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Adrenergic drugs (VK)
 

Adrenergic drugs (VK)

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    Adrenergic drugs (VK) Adrenergic drugs (VK) Presentation Transcript

    • SYMPATHETIC NERVOUS SYSTEM (ADRENERGICS)
    • SYMPATHOMIMETIC  Sympathomimetic drugs mimic the effects of sympathetic nerve stimulation  Also adrenergic agonists  Adrenergic receptors
    • Adrenergic Agonists  Chemical classification Catecholamines  Non-catecholamines 
    • Adrenergic Agonists Differences Catecholamine  Cannot use orally  Cannot cross BBB Short-half live Examples: Norepinephrine Epinephrine Isoproteronol Dopamine Dobutamine Noncatecholamines  Can use orally  Can cross BBB Longer half life Examples: Ephedrine Phenylephrine Terbutaline
    • ENDOGENOUS CATECHOLAMINES Naturally occurring in body:  Norepinephrine -Sites: postganglionic sympathetic sites (except sweat glands , erector pillorie, hair follicles, )  Epinephrine- Secreted by adrenal medulla  Dopamine- Major transmitter in basal ganglia, CTZ, limbic system, anterior pitutory.
    • SYNTHESIS
    • Catecholamine s In dopaminergic neurons, synthesis stops here Final step only in adrenal medulla and CNS neurons Tyrosine ↓ Dopa ↓ Dopamine ↓ Norepinephrine ↓ Epinephrine In noradrenergic neurons, synthesis stops here
    • STORAGE, RELEASE, UPTAKE L-Phenylalanine Hepatic hydroxylase
    • Adrenergic Receptors These are mainly 2 types (α) Alfa (β) Beta These are again subdivided into various types 
    • ADRENERGIC RECEPTORS
    • ADRENERGIC DRUGS Symphathomimetics  DIRECT SYMPHATHOMIMETICS         INDIRECT SYMPHATHOMIMETICS    Adrenaline Noradrenaline Isoprenaline Phenylephrine Methoxamine Salbutamol Xylometazoline Tyramine Amphetamine MIXED SYMPHATHOMIMETICS    Ephedrine Dopamine Mephenteramine
    • THERAPEUTIC CLASSIFICATION OF ADRENERGIC DRUGS Pressor agents Noradrenaline Ephedrine Dopamine Phenylephrine Methoxamine Mephentermine Cardiac stimulants Adrenaline Isoprenaline Dobutamine Bronchodilators Adrenaline Isoprenaline Salbutamol (Albuterol) Terbutaline Salmeterol Formoterol Bambuterol
    • Nasal decongestants Phenylephrine Xylometazoline Oxymetazoline Naphazoline Pseudoephedrine Phenyl propanolamine CNS stimulants Amphetamine Dexamphetamine Methamphetamine Anorectics Fenfluramine Dexfenfluramine Sibutramine Uterine relaxant and vasodilators Ritodrine Isoxsuprine Salbutamol Terbutaline
    • PHARMACOLOGICAL ACTIONS Cardiac effects  Positive chronotropic effect   Positive dromotropic effect   An action that increases heart rate An action that speeds conduction of electrical impulses (↑ conduction velocity through AV node) Positive inotropic effect  An action that increases the force of contraction of cardiac muscle
    • Cardiac effects of epinephrine Cardiac output is determined by heart rate and stroke volume CO = HR x SV Epi→ β1receptors at SA node→↑HR Epi→ β1receptors on ventricular myocytes→ ↑ force of contraction
    • vascular smooth muscle α1   In blood vessels supplying skin, mucous membranes, viscera and kidneys, vascular smooth muscle has almost exclusively alpha1-adrenergic receptors Also biphasic response
    • Biphasic Response α1+β1 effect (A) β2 effect (at low doses) Mainly α -action (B) α Blocker E β Blocker β2 effect E
    • vascular smooth muscle  In blood vessels supplying skeletal muscle, vascular smooth muscle has both alpha1 and beta2 adrenergic receptors α1 α1 stimulation β2 β2 stimulation
