Chapter 73: Antihistamines Flashcards
Histamine function
- dilates small blood vessels in the vascular system
- constricts smooth muscles in the bronchi
- stimulates acid secretion in the stomach
Histamine is
a neurotransmitter in the CNS
histamine is present
in almost all tissues; especially skin, lungs and GI
histamine has an important role in
- allergic reactions
- regulation of gastric secretions
histamine is stored in
mast cells and basophils in the periphery
histamine is produced by
neurons in the CNS
histmain release can be
- allergic
- nonallergic
allergic release of histamine requires
prior exposure to the allergen
nonallergic release of histamine can be due to
several agents (certain drugs, radiocontrast media, plasma expanders)
H1 receptors functions
- vasodilation
- increased capillary permeability (edema)
- bronchoconstriction
- CNS effects (cognition, memory, sleep-wake cycles)
- itching, pain, secretion of mucus
H2 receptors functions
- secretion of gastric acid by acting directly on parietal cells
what is the principle use of h1 blockers
treatment of mild allergic disorders
- rhinitis, itching, localized edema (h1 receptors)
what is the principle use of H2 blockers
treatment of gastric and duodenal ulcers
H1 antagonists
- blockage of H1 receptors
- used for treatment of mild allergic disorders
H2 antagonists
- blockage of H2 receptors
- used for treatment of gastric and duodenal ulcers
what are the H1 antagonist prototypes
- Diphenhydramine (benadryl) –> first generation
- Cetirizine (reactine) –> second generation
first generation H1 antagonists are
highly sedating
H1 antagonists therapuetic uses
- mild allergy
- severe allergy
- motion sickness
- insomnia
- common cold
H1 antagonists adverse effects
- sedation
- nonsedative CNS effects (dizziness, fatigue, coordination problems, confusion)
- GI effects (nausea, vomiting, loss of appetite, constipation)
what are the sings of toxicity for H1 antagonists
- dilated pupils, flushed face, hyperpryexia, dry mouth, urinary retention
- coma, cardivoascular collapse, death
treatment for overdose of H1 antagonists
- activated charcoal
- cathartic
- Sezuires: IV bensodiazepines (lorazepam, midazolam)
antihistamines are contradicted in
- thired trimester of pregnancy
- nuring mothers
- newborn infants
What are the examples of second generation H1 antagonists
- Cetirizine (reactine)
- Fenofexadine (allegra)
- Loratadine (Claritin)
- Desloratadine (Aerius)
benefits of second generation H1 antagonists
- produce much less sedation
