Qu’est-ce qu’un Béta-Bloquant ?
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Qu’est-ce qu’un Béta-Bloquant ?

September 2, 2019


Betablockers are used in cardiology since
the middle of the sixties They are used in hypertension but not only they are also used in heart failure in arrhythmia and other cardiopathies like angina and heart stroke They are not limited to cardiovascular pathologies I will tell you about the others further in the video Let’s talk first about bêta adrenergic receptors physiology which are bêta blockers target this adrenergic receptor in blue is composed of 7 transmembrane patterns it is linked to
a G protein through which it stimulates the adenylate cyclase that transforms the ATP in AMPc so that it can transduce the signal The agonists or activators of the bêta adrenergic
receptors are for example the adrenaline the noradrenaline dopamine dobutamine and salbutamol
the bêta receptor is not these molecules principal target which explains their side effects The AMPc obtained after the ATP transformation
is a second messenger that will activate the PKA or kinase protein A this protein will
phosphorylate many different proteins which explains the diversity of the bêta blockers
effects and their multiple indications There is 3 types of bêta adrenergic receptors
The beta 1 receptors located in the heart and the kidney’s juxtaglomerular apparatus then the beta 2 receptors located in the blood vessels and the lungs there is also the Bêta
3 receptors which are located in the adipocytes and after their stimulation the lipolysis is
increased I will focus here on the bêta 1 and 2 receptors The bêta 1 stimulation results in a positif inotropic effects which means an increase
of the contraction’s strength but also a positif chronotrope effect which means the increase
of the heart frequency a positif dromotropic effect which means an increase of the atrioventricular
conduction speed and finally a positif bathmotropic effect which means an increase of the ventricular
excitability so in general this will lead to a heart stimulating effect and on top of
it there will be an increase of the renin secretion from the kidney’s juxtaglomerular
apparatus The bêta 2 receptor activation will lead
to a cardiac stimulation effect but this is effect is not predominant we will mostly find
an effect on the muscular fibres relaxation which are found in many organs the consequences
will be a vasorelaxation an intestinal relaxation a bronchorelaxation put to use in asthma with
the bêta 2 mimetics for example salbutamol and terbutaline
Then there is also a uterine relaxation put to use in the premature deliveries
Those are the obtained effects after the stimulation of these tree receptors with for exemple the
adrenaline the bêta blockers will block these receptor
and have opposite effects The bêta blockers are a major class very
used of great therapeutic interest in the vascular field they are catecholamine competitive
antagonists which are the adrenaline and noradrenaline Only the levorotatory isomer hold the bêta
blocker activity these molecules don’t block only the bêta receptors they can also block
the alpha receptors like the labetolol which is used for pregnant women because it’s less
powerful than the others the bêta blockers are ranked in two groups the cardioseletive
and the non-cardioselective among these two groups we can either find those with an ASI
and those without the ASI I will explain the ASI later
As for the selectivity the cardioselective bêtablockers are selective of the bêta 1
receptors which means that they only act and this type of adrenergic receptors this helps
avoid the side effects provoked by the bêta 2 receptors they help reduce the cardiac work
and heart oxygen consumption which translates in negative inotropic, chronotropic, dromotropic
and bathmotropic effects the heart effect is to reduce the cardiac output, the blood
pressure and reduce the peripheral resistance in the renal side they will reduce the renin
secretion which will lead to the inhibition of the renin angiotensin aldosterone system
In this system the live synthesizes the angiotensinogen which will be transformed in angiotensine
1 the renin will transforme this angiotensine in the angiotensine 2 which will leas to the
aldosterone secretion the aldosterone effects are the water-soluble retention the volemia
increase and then hypotension which will all be prevented by the betablockers
The non cardioselectiv will block the bêta 1 and 2 receptors so they are responsible
for many side effects because of this bêta 2 receptor blockage The side effects are for
exemple hypoglycemia by the way it increase hypoglycemia in diabetic patients and hides
the adrenergic signs of hypoglycemia like anxiety, sweating palpitations and trembling
other side effects can occur like vasoconstriction Raynaud’ syndrome a bronchoconstriction that’s
why there are forbidden for patients with asthma or BPCO but also an intraocular pressure
decrease put to use in the glaucoma treatment About the ASI mentioned earlier it is actually
an intrinsic sympathomimetic activity which means that the bêta blocker has a partiel
agonist activity this allows to limit the bradycardic effect and the risks of Raynaud’s
syndrome aggravation Atenolol is cardioselective we can see it
on the molecule with the benzene cycle in para and found in all the cardioselectives
Oxprenolol has an ASI activity and we can see it with the benzene cycle in ortho Acebutolol
is cardioselective and has an ASI activity at the same time we can see on the molecule
that the benzene cycle is ortho and para I am going to share with my mnemonic means to
remember the cardioselective bêta blockers remember the phrase : New Exclusive Bêta
Blockers Act in Majority As Cardioselective each words majuscule represents a bêta blocker
as you can see with Acebutolol Celiprolol For those with an ASI the phrase to remember
is Contains Partial Agonist Like Properties and again each majuscule represents a bêta
blocker As for the pharmacokinetics the bêta blockers
are divided into two groupe the lipophilic bêta blockers and the hydrophilic bêta blockers
the lipophilic have a good digestive absorption a strong tissue distribution so they can pass
through the blood-brain barrier and the fetal-placenta barrier which leads to neurologic effects
and a fetal toxicity They have a small half-life time so they need to be taken 2 to 3 times
a day their hepatic first pass effect is important so they have a strong interindividual variability
The urinary elimination is in form of an inactive metabolite so we have to adapt the posology
for patients with kidney failure An example of lipophilic bêta blockers are propranolol
and metoprolol On the other hand hydrophilic bêta blockers
have a small digestive absorption a small tissue distribution so less side effects their
half-life time is longer so they can be taken one time a day they are little metabolized
so there is less interindividual variability also they have an unchanged renal elimination
for example we have sotalol and labetolol the lipophilic disadvantage is that they can
lead to many side effects like nightmares insomnia to avoid them we have to take the
betablockers in the morning but also hallucinations and fatigue If the patient doesn’t tolerate
them and has these side effects we can tell him to switch to the hydrophilic
bêta blockers As I said in the beginning bêta blockers
are used in many illnesses like hypertension where they act as anti-hypertensive they are
also used in heart failure, angina, and also in arrhythmia Bêta blockers are part of the
second class except sotalol that is part of the third class with amiodarone In migraine propranolol is used as a background treatment they are also used in glaucoma where timolol
allows to reduce the intraocular pressure we can also find them in the treatments of
essentials trembling and hyperthyroid in Asthma we use the beta 2 mimetic in other terms bêta 2 adrenergic receptor agonists which are the opposite of bêta blockers that are forbidden in asthma and BPCO Thank you for watching I hope you enjoyed
the video so you can like the video and don’t hesitate to subscribe 😉

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  1. Je suis asthmatique, mais je n’ai plus fait de crise depuis plus de 15 ans (Grace notamment au sport). Mon médecin m’a prescrit le Geltim pour traiter mon glaucome débutant. Y’a t’il un risque respiratoire particulier car ce médicament contiendrait des bêta bloquant (j’ai la frousse après avoir lu les effets indésirables et vu cette vidéo).

  2. Super vidéo je partage aux potes de promotion. On a maintenant une chance de réussir notre partiel de pharmaco, merci.

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