Antihistamines satya
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this ppt is on pharmacology of histamine&Antihistamines... highlighting the important areas with illustrations and pictures for understanding and remembering easily....
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Antihistamines satya
- 9. PHARMACOLOGY OF HISTAMINE & ANTIHISTAMINES DR. V. SATHYA NARAYANAN MD, PROFESSOR OF PHARMACOLOGY SRM MCH & RC CHENNAI, INDIA
- 10. ∗ Means--- tissue amine ∗ Present mostly within mast cells ∗ Present in tissues ∗ Present in venoms ∗ Synthesized from histidine ∗ Inactive orally HISTAMINE
- 14. ∗ Allergic phenomena ∗ Inflammation ∗ As transmitter ∗ Mediate gastric secretion (HCl) PATHOPHYSIOLOGICAL ROLE
- 21. ∗ Dilates small blood vessels hypotension, headache ∗ Triple response – flush, flare, wheal ∗ Bronchospasm ∗ Increases gastric acidity ∗ pain and itching ACTIONS
- 23. ∗H1 – Smooth muscle, blood vessels, endothelium, brain, lungs ∗H2 – Gastric glands, blood vessels, heart, brain ∗H3 – Brain ∗H4 – eosinophils, neutrophils HISTAMINE RECEPTORS
- 24. ∗ H1 selective histamine analogue ∗ Cause vasodilatation in the internal ear ∗ Used to control vertigo in Meniere’s disease ∗ Orally active ∗ Contraindicated in asthmatics and ulcer patients BETAHISTINE
- 28. ∗Competitively antagonize ∗actions of ∗ histamine ∗ at H1 receptors H1 RECEPTOR ANTAGONISTS
- 33. 1. Highly sedative: Diphenhydramine (Benadryl) Dimenhydrinate Promethazine ( phenergan ) Hydroxyzine CLASSIFICATION
- 35. 2. Moderately sedative: Pheniramine ( avil ) Cyproheptadine Meclizine Buclizine Cinnarizine CLASSIFICATION
- 37. 3. Mild sedative Chlorpheniramine ( piriton ) Methdilazine Mepyramine (Pyrilamine) Dimethindene Triprolidine Mebhydroline Cyclizine Clemastine CLASSIFICATION
- 39. 4. Second generation antihistamines: Fexofenadine ( allegra ) Loratadine ( lorfast ) Desloratadine Cetirizine ( cetzine ) Levocetirizine Azelastine Mizolastine Ebastine CLASSIFICATION
- 42. Histamine antagonism: ∗ Blocks histamine induced bronchoconstriction, intestinal contraction, vasodilatation, fall in BP, triple response ( wheal, flare, itch ) ∗Gastric secretion not affected PHARMACOLOGICAL ACTIONS
- 47. ∗ Suppress manifestations of immediate hypersensitivity reactions ∗ (Urticaria, ∗ itching, ∗ angiooedema are well controlled) ∗ Partially prevents anaphylactic fall in BP ∗ Asthma practically unaffected ANTIALLERGIC ACTION
- 53. ∗ Sedation and CNS depression (older antihistamines) ∗ Impaired concentration, coordination ∗ Some experience restlessness and insomnia ∗ Toxic doses produce ∗ excitement ∗ convulsions CNS
- 57. TOXIC DOSES
- 58. ∗ Antagonise muscarinic actions of acetylcholine Dryness of mouth constipation urinary retention Blurring of vision ∗ Add anticholinergic effects of atropine, Phenothiazines ANTICHOLINERGIC ACTION
- 60. ∗ Well absorbed from oral, parenteral routes ∗ Widely distributed and enter brain (Except newer compounds) ∗ Duration of action of most is 4-6 hours, newer drugs 12-24 hrs ∗ Metabolized in the liver ∗ Excreted in urine PHARMACOKINETICS
- 62. ∗Sedation, ∗ diminished alertness and concentration ∗ Motor incoordination, ∗ fatigue, ∗ tendency to fall asleep ∗ Impaired psychomotor performance (CAUTION – DRIVING, OPERATING MACHINERY) ADVERSE DRUG REACTIONS
- 67. ∗ Anticholinergic side effects ∗ Headache ∗ Some are teratogenic ∗ (Cyclizine, fexofenadine) ADVERSE DRUG REACTIONS
- 70. ∗ Synergism with alcohol and ∗ Other CNS depressants more CNS depression DRUG INTERACTIONS
- 72. ∗ RELIEVES ONLY SYMPTOMS ∗ hay fever ∗ Atopic and contact dermatitis ∗ Eczema ∗ Bee and wasp stings ∗ Mild blood transfusion reactions ∗ Allergic conjunctivitis ∗ Urticaria ∗ Angioedema THERAPEUTIC USES 1. ALLERGIC DISORDERS
- 73. hay fever
- 84. ∗ Afford symptomatic relief ∗ by anticholinergic and ∗ sedative actions ∗ Do not affect course of the illness COMMON COLD
