Antihistamines

Antihistamines Actions of histamine on H1 and H2 receptors Increase production of nasal and bronchial mucus (H1) Constriction of bronchioles results in symptoms of asthma (H1) Action on sensory nerve endings causes itching and pain (H1)

Lowers systemic blood pressure by reducing peripheral resistance (H1,H2) Reddening of the skin due to local vasodilation (H1,H2) Stimulation of gastric Hcl secretion(H2 )

Histamine antagonists adrenaline antihistamines corticosteroids

It is the main physiological antagonist that antagonizes the effects of histamine by producing opposite effects. It causes bronchodilatation and vasoconstriction Blocks histamine receptors and prevent histamine from reaching its sites of actions. (used in acute and chronic allergic conditions) They stabilize mast cells and prevent the formation and release of histamine.they are used in severe acute conditions (with adrenaline)and in chronic conditions with antihistamines

First generation ( sedating) Clemastine Doxylamine Mequitazine(primalan)R Dimetindene Cyclizine(emetrex)R Dimenhydrinate

Chlorpheniramine Chlorphenoxamin e Pheniramine(avil)R Cyproheptadine Diphenhydramine promethazine

Chlorphenoxamine(allergex)R

Second generation ( nonsedating) Fexofenadine Acrivastine Desloratadine Loratadine Ebastine

Desloratadine (desa)R

Cetirizine Levocetirizine terfenadine

acrivastine(semprex)R

pharmacokinetics .the onset of action occurs within 1 to 3 hours-1 The duration of action for many oral H1 antihistamines is at least 24 hours,facilitating once-daily -2 dosing. They are most effective when used prophylactically before allergen exposure rather than as .needed . Tolerance to the action of H1 antihistamines has not been observed-3

Therapeutic uses Allergic and inflammatory-1 conditions (allergic rhinitis and urticaria)

Motion sikness and nausea-2 Treatment on insomnia-3 Diphenhydramine(sultan)R Diphenhydramine Dimenhydrinate(dramenex)R Doxylamine(donormyl)R R Cyclizine(emetrex) Promethazine(phenergan)R antihistamines are frequently used in combination preparations for the treatment of coughs and -4 colds The mechanism of their antitussive action may involve reduction in cholinergic nerve transmission or may simply result from their sedative effects .cyproheptadine is used for prophylaxis of migraine and also increase appetite -5 antihistamines are the drugs of choice in controlling the symptoms of allergic rhinitis and urticaria, because histamine is the principal mediator However, the H1 –receptor blockers are ineffective in .treating bronchial asthma, because histamine is only one of several mediators of that condition although the margin of safety is high and chronic toxicity is rare, acute poisoning is common .especially in young children

Adverse effects of sedating antihistamines First-generation H1 -receptor blockers have a low specificity; that is, they interact not only with histamine receptors but also with muscarinic cholinergic receptors, α-adrenergic receptors, and serotonin receptors The extent of interaction with these receptors and, as a result, the nature of the side effects vary with the structure of the drug. Some side effects may be undesirable, and others may have therapeutic value

cholinergic

α-adrenergic

↑dry mouth ↑urinary retention ↑sinus tachycardia

↑hypotension ↑dizziness ↑reflex tachycardia

serotonin ↑appetite

Histamine H1 ↓allergic inflammation, itching,rhionrrhea ↓neurotransmission in the CNS ↑sedation

Sedating antihistamines should be avoided in severe liver disease as they increase risk of coma Most manufactures of antihistamines advise avoiding use during pregnancy however, there is no evidence of teratogenicity except for hydroxyzine and loratadine

‫البمبولت‬ drug Active constituent

pirafene

tavegyl

avil

chlorpheniramine

clemastine

pheniramine

‫النقط‬ drug

Fenistil zyrtec

Active constituent Dimetindene ‫ جرقعات‬3 ‫الجرقعة بمقسمة قعلى‬ Cetrizine ‫جرقعة واحدة يوبميا او بمقسمة قعلى جرقعتين‬

dose ‫بملقعق‬3-1 ‫ نقطة او‬30 – 10 ‫اقل بمن سنة‬ ‫بملقعق‬4-3 ‫ نقطة او‬45 – 30 ‫ سنوات‬3 ‫بمن سنة الى‬ ‫ بمل شراب‬5 ‫ نقط او‬10 ‫ سنوات‬6 ‫ ال‬3 ‫بمن‬ ‫ بمل بمساءا‬2.5 ‫ بمل صباحا و‬2.5 ‫يمكن تقسيمها‬

‫ بمل شراب‬10=(‫بملليلتر‬1) ‫ نقطة‬20 = ‫القرص‬ Active constituent Chlorpheniramine Clemastine Cyproheptadine Dimenhydrinate

drug

dose

Allergyl ,anallerge,pirafene

‫ بمرات يوبميا‬3 ‫الكبار قرص‬ ‫بمرتين يوبميا‬ ‫الفطفال بمعلقة صغيرة‬ ‫ بمل شراب‬5 ‫ الى‬2.5 ‫ سنوات‬3 ‫ الى‬1 ‫بمن‬ ‫ بمل شراب‬5 ‫ سنوات‬6 ‫ الى‬3 ‫بمن‬ ‫ سنوات بملعقة صغيرة‬7 ‫ الى‬2 ‫بمن‬ ‫ بملعقة صغيرة‬2 ‫ قرص واحد او‬14 ‫ الى‬7 ‫بمن‬ ‫ بمرات يوبميا أو قبل السفر‬3 ‫ الى‬2 ‫قرص‬ ‫بنصف ساقعة‬ ‫)ست سنوات فاكثر قرص واحدة او بملعقتين‬.. ‫كجرقعة واحدة)او تقسم قعلى جرقعتين بملعقة‬ (‫او نصف قرص صباحا وبمساءا‬ ‫ بمل كجرقعة‬5 ‫ سنوات بملعقة واحدة‬3-6).. ( ‫واحدة او تقسم قعلى جرقعتين‬ ‫ بمل بمرة واحدة يوبميا‬2.5 ‫ سنين‬2-5 ‫ بمل بمرة واحدة يوبميا‬5 ‫ سنة‬6-11 ‫قرص بمرة واحدة يوبميا‬ ‫ سنة فاكثر‬12 ‫الكبار قرص بمرة واحدة يوبميا‬ ‫بمل بمرة واحدة يوبميا‬5 ‫الفطفال بملعقة صغيرة‬ ‫الكبار قرص بمرة واحدة يوبميا‬

Tavegyl ‫بمرتين يوبميا‬ Triactin ‫ بمرات يوبميا‬3 – 2 Dramenex

Cetirizine

Zyrtec,cetrak,histazine,tomazine

Ebastine

Evastine,ebastel,astin,bastab

Loratadine Fexofenadine

Claritine,lorano,loratan,mosedin Alertam,allerfen,fastel,telfast.rapido

(‫)جرقعة الدوية المضادة للحساسية التى تسبب النعاس بمرتين يوبميا( )والتى ل تسبب النعاس تستخدم بمرة واحدة وقد تقسم قعلى جرقعتين‬