    • Effects of epinephrine on blood vessel caliber α1   Blood vessels to skin, mucous membranes, viscera and kidneys Stimulation of α1adrenergic receptors causes constriction of vascular smooth muscle
    • Effects of epinephrine on blood vessel caliber: skeletal muscle   At low plasma concentrations of Epi, β2 effect predominates→ vasodilation At high plasma concentrations of Epi, α1 effect predominates→ vasoconstriction α1 β2
    • Effects of Epi on arterial blood pressure Arterial BP = CO x PVR Epinephrine:  ↑ CO  Low doses ↓ PVR (arteriolar dilation in skeletal muscle)  High doses ↑PVR
    • Effects of epinephrine on airways  Epi→β2-adrenergic receptors on airway smooth muscle→ rapid, powerful relaxation→ bronchodilation
    • Effects of epinephrine in the eye  α1 β2 Epi at α1adrenergic receptors on radial smooth muscle → contraction→ mydriasis  Epi at B2adrenergic receptors→ relaxation of ciliary muscle
    • OTHER SYSTEMS       GIT: Peristalsis is reduced, sphincters are contracted. Bladder : Detrusors relaxed, trigone contracted Splenic capsule : Contracts (alpha action), RBCs are poured Skeletal muscle : Neuromuscular transmission is facilitated. (Tremors due to beta 2 actions) CNS: Restlessness , tremors , fall in BP and bradycardia Metabolic : Hyperglycemia, lipolysis
    • Mnemonic for therapeutic uses of adrenaline ABCDEG A- Anaphylactic shock B- Bronchial asthma C- Cardiac arrest D- Delay absorption of local anesthetics E- Epistaxis, Elevate BP G- Glaucoma Others : Reduce nasal congestion, Induces mydriasis
    • Epinephrine (contd..)  Adverse effects of epinephrine Hypertensive crisis Dysrhythmias Angina pectoris Necrosis following extravasation Hyperglycemia
    • Dopamine (DA)  Dopaminergic neurons in brain, enteric nervous system and kidney  Dopaminergic receptors in brain, mesenteric and renal vascular beds
    • Dopamine  Moderate doses DA:  Stimulate DA receptors in mesenteric and renal vascular beds → vasodilation  Stimulate β receptors in heart → ↑HR and 1 ↑force of contraction  High doses DA:  Stimulate α 1 receptors → vasoconstriction
    • Therapeutic uses  Shock (moderate doses)  ↑ blood flow to kidney and mesentery  ↑ cardiac output  Refractory congestive heart failure  Moderate doses ↑ cardiac output without ↑PVR
    • Synthetic Catecholamines: Isoproterenol  Very powerfully stimulates β1- and β2adrenergic receptors  β1 SA nodal cells→↑HR β1 AV nodal cells→↑ conduction velocity No significant effect at α1-adrenergic receptors β1 Ventricular muscle cells→ ↑ force of contraction
    • Synthetic Catecholamines: Isoproterenol  Very powerful β-adrenergic receptor agonist; no effect at α-adrenergic receptors α1 α1 stimulation β2 β2 stimulation
    • Isoproterenol ↓arterial BP = ↑CO x ↓↓PVR Decreased arterial blood pressure triggers autonomic reflex arc
    • Autonomic reflex arc: baroreceptor reflex
    • Cardiovascular control center in medulla Carotid and ↓BP aortic Carotid and baroreceptors aortic ↓BP baroreceptors Isoproterenol ↑ Sympathetic outflow→↑NEpi β1 ↑↑HR ↓ Parasympathetic outflow→↓ACh Reflex tachycardia ↑↑SV + dromotropic effect
    • Effects of isoproterenol on airways  Powerfully stimulates β2-adrenergic receptors on airway smooth muscle→ rapid, powerful relaxation→ bronchodilation
    • Therapeutic uses: isoproterenol   Bronchodilator Complete AV block (3rd degree heart block)
    • Synthetic Catecholamines: Dobutamine    It’s a derivative of DA but not a D1 or D2 receptor agonist Stimulates β1- and β2-adrenergic receptors, but at therapeutic doses, β1-effects predominate Increases force of contraction more than increases heart rate ↑CO = ↑HR x ↑ ↑ SV
