4.1 - Autocoids - Histamine Flashcards
– Local Hormones
– Site of action is within the site of secretion
– Produces virtually by ALL cells
Autocoids
Autocoids
- Histamine
- Serotonin
- Eicosanoids
- Bradykinin
Histamine
- Biosynthesis
- Receptors
- Location
- Responses
Biosynthesis
- Precursor
- Locations
- Step
Precursor
L-histidine
Locations
- Mast cells
- Basophils
- Enterochromaffin-like cells
- CNS
Step
L-histidine ➡️1️⃣ Histamine
1️⃣
L-histidine decarboxylase
Receptors
- H1
- H2
- H3
H1
— Gq linked
• Location & Responses
Extravascular SM
bronchial
BrochoCONSTRICTION
Vascular SM
BV
Vasodilation
Sensory Nerve Endings
Pain & Itch
Endothelial cells (Lining of blood vesssels)
Contraction
— ⬆️ capillary permeability
CNS
Stimulation
Triple Response of Lewis
— effects of dermal injection of Histamine
- Red Dot (flush)
- Localized Swelling (wheal)
- Spreading erythema (flare)
H2
— Gs linked
• Location & Responses
Parietal cells (stomach)
– HCl
– Intrinsic Factor
H I P
– Hydralazine
– Isoniazid
– Procainamide
Basal gastric acid secretion
— peak: at night
Mast cells and Basophils
Degranulation
– Histamine release
H3
Presynaptic (CNS)
— inhibition of Histamine Release
Drugs
- Agonists
* Antagonists
Agonists
- Histamine
* Betahistine
– Pulmonary Function Test
– Determine the adequacy of acid secretion (gastric)
Histamine
– H1 agonist
– H3 antagonist
– Mgt of Vertigo
Betahistine (Serc®)
Antagonists
- Physiologic
* Pharmacologic
Physiologic
Epinephrine
– B2 agonist — Dilation
Pharmacologic
— Antihistamines
- H1 Antagonists
* H2 Antagonists
H1 Antagonists
- 1st Gen
* 2nd Gen
1st Gen
— Classical/ Sedating
— Anticholinergic effects
- Ethanolamines
- Ethylenediamines
- Piperazines
- Alkylamines
- Phenothiazine
- Piperidine
Ethanolamines
— Most sedating ‼️
— Significant anticholinergic effects
- Diphenhydramine
- Dimenhydrinate
- Doxylamine
- Carbinoxamine
DOC: Acute Dystonic Crisis (Torticollis)
Diphenhydramine
Salt of Diphen
Dimenhydrinate
– Unisom®
– Sleeping Aid
Doxylamine
Less sedating
Cetirizine
Anti-motion sickness
- Meclizine
* Cyclizine
Components of Alkylamines
Components of cold medication
Alkylamines
- BromPHENIRAMINE
* ChlorPHENIRAMINE
Phenothiazine
Promethazine
— Phenergan®
— Anesthetic agent
PiperiDINE
CyproheptaDINE
— Anti-serotonergic
— Mgt of 5-HY syndrome
2nd Gen
— Less sedating/ Non-sedating
- Less Sedating (Piperazines)
* Non-Sedating (Piperidines)
Less Sedating (Piperazines)
- Cetirizine
* Levocetorizine
Non-sedating (Piperidines)
— For pilots, drivers or workers that requires to be fully awake
- Loratadine
- Desloratadine
- Fedofenadines
Mgt of allergic reactions
– Prevention and Treatment
1st Gen: More effective
Mgt of Parkinsonism & EPS
– Acute dystonia
Diphenhydramine
Sleep Aids
– Unisom®
— Diphenhydramine
— Doxylamine
Mgt of motion sickness
- Meclizine
* Cyclizine
Component of Cold Preparations
Alkylamines
Anesthetic adjuncts
Promethazine
Mgt of 5-HT Syndrome
Cyproheptadine
Mgt of Malignant Hyperthermia
Dantrolene
Mgt of Neuroleptic Malignant Syndrome
- Bromocriptine
* Dantrolene
S/E: H1 Antagonists
- Sedation
- Anticholinergic effects
- Cardiotoxicity
C/I: H1 Antagonists
- BPH
* Glaucoma
H2 Antagonists
- CimeTIDINE — Least potent
- RaniTIDINE
- NizaTIDINE
- FamoTIDINE — Most potent
Uses: H2 ANTAGONISTS
- Mgt of GERD
- Mgt of Acid Peptic Diseases
- DOC in mgt of acute GI ulcer bleeding
- Adjuct in the mgt of allergic reactions
Mgt of GERD
• 1st line: PPIs
— H2 blockers: 60-70%
Mgt of acid peptic diseases
1st line: PPIs
S/E: Cimetidine
– Enzhme inhibition – Anti-andronergic effects - gynecomastia - impotence – ⬆️ prolactin levels (galactorrhea)
Uses: H1 Agonists
- Mgt of Allergic Rxns
- Mgt of Parkinsonism & EPS
- Sleep Aids
- Mgt of Motion Sickness
- Anesthetic Adjunct
- Mgt of 5-HT
Ethylenediamines
- Pyrilamine
* Tripelennamine
PiperaZINES
— Less sedating
- Hydroxyzine — Cetirizine
- Meclizine
- Cyclizine