Final 30-33 Antiallergy Flashcards
Allergy Immunology: Type 1 Hypersensitivity
IgE mediated or Humoral
- immediate allergic response
- when antigens are reintroduced
- IgE antibodies produced at first exposure to antigen, attach to Mast Cells and Basophils
- makes mast cells more susceptible to rupture when individual is reintroduced to same antigen
Type 1 Hypersenstivity Reactions
- inflammatory mediators are released - histamine, prostaglandins, leukotriences
- histamine activates H1 Receptors on blood vessels = vasodialtion, leakage of fluid, due to increased vascular permeability
- H1 receptors in heart, bronchial smooth muscles, mucous membranes, and blood vessels of eye
- H2 receptors located in GI tract, blood vessels, mast cells, and blood vessels of eye
- commonly occur in hay fever, allergic conjunctivitis, asthma
- *Ocularly, release of histamine is the main mediator in type 1 allergic reactions: itchy, tearing, conj and lid edema, papillary reaction
Type I Hypersensitivity Ocular Rxns:
Seasonal Allergic Conjunctivitis (SAC)
Have Fever - most common ocular allergy
- related to specific pollens - exogenous antigens
- seasonal
Type I Hypersensitivity Ocular Rxns:
Perennial Allergic Conjunctivitis (PAC)
- year round allergic conditions - animal dander, dust, mold, feces
Type I & VI Hypersensitivity Ocular Rxns:
Atopic keratoconjunctivitis (AKC)
- a hypersensitivity state caused by predispositional, constitutional, and hereditary factors (ex: genetic conditions)
- usually family hx or personal hx of allergy - atopic dermatis
- sight threatening – tx: topical dual mast cell stabilizers and anti histamines
Type I & VI Hypersensitivity Ocular Rxns:
Vernal Conjunctivitis or Vernal Keratoconjunctivitis (VKC)
- seasonal disorder - adolescent males, bilateral inflammation
- characterized by formation of large papillae with the appearance of cobblestones on upper tarsal conj.
- Sx: intense itching and thick, ropy discharge
- if cornea affected –> photophobia
- may induce ptosis
- potentially sight threatening
Type I & VI Hypersensitivity Ocular Rxns:
Contact Len papillary Conjunctivitis (CLPC)
- previously GPC
- combo of immune + mechanical mechanicals
- proteins on contact lens +_ inflammatory condition
Type I & VI Hypersensitivity Ocular Rxns:
Contact Dermatitis of the Eyelid
- Allergic = ACD | Irritant = ICD
- eyelid contact dermatitis is an inflammatory reaction involving the eyelid skin – caused by contact with Trigger Substance
Decongestant Agents
actions of adrenergic agonists on alpha-adrenergic receptors, aka sympathomimetics - produce vasoconstriction actions
- conj blood vessels contract within minutes causing eyes to whiten
- **Adrenergic agonists stimulate alpha-adrenergic receptors in arterioles of the conj to produce vasoconstriction
- secondary effect - conc. and dose depend. - potential for mydriasis b/c of alpha adrenergic fx on iris dilator
- conditions which do not respond to use of decongestants within 48 hrs should be re-evaluated for whether a more serious condition exists
Decongestant Pharmacology
Class of Meds called: Imidazole derivatives
- naphazoline, tetrahydrozoline, oxymetazoline
Decongestant Indications
- Relieve redness and discomfort of the eyes caused by minor eye irritation
contraindications – concern with mydriatic strengths and doses
- narrow angle glaucoma
- anatomically narrow angle without glaucoma
Decongestant Warnings/Precautions
- overuse of all agents can cause rebound vasodilation and INCREASE redness of eyes
- mydriatic doses – caution for older patients who may develop pigment floaters
Naphazoline:
Decongestant (alpha-adrenergic agonists) - Imidazole Class
- 0.1% conc is Rx only - lower conc is non-rx
Indications:
- relieve redness of eyes caused by minor eye irritation
Admin and Dosage:
- 1 or 2 drops into the conj sac of affected eye every 3-4 hours, up to 4 times daily
Oxymetazoline:
Decongestant (alpha-adrenergic agonists) - Imidazole Class
Indications:
- relieve redness of eyes caused by minor eye irritation
Admin and Dosage
- adults and children at least 6 yo: 1 to 2 drops every 6 hours
Tetrahydrozoline
Decongestant (alpha-adrenergic agonists) - Imidazole Class
Indication:
- relieve redness and discomfort of the eyes caused by minor eye irritation
- temporary relief of irritation and burning caused by dry eye, or exposure to wind or sun
Admin and Dosage
- 1 or 2 drops into affected eye, MAX 4 Drops a day
Decongestant/ANtihistamine Combo:
Naphazoline and Pheniramine (1st gen)
- combo of product can be used for temporary relief of minor itching and redness symptoms from allergy antigen
- topical antihistamines are potential sensitizers and may produce local sensitivity reaction
- use in caution in those with narrow angles or hx of glaucoma
Brimonidine Tartrate 0.025% (Lumify)
Indication:
- ocular redness (OTC): relief of redness of eye due to minor irritations
Mechanism of Action:
- selective alpha-2 receptor agonist – reduces redness by constricting venule
Dose
- instill one drop in affected eye every 6 to 8 hrs up to 4x daily
Ocular Antihistamines
- second generation antihistamines OR selective histamine H1 receptor antagonists
- selectively block the action of histamine on H1 histamine receptors and DO NOT block other receptors
- exception is pheniramine (1st gen)
- first gen oral antihistamines have a low specificity and block other receptors such as cholinergic receptors
Mast Cell Stabilizer Effect
ability to prevent the release of allergic mediators from mast cell
- selectively block action of histamine on H1 histamine receptor and stabilizes the mast cell preventing release
(dual antihistamine/mast cell stabilizers)
Emedastine (Emadine)
- only second generation pure ocular antihistamine
- MoA: selective H1 Receptor antagonist (2nd gen)
- Indications: temp relief of allergic conjunctivitis
- dosage: 1 drop in eye, QID
ADE: Headache, burning or stinging on instillation
Caution: Contact Lens Caution
Ocular Antihistamine: Pharmacology/Usage
use alone or in combine ation of decongestant
- relief of symptoms of allergic conjunctivitis
Ocular Antihistamine:
Warning/Precautions
minimal systemic side fx due to localized site of action - ocular side fx
- use of non-rx agents within same pharmacological classes can be additive
Mast Cell Stabilizers
MoA:
- stabilize mast cells by inhibiting the degranulation of sensitized mast cells after exposure to specific antigens
- drugs have no intrinsic vasoconstrictor, antihistaminic or anti-inflammatory activity
Indications
- Pure Mast Cell stabilizers are used for vernal keratoconjunctivitis and season conjunctivitis
General Pharmacology: Mast Cell Stabilizers
- Nedocromil has fast onset of action than other mast cell stabilizers
- symptom relief may occur within 15 min after instillation
- Perimolast can provide symptomatic relief within days of commencing administration, full effects may require several weeks of therapy
