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8/3/2019 Biochemistry of Emergency Drugs
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Biochemistry
of EmergencyDrugsMiss Yah Nee LoLecturer
Friday, August 26, 2011
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Learning Objectives
•Know the common classes of drugs used in the A&E especially
in Brunei•Be able to describe themechanism of action of
important classes of emergencydrugs
•The basic dosage and infusion
guide of emergency drugs?Friday, August 26, 2011
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Accident & Emergencysituations
• List down the common situations or conditions thatcomes into our own A&E department in the RIPASthat you can think of?
• Shortness of breath
• Anaphylactic shock• Cardiovascular problem e.g. heart block,
arrhythymia, etc
• Heart Attack
…
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Asthmatic/
COPD
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1. Aminophylline
• Bronchodilator
• Compound of the bronchodilatortheophylline with ethylenediaminein 2:1 ratio
• Ethylenediamine improves solubility• Theophylline relaxes bronchialsmooth muscles.
• MOA unclearFriday, August 26, 2011
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Aminophylline
• contradictions: hypersensitive, avoid bolus dose if patient taking Oral Theophylline
• Adverse Drug Ef ects: Nausea, Vomiting, abdominalpain, diarrhoea, headache, insomnia, dizziness...
• the potentially fatal: Convulsions, cardiacarrthymias, hypotension and sudden death after toorapid IV injecion
•Loading dose: 250 mg (Slow I/V in
15 mins)•Infusion Rate: 20-80 mils/hr
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2. Salbutamol
•Short acting B2-adrenergicreceptor agonist used for relief of bronchospasm
• racemic mixture with a 1:1 ratioof the isomer, levelbuterol ands-albuterol.
•The tertiary butyl group insulbutamol makes it moreselective for B2-receptors.
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3. Magnesium Sulphate
• sterile solution of magnesium sulphateheptahydrate in water for injection
• Electrolyte, anticonvulsants•
Indications:• Seizures of eclampsia• TDP• Hypomagnesaemia• Refractory VF
• Use with caution in renal failure• CNS depressant ef ects may be enhanced
in presence of other CNS depressant
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Adrenaline
• Sympathomimetic• hormone and a neurotransmitter
• increases heart rate, constricts blood
vessels, prepare us for ‘fight-or-flight’response of the sympathetic nervoussystem.
• Chemically it is a catecholamine, a
monoamine produced only by theadrenal glands from the a.a.phenylalanine and tyrosine
•
used best for anaphylactic shock
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Doxapram (Dopram)
• Doxapram hydrochloride
• Central Respiratory stimulant
• Stimulates increase in tidal volume and
RR• Stimulates the chemoreceptors in the
carotid arteries which in turn stimulatesthe respiratory centre in the brain
• Thought to stimulate the carotid body byinhibiting certain potassium channels
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Bradycardia
& Heart
BlockFriday, August 26, 2011
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1. Atropine•
MOA: Anticholinergic agent thatcompetitively blocks the muscarinicreceptors
• Muscarinic receptors found in peripheral
tissues such as the heart, intestines,bronchial muscles, iris and secretory glands.
• abolishes bradycardia and reduces heartblock due to vagal activity
•
Adverse reaction: Dry mouth, Dysphagia,contipation, restlessness, confusion, etc
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2. Isoprenaline
• MOA: a beta-1 and beta-2 adrenergic receptoragonist.
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Antiarrythmics
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Classes of antiarrythmics
• Class 1- Membrane stabilizers
• Class Ia- lengthen action potential, prolongrepolarization, prolong PR, QRS, QT. e.g.Quinidine, procainamide,disopryamide
• Class 1b- shorten action potential, shortenrepolarisation, shorten QT, raise fibrillationthreshold e.g. lignocaine, mexilitine,phenytoin
•
Class 1c- no ef ect on action potential or onrepolarization, prolongs PR and QRS e.g.flecainide
•
Class II- beta blockers e.g. propanolol
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Classes of antiarrythmics
•Class III- Potassium channelblockers that prolong durationof action potential e.g.amiodarone, disopryamide
•Class IV- Calcium channel
blockers that have importantef ects on upper and middleparts of the AV node. e.g.
Verapamil
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1. Adenosine (Adenocor)• Purine Nucleoside
• comprise of a molecule of adenineattached to a ribose sugarmolecule via a β-N9 glycosidicbond.
• also acts as a neurotransmitter• when administered I.V., causes
transient heart block in the AVnode
• Via A1 receptor, inhibiting adenylylcyclase, reducing cAMP and socausing cell hyperpolarization byincreasing outward potassium ionflux 15
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2. Lignocaine
•Class 1B antiarrythmic drug
•also act as local anaesthetic.
