Pharm for Hypersensitivity Reactions Flashcards
What are the two categories of drugs for allergic rhinitis
1) Preventers: used for prophylaxis
2) Relievers: used for acute symptom relief
What are types of preventers are there for Allergic Rhinitis
1) Antihistamines (ie diphenhydramine)
2) Intranasal corticosteroids (ie fluticasone)
3) Mast cell stabilizers/ trying to desensitize from releasing histamine (ie cromolyn)
4) Leukotriene Receptor Antagonists (Montelukast)
What are types of relievers are used for Allergic Rhinitis
1) Decongestants: sympathomimetic agents given through oral and nasal routes (ie pseudoephedrine, oxymetazoline): mimic fight/flight SNS
2) Anticholinergics: allow for unopposed sympathomimetic activity to cause vasoconstriction (ipratropium): block PNS
Pharmacotherapy Considerations for Allergic Rhinitis
Treatment will sometimes exceed symptom duration/resolution: want to get symptoms under-control to make sure that the allergic cells are as desensitized as much as possible
Often use “controllers” to stabilize allergy cells and desensitize and achieve control and then switch to a med that can maintain control.
How do antihistamines work
H1 receptor sits on the mast cell: H1 receptor antagonists block histamine receptors associated with inflammation
Where are H2 receptors located
In the stomach, produce more stomach acid
What are the older antihistamines called
1st Generation
Newer is called 2nd generation
When do you use antihistamines
allergic rhinitis, urticaria, minor allergies
adjunct theory for anaphylaxis
vertigo and motion sickness (we have histamine receptors in our ears)
Mechanism of action for antihistamines (ie diphenhydramine/Benadryl)
First generation antihistamine
Antagonizes the H1 receptors, by competing with free histamine for receptor sites, preventing vasodilation associated with histamine
antagonizes M2 acetylcholine receptors
What are adverse effects for antihistamines (ie diphenhydramine/Benadryl)
Unpredictable!
Sedation, difficulty concentrating/confusion
Ataxia (altered balance/movement)
Anticholinergic effects (CANT see, pee, spit, or shit)
Increase HR
Photophobia, blurred vision
Temporary erectile dysfunction
Results in light headiness, orthostatic instability, confusion, possible increased IOP (glaucoma)
Who is most effected by anticholinergic effects
Older people
imbalance in our CNS, so we have more sensitivity in our muscarinic receptors and more acetylcholine
More sensitive in us triggering this imbalance
Increase in fall risk!
Who do we need to be cautious with antihistamines
Heart or arrhythmia issues
What conditions are Secondary Generation Cetirizine (Reaction)
Allergic rhinitis, anaphylaxis, allergic conjunctivitis
Why do we tend to use Secondary Generation Antihistamines more now
favour H1 receptor and not the muscarinic receptors so we can get away from the anticholinergic receptors.
But there can be some minor anticholinergic effects.
What is the mechanism of action for Secondary Generation Cetirizine (Reaction)
Competes with histamine for binding to H1 rector sites (same as first gen)
side effects = same or better
What is fluticasone (Flonase) used for
Intranasal glucocorticoid
Seasonal and perennial allergic rhinitis
What is the mechanism of action for fluticasone (Flonase)
Binds to glucocorticoid receptor, promoves anti-inflammatory effects
Inhibits histamine release by mast cells
Prevents macrophage accumulation
Reduces leukotriene release
What are adverse effects for fluticasone (Flonase)
Very few when applied topically (little systemic absorption)
Local burning, bitter taste
Headache
Epistaxis
Serious adverse effects for diphenhydramine
With high doses, prolonged OT interval on ECG that can lead to cardiac arrhythmias including tornadoes de pointes
Increased IOP (closed angle glaucoma)
Serious adverse effects for fluticasone (Flonase)
Swallowing large amounts can cause systemic adverse effects associated with glucocorticoids
Mode of action for mast cell stabilizers (Cromolyn)
Drugs that inhibit Ca+2 entry into mast cells, which reduces release of histamine and leukotrinenes from Mast cells.
Can take several days to start working.
How are mast cell stabilizers (Cromolyn) taken
Poor BioAvail so eye drops or inhaled (nebules)
What are the side effects for mast cell stabilizers (Cromolyn)
Very few with similar efficacy to antihistamines but delayed onset especially for sever symptoms
Leukotriene Receptor Antagonists (Montelukast) mode of action
Blocks action of leukotriene D4 (LTD4), reducing inflammation and bronchoconstriction associated with LTD4
Also considered a antihistamine
Usually used as a controller type drug for asthma
Few adverse effects
Types of decongestants for allergic rhinitis
1) Sympathomimetic agents
2) Intranasal route (ie Oxymetazoline)
3) Oral route (ie. pseudoephedrine)
How do sympathomimetic agents work
Alpha receptor agonist -> cause vasoconstriction because if we step on the SNS in our periphery to get blood to our core
Promote constriction of nasal blood vessels
Increase HR,
Use in caution with those who have diabetes because there will be spikes in sugar
How do intranasal decongestants (ie Oxymetazoline) work
Immediate relief, used for 3 to 5 days
Sudden discontinuation of drug can cause rebound congestion
Few adverse effects: dry nasal passage, rebound congestion
How do oral route decongestants (ie pseudoephedrine)
Slower onset of action
Rebound congestion does not typically occur upon discontinuation
Risk for systemic adverse effects
Pharmacology of Anaphylaxis
Managing symptoms of anaphylaxis and preventing further inflammation
Symptomatic relief provided by sympathetic agents such as epinephrine
Anti-inflammatory drugs include antihistamines and systemic glucocorticoids
What is Epinephrine (Adrenaline) used for
Anaphylaxis
Hypotension
Dysrhymias (severe ventricular dysrhythmias, bradycardia, systole)
Severe Asthma
Epinephrine (adrenaline) mode of action
Parenteral route
Non-specific adrenergic agonist with action at alpha1, beta1, and beta2 receptors which increases BP and opens airway
Alpha1
vasoconstriction
Beta1
Increased HR, force of contraction
Beta2
Bronchodilation
Adverse effects for Epinephrine (adrenaline)
Hypertension, dysrhythmias are a risk so careful monitoring is crucial
Sympathetic effects include: dry mouth, nausea, vomiting, palpitations, blurred vision, headaches
Extravasation of epinephrine into tissues can cause irritation, tenderness and even ischemia
What is used when extravasation happens
Alpha antagonists such as prazosin
