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Autonomic nervous system-III

  1. Antiadrenergic drugs Dr. Karun Kumar Senior Lecturer Dept. of Pharmacology
  2. General Effects of α blockers Blockade of vasoconstrictor α1 receptors ↓ ↓ TPR ↓ Pooling of blood in capacitance vessels ↓ ↓ venous return and CO ↓ Fall in BP
  3. Interference in postural reflex ↓ Hypotension ↓ Dizziness and syncope • Patients receiving an α blocker should not suddenly stand up after being supine on the dental chair • Reflex tachycardia occurs (↓ mean arterial pressure and ↑ NA due to blockade of presyn α2 receptors)
  4. • Nasal stuffiness and miosis Hypotension ↓ renal blood flow ↓ ↓ GFR & ↑ reabs. of Na+ and water ↓ Na+ retention & expansion of blood volume (accentuated by reflex ↑ in renin)
  5. Tone of smooth muscle in bladder trigone, sphincter and prostate ↓ by blockade of α1 receptors ↓ Urine flow in patients with benign hypertrophy of prostate (BHP) is improved • Contractions of vas deferens and related organs which result in ejaculation are coordinated through α rec. (α blockers can inhibit ejaculation  impotence)
  6. Side Effects
  7. Uses of α blockers 1. Pheochromocytoma  Phenoxybenzamine definitive therapy for inoperable and malignant tumors. • Employed before and during surgical removal of the tumor • Alternatively, Phentolamine drip can be instituted during the operation.
  8. 2. Hypertension  Prazosin and other slective α1 blockers are useful antihypertensive drugs. • Phentolamine helps to control episodes of ↑ BP during Clonidine withdrawal and cheese reaction in patients on MAO inhibitors
  9. Cheese Reaction (DOC  Phentolamine) Cheese, beer, red wine & banana contain tyramine ↓ In presence of MAOI, it escapes degradation ↓ Reaches systemic circulation ↓ Uptake by adrenergic neuron ↓ Enters storage vesicles & displaces NE ↓ Hypertensive crisis
  10. 3. Benign hypertrophy of prostate (BHP)  The urinary obstruction caused by BHP has a static component (↑ size of prostate) and a dynamic component (↑ tone of bladder neck/prostate s.m.) Two classes of drugs are available: 1. α1 adrenergic blockers (Prazosin like)  Decrease tone of prostatic/bladder neck muscles. 2. 5-α reductase inhibitor (Finasteride)  Arrest growth/reduce size of prostate
  11. Classification
  12. Uses of β blockers (THAPPAD) 1. Thyrotoxicosis & Tremors 2. HTN & Hypertrophic cardiomyopathy 3. Angina & Acute MI 4. Prophylaxis of migraine 5. Phaeochromocytoma (along with alpha blockers) 6. Anxiety & Arrhythmias 7. Dissecting aortic aneurysm 8. Digitalis toxicity
  13. Adverse effects of beta blockers (BBC Loses Viewers in Rochedale) • Bradycardia • Bronchoconstriction • Claudication • Lipids (profile altered) • Vivid dreams & nightmares • Negative inotropic action • Reduced sensitivity to hypoglycemia
  14. Contraindications of Propranolol • Don’t Prescribe Him Propranolol 1. Diabetes mellitus 2. Pulmonary diseases (Asthma, COPD) 3. Heart block, bradycardia 4. Prinzmetal’s angina 5. Peripheral vascular disease
  15. Drug Interactions 1. Additive depression of SAN & A-V conduction with Digitalis and Verapamil  Cardiac arrest 2. Propranolol delays recovery from hypoglycaemia due to insulin and oral antidiabetics. Warning signs of hypoglycaemia (tachycardia, tremor) are suppressed 3. Phenylephrine, Ephedrine and other α agonists present in cold remedies can cause marked rise in BP in β blocked subjects
  16. 4. Though only low concentrations of Adr are added to lidocaine for dental anesthesia, it may produce some pressor action in patients receiving nonselective β blockers 5. Indomethacin and other NSAIDs attenuate the antihypertensive action of β blockers 6. Propranolol retards lidocaine metabolism by reducing hepatic blood flow
  17. Other β Blockers • Cardioselective (Metoprolol, Atenolol, Acebutolol, Bisoprolol, Nebivolol) 1. Lower propensity to cause bronchoconstriction 2. Less interference with carbohydrate metabolism 3. Lower incidence of cold hands and feet 4. No/less deleterious effect on blood lipid profile 5. Ineffective in suppressing essential tremor 6. Less liable to impair exercise capacity
  18. Partial agonistic (intrinsic sympathomimetic) (Pindolol, Acebutolol) • Activate β1 and/or β2 receptors submaximally 1. Bradycardia and depression of contractility at rest are not prominent 2. Withdrawal is less likely to exacerbate hypertension or angina 3. Not effective in migraine prophylaxis— dilate cerebral vessels 4. Less suitable for secondary prophylaxis of MI
  19. α + β Adrenergic blockers • Labetalol  5 times more potent in blocking β than α receptors • Causes ↓ BP & no/slight ↓ in HR • Orally effective but undergoes considerable first pass metabolism • Moderately potent hypotensive & is specially useful in pheochromocytoma, clonidine withdrawal; can also be used in essential hypertension • S/E  Postural hypotension
  20. • Carvedilol  β1 + β2 + α1 blocker; produces vasodilatation due to 1. α1 blockade 2. Calcium channel blockade • Has antioxidant property • Use  Hypertension & CHF

Editor's Notes

  1. temporary loss of consciousness caused by a fall in blood pressure.
  2. There are three types of postural reflexes: righting reactions, placing reactions, and equilibrium reactions. Syncope (pronounced “sin ko pea”) is the medical term for fainting or passing out. It is caused by a temporary drop in the amount of blood that flows to the brain. Syncope can happen if you have a sudden drop in blood pressure, a drop in heart rate, or changes in the amount of blood in areas of your body. Fainting or a sudden temporary loss of consciousness.
  3. Orthostatic hypotension is a sudden drop in blood pressure when you stand from a seated or prone (lying down) position. You may feel dizzy or even faint. Orthostatic means an upright posture. Hypotension is low blood pressure. The condition is also called postural hypotension
  4. Phenoxybenzamine [fen-ox-ee-BEN-za-meen] is nonselective, linking covalently to both α1 and α2 receptors . The block is irreversible and noncompetitive, and the only way the body can overcome the block is to synthesize new adrenoceptors, which requires a day or longer. Therefore, the actions of phenoxybenzamine last about 24 hours. After the drug is injected, a delay of a few hours occurs before a blockade develops.
  5. Claudication is pain caused by too little blood flow to your legs or arms. This is usually a symptom of peripheral artery disease, in which the arteries that supply blood to your limbs are narrowed, usually because of atherosclerosis.
  6. A condition in which some areas of the body feel numb and cool in certain circumstances. In Raynaud's phenomenon, smaller arteries that supply blood to the skin constrict excessively in response to cold, limiting blood supply to the affected area. The fingers, toes, ears and tip of the nose are commonly involved and feel numb and cool in response to cold temperatures or stress. It's often accompanied by changes in the colour of the skin. Treatment beyond self-care, such as dressing warmer, usually isn't required.