    • Dobutamine: Therapeutic uses     Shock MI Cardiac surgery Refractory congestive heart failure
    • Major toxic effects of catecholamines  All are potentially arrhythmogenic     Epi and isoproterenol more arrhythmogenic than dopamine and dobutamine Some can cause hypertension Epinephrine, in particular, can cause CNS effects – fear, anxiety, restlessness Dobutamine can cause vomiting and seizures in cats – must be used at very low doses
    • Adverse effects  CNS:  Restlessness  Palpitation  Anxiety, tremors  CVS:  Increase BP….cerebral haemmorrhage  Ventricular tachycardia, fibrillation  May precipitate angina or AMI
    • Non-catecholamine direct-acting adrenergic agonists Ephedrine Stimulates α1-, β1 and β2-adrenergic receptors and ↑ NE release from noradrenergic fibers  Repeated injections produce tachyphylaxis  It is resistant MAO, orally  Longer acting (4-6), cross BBB 
    •  Marketed as dietary supplement promoted to aid weight loss, ↑ sports performance and ↑ energy. Ingredient in OTC nasal decongestants and bronchodilators Uses : Mild chronic Bronchial asthma, hypotension during spinal anaesthesia ,occasionally for postural hypotension  Sale prohibited by FDA in 2004 due to risks of life-threatening cardiac arrhythmias, stroke and death
    • Non-catecholamine direct-acting adrenergic agonists: Phenylpropanolamine (PPA)     Actions much like ephedrine in the PNS In veterinary medicine, used to treat urinary incontinence in dogs Available in OTC products for treatment of nasal decongestion and as appetite suppressant FDA has requested all companies discontinue marketing products containing PPA due to risk of hemorrhagic stroke
    • α1 –adrenergic receptor agonistcontraction urethral smooth muscle β2 –adrenergic receptor agonist –relaxation detrusor muscle
    • β2-selective adrenergic agonists β2-adrenergic receptors on bronchial smooth muscle Preferential affinity for β2adrenergic receptors, but at sufficiently high doses, can stimulate β1 terbutaline , albuterol inhalation aerosol Relax bronchial smooth muscle→bronchodilation Treatment of asthma, chronic bronchitis
    • β2-selective adrenergic agonists  Due to selectivity for β2 receptors at recommended doses, little-to-no direct stimulation of β1 receptors in heart  Inhalant administration maximizes local effect and minimizes systemic effects
    • Mephenteramine  It is mixed sympathomimetic  COP, BP, heart rate are increased  Active orally with longer DOA (2-6 hrs),can crosses BBB Uses:   To treat hypotension due to spinal anesthesia and surgical procedures Shock in MI and other hypotensive states
    • USES Vascular Hypotensive states  Shock: hemorrhagic/ hypovolemic, spinal, neurogenic, cardiogenic, anaphylactic shock.  Postural hypotension- in parkinsonism, diabetes mallitus  Along with local anaesthetics  To control local bleeding  Nasal decongestants  Peripheral vascular diseases Cardiac  Cardiac arrest  Partial AV block  Congestive heart failure 
    • Bronchial asthma  Acute severe bronchial asthma Allergic disorders  Urticaria, angiodema, anaphylaxis Mydriatics  Fundus examination  Wide angle glaucoma CNS uses  ADHD  Narcolepsy  Epilepsy  Parkinsonism  Obesity Uterine relaxant
    • Adrenergic Agonists  Indirect: Cause NE release only  Example:   Amphetamine CNS stimulant  Increases BP by alpha effect on vasculature, beta effect on heart 