ROLE OF Β BLOCKERS AND ANTI PLATELETS IN MI
ROLE OF Β BLOCKERS AND ANTI PLATELETS IN MI
WHAT IS MYOCARDIAL INFARCTION??
MYOCARDIAL INFARCTION commonly referred to as HEART ATTACK ,is death of cardiac muscle due to prolonged ischaemia
TYPES NSTEMI STEMI
β-BLOCKERS IN MI
CARDIOSELECTIVE β1 BLOCKERS Metoprolol Atenolol Acebutolol Esmolol Bisoprolol
NON SELECTIVE β1&β2 BLOCKERS Without intrinsic sympathomimetic
activity Propranolol Sotalol
MECHANISM OF ACTION OF β-BLOCKERS
β-Blockers Block cardiac β1 receptors
Decreases FOC ,HR ,BP
decrease myocardial oxygen demand
NEGATIVE CHRONOTROPIC EFFECT
NEGATIVE INOTROPIC EFFECT
METOPROLOL It is a cardioselective β1 blocker.(prototype) PK - it is well absorbed orally low bioavailabilty due to significant first pass metabolism.It is hydroxylated by CYP2D6 before excretion.Plasma t1/2 3-6 hrsDOSAGE-IV dose of 5mg over 2 min repeated every
5 min(total 3 doses) followed by 50 -100mg orally every 12 hrs.
PROPRANOLOL It is a non selective β blocker Well absorbed orally but low oral
bioavailability due to high first pass metabolism.
Lipid soluble Bioavailability is increased with food Its metabolites are excreted in urine mostly
as glucuronides.
contd. Plasma t½ is 3-5hrs More than 90% of propranolol is
protein bound DOSAGE- IV dose of 0.1mg per kg
divided into 3 doses at 5-10 min followed by 20-40mg orally every 6-8hrs
ATENOLOL Selective β1 blocker PK-incompletely absorbed orally but first
pass metabolism is not significant. Low lipid solubility Because of longer duration of action once
daily dose is sufficient. DOSAGE-IV dose of 5-10mg followed by
100mg orally once daily
BENEFITS OF β BLOCKERS High risk pts those who had large
infarcts should be put on β blockers for at least 2 yrs.
1 .SECONDARY PROPHYLAXIS OF MI prevents re-infarction prevents sudden ventricular
fibrillation at subsequent attack of MI
2.MYOCARDIAL SALVAGE DURING EVALUATION OF MI
Limit infarct size by reducing O2 consumption.
Prevent arrhythmias including ventricular fibrillation.
ADVERSE EFFECTS OF β BLOCKERS PROPRANOLOL Worsens peripheral vascular
diseases. GI upset Lack of drive Sleep disturbances Impotence in male pts Dry eyes and hair loss Sudden stoppage of propranolol
worsens the condition.
METOPROLOL Side effects are milder compared to
propranolol so it is most commonly used.
CONTRAINDICATIONS of non selective β blockers
Bronchial asthma DM Heart rate less than 60 /min systolic blood pressure less than 100 mmHg
β-blockers preferred in bronchial asthma and DM
Metoprolol Atenolol
ROLE OF ANTI PLATELETS IN MI• Drugs - Aspirin Dipyridamole P2Y 12 Receptors blockers Ticlopidine Clopidogrel
Prasugrel GP ןןb/ןןןa Antagonists Abciximab Eptifibatide Tirofiban
Mechanism of Antiplatelets
ASPIRIN It inhibits COX 1 and TX synthase
irreversibly. so thromboxane A2 formation is inhibited at low doses.
Inhibition of COX1 by aspirin in vessel wall decreases PGI2 formation at high doses
DOSAGE - Low dose 75 -150 mg per day or 300mg twice weekly
High dose greater than 900mg /day
CLOPIDOGREL Newer and more potent irreversible inhibitor
of platelets(P2Y12 receptor blocker) It is a slow acting drug activated in liver by
CYP2C19 . Omeprazole,an inhibitor of CYP2C19
reduces metabolic activation of clopidogrel Action lasts for 5 -7 days and t1/2 is 8hrs. Adverse effects are
bleeding,neutropenia,thrombocytopenia,epigastric pain
DOSAGE- 75mg OD
PRASUGREL Latest most potent and fast acting
P2Y12 receptor blocker. It is rapidly absorbed, completely
activated resulting in faster and more consistent platelet inhibition.
Activated by CYP2C19 but omeprazole interference is not prominent.
S/E –bleeding
CONTRAINDICATIONS- pts of ischaemic stroke and transient ischaemic attacks due to risk of intracranial hemorrhage.
DOSAGE-10mg OD For elderly and for
those less than 60 kg bodyweight 5mg OD is given.
loading dose of 60 mg is given for immediate action.
ABCIXIMAB(Gpııb/ıııa Antagonist)
It is Fab fragment of a chimeric monoclonal antibody against GPןןb/ןןןa protein.
Platelet inhibition occurs for 12 -24 hrs. It is non antigenic. T1/2 is 10 -30 min. It is expensive
S/Es – Haemorrhage Thrombocytopenia constipation
arrhythmias DOSAGE-0.25 mg per kg IV 10 -60
min before PCI followed by 10µg/min for 12 hrs.
COMBINATION THERAPY NSTEMI- aspirin + clopidogrel for 1 yr. STEMI –prasugrel+aspirin for pts
undergoing PCI Prasugrel is preferred over clopidogrel
in diabetes Aspirin + GPןןb/ןןןa antagonists for high risk pts
undergoing PCI Abciximab /eptifibatide/tirofiban infused
IV along with oral aspirin and s.c heparin reduce incidence of restenosis and subsequent MI after
coronary angioplasty
contd. GPןןb/ןןןa antagonists are infused for a maximum
of 72 hrs .• Aspirin and/or clopidogrel given to ACS pts treated
with thrombolysis.• Aspirin +GPןןb/ןןןa antagonists /prasugrel for
coronary Artery bypass surgery• Patency of recanalised coronary artery or
implanted vessel is improved and incidence of re occlusion is reduced by continuing aspirin+clopidogrel/prasugrel
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