What is the mechanism of action for H1 antihistamines?
Competitive blockade of H1 receptors (antagonist)
What are the clinical uses of H1 antihistamines?
- Allergic rhinitis
- Off label uses: motion sickness, nausea, sleep aid
What are the CNS effects that H1 antihistamines produce?
- Produce depression (sleepiness)
- Treat motion sickness
What are the autonomic and peripheral nervous systems effects in H1 antihistamines?
Autonomic - Blocks constriction of respiratory smooth muscle
Peripheral - Blocks flare (wheals) and itch
What do most antihistamines cause?
- Xerostomia (dry mouth)
- Dry mucus membranes
What did older antihistamines cause?
What are the 2 types of antihistamines?
What type of antihistamine is diphenhydramine (Benadryl)?
What type of antihistmaine is chlorpheniramine (Chlor-Trimeton)?
Why is diphenhydramine (benadryl) included in the dental office emergency kit?
It can be used for allergic reactions/anaphylaxis - IV, IM or tablet
Why would chlorpheniramine (Chlor-Trimeton) be included in the dental office emergency kit?
Allergic reactions/anaphylaxis - IM or IV
What antihistamine is approved for treatment of all types of allergens and sold OTC?
What is the main side effect of cetirizine?
What are some of the non-sedating antihistamines?
- loratadine (Claritin) - OTC
- fexofenadine (Allegra) - OTC
- desloratadine (Clarinex) - (second generation version of Claritin)
Whats the difference with sedating and non-sedating antihistamines?
Non-sedating antihistmaines have a longer onset time and last longer.
What is the mechanism of action of H2 antihistmaines?
Competitive blockage of H2 receptors (GI tract)
Inhibits basal and nocturnal gastric acid secretion (evoked by histamine)
What are H2 antihistamines clinically used for?
- Peptic ulcer
- Hypersecretion of gastric acid
- Zollinger-Ellison syndrome (gastrin producing tumor causing hypersecretion of stomach acid)
What are the H2 antihistamines? and what do they all end with?
Ends with "...tidine"
- cimetidine (Tagamet)
- famotidine (Pepcid)
- Nizatidine (Axid)
- Ranitidine (Zantac)
What happens if you only take H2 antihistamines for peptic ulcers?
The antihistamines promote healing of peptic ulcers - but they will continue if the H pylori (which causes the ulcers) is not treated
What's the main H2 antihistamine adverse effect seen in elderly individuals?
Confusion, slurred speech, delirium and hallucinations
What is the safest of all antihistamines used for GI indications?
ranitidine - Zantac
What is the most dangerous antihistamine?
cimetidine - Tagamet
Inhibits cytochrome P450 to slow the clearance and increases the serum levels of many drugs - which increases the risk for overdose reactions
What type of drug is cromolyn (Gastrocrom)?
Mast Cell Stabilizer
How do mast cell stabilizers work?
They inhibit degranulation, preventing histamine release from IgE sensitized mast cells