Antihistaminics Flashcards
Describe histamine’s biological effects.
- Promotes vascular permeability: runny nose, watery eyes, swollen lids, papillae
- Induces vasodilation: redness, headache, hypotension, reflex tachycardia
- Causes smooth muscle contraction: bronchoconstriction
- Stimulates sensory nerves: pain & itching, sneezing
True or false: Antihistaminics are inverse agonists.
True.
What is the most common site of ocular allergy?
Conjunctiva.
- Followed by lids and then the cornea.
Describe the characteristics of Innate Immune response.
- Non-specific and acute
- Lacks memory
- Non-classical complement cascade pathway (no antibodies)
- Common to most life forms
- Involves killer T cells and Macrophages
- Occurs in less than 12hrs
Describe the characteristics of Adaptive Immune response.
- Requires prior exposure to the antigen
- Is an specific and has memory
- Activates classical cascade pathway
- Found exclusively in jawed vertebrates
- Involves cloned memory B&T cells
- 1-2 weeks response time
- will cause a more robust response upon subsequent exposure.
Define Antigen.
Foreign substances having the capacity to
evoke an immunological response
True or False: Types I & IV hypersensitivity are most commonly associated with ocular reactions.
True.
In type 1 hypersensitivity, how long after re-exposure does hypersensitivity reaction occur?
5-30min
*in the initial stage of exposure, activation of cloned B cells occurs in 3-6 days. After re-exposure, hypersensitivity rxn occurs in 5-30minutes.
True or False: Innate Immune Response is the basis for vaccinations.
False. Adaptive Immune Response (which involves antibodies) is the basis for vaccinations.
Give 4 examples of type 4(delayed) hypersensitivity.
- PPD test
- conjunctivitis medicamentosa,
- contact dermatitis,
- chronic graft rejection,
- Type-1 diabetes,
- multiple sclerosis,
- latex
True or False: Type 4 hypersensitivity responds well to antihisaminics.
FALSE!
- Type 4 is NOT responsive to antihistamines
- This is because it is antibody independent. (it is T cell based hypersensitivity)
How long does it take a type 4 hypersensitivity to occur?
2-3 days
True or False: Decongestants are adrenergic agonists.
True
-They cause vasoconstriction.
Why is phenylephrine not commonly used in allergy therapy?
Phenylephrine is not commonly used in allergy therapy due to it’s predilection to produce rebound congestion and, with chronic use, conjunctival medicamentosa
What are the adverse reactions of decongestants?
*General reactions Blur, epithelial erosions, rebound congestion, upper lid retraction *Mydriasis Phenylephrine & Naphazoline *Elevated IOP Naphazoline *Reduced IOP Tetrahydrozoline
What is the only stand alone exception of a topical antihistamine drug?
Emadine (Emadastine)
-Which is a 2nd generation antihistamine.
What are the broader opthalmic indications of antihstamines?
- Allergic conjunctivitis (mild - moderate)
- Myokymia (unilateral spasm of eyelids)
- Allergic rhinitis (sinus)
- Intra-operative anti-miotic
True or False: Dry eyes is one of the adverse reactions of Emedastine (the only stand alone topical antihistamine)
True
What are the serious adverse reactions of Emedastine?
-Keratitis, corneal infiltrates
What drugs do topical antihistamines + Decongestants interact with?
MAOI, EtOH
Name the contraindications of antihistamines + Decongestants topicals.
- Hypersensitivity (topical > oral)
- CVD, DM
- Narrow anterior chamber angles
- Dry eye
How do mast cell stabilizers work?
They are are believed to block Ca++ influx that stimulates degranulation; this effects not only mast cells but other immune cells.
True or Flase: all antihistamines + decongestants topicals are 1st generation antihistamines and all are pregnancy category c and dosing is 4x a day.
True.
True or False: Mast cell stabilizers halt type-1 hypersensitivity reaction.
True: mast cell stabilizers halt type-1 hypersensitivity reaction.
*Because of this they are usually used as a prophylaxis for allergy season.
True or False: nedocromil is the fastest acting topical mast cell stabilizer in chronic care.
True
nesocromil (brand name Arocril) by allergan is the fastest acting topical mast cell stabilizer. And dosing is only 2x a day vs 4x a day of the others.
*it is also fairly safe compared to the other MCSs.
True or False: MCS (mast cell stabilizers) are less likely to cause contact dematitis.
True.
True or False: Mast cell stabilizers almost always cause burning/stinging as one of their adverse reactions.
True. Burning or stinging is a very common adverse reaction of MCS.
Which drug is the only OTC topical antihistamine + MCSs combo?
Ketotifen (brand name: Zaditor) *available OTC as Claritin Eye, Refresh, Alaway
is the only OTC topical antihistamine + MCS combo.
Upper respiratory infection is an adverse reaction associated with which antihistamine + MCS combo?
Elestat
When would you use oral vs topical allergy therapy?
Oral therapy are;
- Better for deeper ocular involvement
- Better for moderate → severe eyelid edema & conjunctival chemosis
Which oral antihistamines, 1st generation or 2nd generation are noticeably lipophilic and thus pass through the blood brain barrier?
1st generation oral antihistaminics such as Diphenhydramine (aka benadyryl) are lipophilic and easily cross the BBB. This is what gives them their sedative (drowsy) properties- CNS effects.
What are the drug interactions for 1st generation oral antihistaminics?
Potassium supplements
Codeine & Opioids (cause constipation-additive effect)
Anticholinergics
True or False: Angle closure glaucoma is one of the contraindications of oral antihistaminics.
True Contraindications of antihistaminics include; -Peptic ulcer -Prostatic hypertrophy -Bladder obstruction -Angle closure glaucoma
True or False: 2nd generation antihistaminics are noticeably less lipohilic than 1st gen oral antihistaminics.
True.
Which drug is the most potent 2nd gen oral antihistamine.
Zyrtec
Which 2nd gen oral antihistamine has least CNS effect?
Allegra
True or False: Lotemax (seroid drug) is safe for long term therapy of SAC (Seasonal Allergic Conjunctivitis) & VKC (vernal keratoconjunctivitis).
True.
