it is lec

6. Metabolism :

8. Selected Actions of Histamine in Humans H1, H2 H2 H1, H2 H2 (?) H1 H2 H2 H1 H1 H2 H2  TPR Vasodilatation  Blood flow  Blood flow,relaxation Constriction Relaxation Constriction Constriction Vasodilatation  Permeability  SA rate  Force of contraction Atrial & vent automaticity CARDIOVASCULAR Vascular Facial cutaneous Forearm Gastric mucosa Carotid artery Pulmonary artery Basilar artery Coronary artery Other pre & post cap Arterioles Postcapillary venules Heart Receptor Action Organ Tissue

9. Selected Actions of Histamine in Humans H1 Epinephrine release ADRENAL MEDULLA H2 H1 H2 (?) Acid and pepsin secretion, If Relaxation & Contraction (more prominent) Relaxation (?) GASTROINTESTINAL Oxyntic mucosa GI smooth muscle Gallbladder smooth muscle H1, H2 (?) Pain & itching (esp to insect bites & needle stings) CUTANEOUS NERVE ENDINGS (Sensory) H1 H2 Contraction (more prominent) Relaxation RESPIRATORY Bronchiolar smooth muscle H2 Inhibition of IgE – dependent degranulation BASOPHILS Receptor Action Organ Tissue

16. Oldest member More prolonged action  Incidence of drowsiness Chlorcyclizine 4. Piperazine Most potent Not so prone to develop drowsiness More suitable for older patients Sedation/CNS stimulation Chlorpheniramine Pheniramine Chlorphenamine 3. Alkylamine Most specific H1 antagonist  Anticholinergic activity Feeble CNS effects Somnolence GI s/s common Pyrilamine Mepyramine Pyranesamine 2.Ethylenediamine/ Ethylamine Significant antimuscarinic activity Sedation, somnolence  Incidence of GI symptoms Effective in emesis & motion sickness Diphenhydramine First Gen. Agents: 1. Ethanolamine Characteristics Prototype Structural Class

17. Counters motion sickness & emesis Meclizine/Meclozine Counters motion sickness (primarily) Cyclizine Long acting Widely used for skin allergies CNS depressant More prominent antipruritic action Hydroxyzine Characteristics Prototype Structural Class

18. Rhinitis, urticaria (-) pass BBB Cetirizine 3. Piperazine Rapid onset of action (30 mins) (-) anticholinergic effects Reduce both wheal & flare response  Potential to penetrate BBB Skin allergy Allergic rhinitis Acrivastine 2. Alkylamine Highly selective for H1 receptor Non-sedating (-) anticholonergic action (-) pass BBB  incidence of S/E Terfenadine Second Gen.Agents 1. Piperidine Anticholinergic Prominent sedation Counters motion sickness primarily antiemetic Promethazine 5. Phenothiazine Characteristics Prototype Structural Class

36. Pharmacological Properties