•
contain amide group in thestructure
•MOA: block the fast voltage
gated sodium (Na+) channels• inhibit sodium influx
• block rise of action potential
• inhibit signal conduction16
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3. Verapamil
•MOA- Calcium ion influxinhibitor
•L-type calcium channel blocker
• relaxation and prevention of coronary artery spasm- dilates
the main coronary arteries andarterioles both in normal andischemic regions. 17
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4. Amiodarone
• Class III antiarrthymic drug
• Blocks sodium channels at rapid pacingfrequencies
• noncompetitive antisymphatetic action
• lengthen cardiac action potential
• negative chronotropic ef ect in nodal tissues
• blocks myocardial potassium channels -->contributes to slowing of conduction and
prolongation of refractoriness in the AV node.• hypotension is the most common adverse ef ect
seen with I.V. amiodarone18
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Procainamide &
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Procainamide &Disopyramide
• Both are Class 1a antiarrythmics
• interfere directly with the depolarization of thecardiac membrane
• Inhibits the fast sodium channels
• Increases the duration of a.p. in cardiac cells
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Disopyramide
Procainenamide
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Propanolol
• A synthetic non selective beta-adrenergicreceptor-blocking agent.
• arrhythmia and thyroid crisis as well ashypertension
• blocks action of the sympathetic nervous system byblocking beta receptors on sympathetic nerves
• highly lipophilic
• undergoes high first pass metabolism by theliver
• only about 25% reaches systemic circulation
• racemic mixture of two enantiomers, R(+)and S (-)
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Metoprolol
• Beta-adrenergic blocking agent
• use also for hypertension, heart pain
• similar to propanolol.
• blocks action of the sympatheticnervous system by blocking beta
receptors on sympathetic nerves• also reduces force of contraction of the heart 23
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Hypertensive
crisis
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1.Hydralazine (Apresoline)•
Direct-acting smooth musclerelaxant
• vasodilator primarily inarteries and arterioles.
•
Relaxing vascular smoothmuscle, reduce peripheralresistance, lower bp.
• MOA: increase guanosine
monophosphate (GMP)decreasing action of secondmessenger IP3, limitingrelease of calcium from SR of smooth muscle.
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2. Labetalol
• mixed alpha/beta adrenergic antagonist
• acute hypertension and hypertensive crisis
• has stereoisomers
• is a racemic mixtures of four isomers.
• Two of these the (S,S)- and (R,S)-isomers areinactive.
• the third (S,R)-isomer is a powerful alpha one
blocker• the fourth (R,R) isomer is a mixed nonselective
beta blocker and selective alpha 1 blocker
• the ratio of alpha:beta block is apporoximately
3:1
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Vasoactive
Drugs
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1. Dopamine
• also act as a catecholamine neurotransmitter inthe brain
• intravenous medication acting on sympatheticnervous system
• precursor for noradrenaline and releases it fromintracardiac adrenergic nerve endings.
• in the periphery, dopamine stimulatesprejunctional dopaminergic DA2-receptors
which results in inhibition of NA release andinturns, facilitates vasodilation.
• ef ects like increased heart rate and bloodpressure 28
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2. Dobutamine
• Sympathomimetic Drug for treatment of heart failure and cardiogenic shock
• Direct stimulation of beta-one receptors of the sympathetic nervous system.
• Clinically used to treat acute but potentiallyreversible heard failure
• acts on the beta1 receptors of the heart toreduce its contractility and cardiac output.
• * Since it does not induce release of NA likeDOPAMINE, it is less prone to inducehypertension 29
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3. Noradrenaline
•also a hormone and aneurotransmitter
•
Potent alpha agonist with somebeta-adrenergic properties
•shown to increase MAP in
patients with hypotensionresistant to fluid resuscitation inpatients with septic shock 30
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Quiz timeText
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Myocardial
Infarction
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1. Streptokinase
• Protein secreted by streptococci• Ef ective thrombolysis medication, MI, PE.
• Fibrinolytics
• There are three domains to Streptokinase, denoted α
(residues 1–150), β (residues 151–287), and γ (residues 288–414). Each domain bindsplasminogen, although none can activateplasminogen independently
• Extra streptokinase --> extra plasmin production
--> break down of fibrin --> dissolve clots
• given IV ASAP after onset of MI to dissolve clots inther heart arteries.
• Note the dif erence in dosage for patients coming in
for MI or PE
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2. Nitroprusside
• Inorganic compound with formula Na2[Fe(CN)5NO].2H2O
• Red Coloured Salt- potent Vasodilator in arterioles(more) and venules.
•
Complex anion with an octahedral ferrous centersurrounded by 5 tightly bound cyanide ligands and alinear nitric oxide ligand.
• Once in the circulation, it break downs to release NO--> activates guanylate cyclase in smooth muscle
and increase cGMP --> stimulate Ca2+ to ER andreduce availibility--> relaxation of smooth muscles--> vessels dilate.
• Good for Heart Failure + Malignant Hypertension 34
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Eclampsia
- Magnesium
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Status
Epilepticus
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1. Phenytoin
• Chemical structure related tobarbiturates
• Antiepiletic
• Stabilize the inactive state of voltagegated sodium channels
• Suppress abnormal brain activity
seen in seizures ---> by reducingthe electrical conductance amongbrain cells 37
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2 Di
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2. Diazepam
• Benzodiazepine group• Commonly for anxiety, insomnia, muscle
spasm and of course seizure includingstatus epilepticus, alchohol withdrawal.
• MOA: enhances the ef ect of neurotransmitter GABA by binding to thebenzodiazepine site on the GABA A receptorleading to CNS depression
• GABA A receptor activated ---> increase inchloride ions influx into cell ---> increasedhyperpolarisation --> hard to achieve ationpotential --> reduce in excitation
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