- 86. ∗ Promethazine, Diphenhydramine are useful ∗ Prevent motion sickness ∗ Promethazine (Phenergan) is useful in morning sickness ∗ Drug induced vomiting ∗ Postoperative vomiting ∗ Radiation sickness AS ANTIEMETIC
- 92. ∗ Cinnarizine is useful ∗ It modulates Ca++ fluxes ∗ Have additional anticholinergic, sedative, vasodilator property ∗ Widely used ∗ Useful in Meniere’s disease ∗ Side effects are sedation and GI upset VERTIGO
- 94. ∗ Diphenhydramine and promethazine are useful ∗ Drug - induced acute dystonias are ∗ treated with parenteral promethazine, ∗ trihexyphenidyl PARKINSONISM
- 97. ∗ As hypnotics -- specially in children ∗ (diphenhydramine and promethazine) ∗ likely to depress respiration ∗ Not as dependable as benzodiazepines ∗ Hydroxyzine is used in anxiety with autonomic symptoms AS SEDATIVE, HYPNOTIC, ANXIOLYTIC
- 100. ∗ As antitussive in cough ∗ Afford symptomatic relief ∗ (diphenhydramine- benadryl cough formula) ∗ Preanaesthetic medication - promethazine OTHER USES
- 104. ∗ H1 receptor blockers marketed after 1980 ∗ Have higher H1 selectivity ∗ No CNS depression ∗ No anticholinergic side effects ∗ Act by additional antiallergic mechanisms SECOND GENERATION ANTIHISTAMINICS
- 108. ∗ No sleepiness ∗ Do not impair psychomotor performance ∗ (not contraindicated in drivers) ∗ Do not potentiate alcohol or benzodiazepines ∗ Have long duration of action ADVANTAGES
- 111. ∗ Have narrow spectrum of usefulness ∗ Have poor antipruritic , antiemetic action ∗ Poor antitussive ∗ Expensive DISADVANTAGES
- 112. ∗ First SGA ∗ When CYP3A4 inhibitors (like erythromycin, ketoconazole) are administered concurrently produces fatal polymorphic ventricular tachycardia (torsades de pointes) ∗ WITHDRAWN by most manufacturers TERFENADINE
- 116. ∗ Active metabolite of terfenadine ∗ Does not produce torsades de pointes ∗ Not entirely safe ∗ Does not cross BBB ∗ Free of anticholinergic side effects ∗ Duration of action 24 hrs ∗ Caution in patients with long QT interval, bradycardia, hypokalemia ∗ Available as allegra FEXOFENADINE
- 119. ∗ Selective peripheral H1 antagonist ∗ No CNS action ∗ Faster acting ∗ Long acting ∗ Does not produce Torsades de pointes ∗ No interaction with macrolides or Ketoconazole ∗ Highly effective in urticaria and atopic dermatitis LORATADINE
- 120. ∗ Active metabolite of loratadine ∗ Effective at half the dose ∗ No CNS effect ∗ No cardiac ADR DESLORATADINE
- 121. ∗ Penetrate brain poorly ∗ Not metabolized ∗ Also inhibits release of histamine – extra benefit in allergic disorders ∗ Higher and longer lasting concentration in skin ∗ Once daily dose ∗ Does not produce arrhythmias ∗ Levocetirizine effective at half the dose CETIRIZINE
- 125. ∗ has good topical activity ∗ inhibits histamine release and inflammatory reaction triggered by LTs, PAF ∗ bronchodilator ∗ Downregulate ICAM – 1 expression ∗ Long acting ∗ Given by nasal spray for allergic rhinitis ∗ Side effects – stinging , altered taste AZELASTINE
- 128. ∗ Non sedating newer SGA ∗ Produces active metabolite ∗ Active in nasal and skin allergies ∗ Prolong Q-Tc interval can cause arrhythmias EBASTINE
- 130. ∗ Recently introduced ∗ Also a PAF antagonist ∗ Indicated in allergic rhinitis RUPATADINE
- 132. ∗ Adrenaline – Physiological antagonist ∗ – life saving in anaphylactic shock ∗ Release inhibitors – ∗ Cromolyn – used in asthma OTHER HISTAMINE ANTAGONISTS
- 134. ∗ Histamine is an autacoid , act locally, ∗ Mediate allergic reactions, through histamine receptors ∗ Antihistamines block H1 receptors ∗ Produce anti allergic effects, CNS depression, Anticholinergic effects ∗ Classified according to sedative property ∗ New generation antihistamines (IInd generation ) devoid of sedation, anticholinergic effects ∗ Cetirizine is commonly preferred SUMMARY