR
Phenylephrine
Xylometazoline
Oxymetzoline
Selective Alpha1 agonists:
vasoconstriction —> ↑peripheral resistance —> ↑BP
Other smooth muscle: ↑contraction except GI which relax
Use: Decongestant
SE: Hypertension, reflex bradycardia
Clonidine
Selective Alpha2 agonist
Inhibition of presynaptic NE release —> ↓vasoconstriction —> ↓peripheral resistance —> ↓BP
Use: Hypertension, migraine
SE: Rebound hypertension, orthostatic hypotension, drowsiness, oedema
Isoproterenol (isoprenaline)
Non-selective Beta agonist
Increase CO + significant decrease peripheral resistance
—> small decrease blood pressure
Beta2 —> smooth muscle relaxation
Use: asthma (obsolete)
SE: tachycardia
Dobutamine
Selective beta1 agonist: increase CO —> increase BP (for shock and heart failure)
SE: Hypertension, tachycardia
Terbutaline
Salbutamol
Selective beta2 agonist
- Decrease in blood pressure
- Smooth muscle relaxation (for asthma)
Terbutaline: Prevent premature labour by relaxing uterine smooth muscle
SE: tremor, tachycardia (stimulating beta1)
Mirabegron
Selective beta3 agonist
Use: Overactive bladder
Tyramine
Rich in fermented cheese
Increased NE release through NET (avoid taking MAO inhibitor at the same time)
Amphetamine
increase NE release through NET
CNS stimulant (mood elevation, anorexiant, ADHD)
SE: insomnia, psychosis, tachycardia
Ephedrine
increase NE release through NET
also Alpha and Beta agonist
Nasal decongestant
***All drugs
Non-selective α/β agonist: Adrenaline, Noradrenaline
α1 agonist: phenylephrine, xylometazoline, oxymetazoline (nasal congestion)
α2 agonist: clonidine (hypertension)
α1 antagonist: prazosin, terazosin, doxazosin (hypertension), tamsulosin (BPH)
α2 antagonist: yohimbine (no use)
α1, α2 antagonist: phenoxybenzamine, phentolamine (phaechromocytoma)
β1 agonist: dobutamine (heart failure, shock)
β2 agonist: salbutamol, terbutaline (asthma)
β3 agonist: mirabegron (overactive bladder)
β1 antagonist: metoprolol, atenolol (angina, dysrhythmia, hypertension)
β2 antagonist: butaxamine (no use)
β1, β2 agonist: Isoprenaline (no use in asthma)
β1, β2 antagonist: propranolol (anxiety, tremor, angina, dysrhythmia, hypertension), timolol (glaucoma; contraction of ciliary muscle —> open canal of Schlemm)
α, β antagonist: labetalol, carvedilol (heart failure)
Increase NE release through NET: ephedrine (nasal congestion), tyramine, amphetamine (CNS stimulant)
Decrease NE release: reserpine (rarely used), methyldopa (Hypertension)
Inhibit NE release: guanethidine (no use)
