Antihistaminics and Decongestants Flashcards
What is the number 1 site of ocular allergy?
conjunctiva (can also be lids and lashes)
What is innate immunity?
(<12 hours) non-specific acute response (first-line) that lacks immunological memory
what are the key cells associated with innate immunity?
humoral and cell mediated: killer T cells and macrophages
What is adaptive immunity?
(1-2 weeks) occurs after prior exposure to an antigen and has specificity and memory
what are the key cells associated with the adaptive immune response?
humoral and cell mediated: memory B and T cells
what is an antigen?
a foreign/endogenous substance having the capacity to evoke an immunological response
what is hypersensitivity or an allergic reaction?
exaggerated immune responses to an innate or foreign innocuous antigen = allergen (environmental, biological, chemical based)
what are the 2 types of hypersensitivity responses that are most commonly associated with ocular reactions?
types 1 and 4
what is a type 1 hypersensitivity reaction?
IgE based (only one) - activation of mast cells or basophils (allergy)
what are 3 examples of a type 1 response?
atopy, asthma, anaphylaxis
what is a type 2 hypersensitivity reaction?
(antibody mediated or cytotoxic) non-systemic/local IgM or IgG based attack = local inflammation
what are 3 examples of a type 2 response?
graves disease, myasthenia gravis or autoimmune diseases
what is a type 3 hypersensitivity reaction?
(immune complex) circulating or systemic IgM or IgG based immune complexes (originate in circulation but can land locally)
what are 4 examples of a type 3 response?
arthritis, nephritis, vasculitis, lupus
what is a type 4 hypersensitivity reaction?
(delayed type CD4 and/or cell-mediated CD8) T-cell based reactions that lead to macrophage activation and/or cell lysis = inflammation
what are some examples of a type 4 response?
IDDM, MS, RA, contact dermatitis, conjunctivitis medicamentosa
how quickly does a type 1 hypersensitivity reaction occur?
5-30 min
what are the 5 steps of a type 1 hypersensitivity reaction?
- B-cell + antigen
- B-cell + IgE synthesis
- Mast cell/basophil + surface IgE
- Mast cell/basophil + Ag = Ca++ entry
- Degranulation = histamine release
what cell is local - mast cells or basophils?
mast cells are local (at tissue) and basophils are in blood circulating
what 2 things does Ca++ trigger when it enters a mast cell/basophil?
triggers phospholipase A2 and mast cell degranulation = histamine (pre-formed)
what is phospholipase A2 involved in?
inflammatory cascade
how long does it take for a type 4 response?
2-3 days for development (much faster than adaptive immune response)
what triggers a type 4 response?
re-exposure (memory) response = TB testing, MS, chronic transplant rejection
How is type 4 different than types 1-3?
T-cell based (unlike 1-3) and antibody independent
Does a type 4 response use histamine?
no - cytokines are released upon antigen re-exposure and activate macrophages = phagocytic and lytic enzymes
when might you use an antihistamine with a steroid?
if symptoms include itch and other significant ocular allergy signs (redness, chemosis, eyelid edema) –> involves inflammation (PGs) as well as mast cells
Is itch always a sign of ocular allergy?
no - mast cells can degranulate by scratching and histamine is released
what are 5 allergy therapies?
decongestants, antihistamines, mast cell stabilizers, NSAIDS, steroids
would you advise patients with ocular allergies to use a warm or cold compress?
cold compress - constriction of vessels = less redness and leakage (swelling)
what are 4 adrenergic agonists used for decongestants?
phenylephrine, naphazoline, oxymeazoline, tetrahydrozoline
what are the actions of decongestants?
vasoconstriction - reduces hyperemia and edema (palliative therapy)
How can decongestants differentially diagnose episcleritis?
if the decongestant blanches the conjunctiva (makes it white) - the redness was superficial and was episcleritis vs. scleritis
why are naphazoline, oxymetazoline, tetrahydrozoline less likely to induce mydriasis?
lack a saturated benzene ring = predominantly alpha-adrenergic stimulation
when would you use a decongestant?
allergy induced hyperemia and injection
why is phenylephrine not commonly used as a decongestant?
due to its predilection to produce rebound congestion and with chronic use = conjunctival medicamentosa (need to keep using drop to keep eyes white)
what are the dosing conditions for ocular decongestants?
BID to QID
what are some general reactions to decongestants?
blur, epithelial erosions, rebound congestion, upper lid retraction, mydriasis, elevated/reduced IOP
which decongestants could cause mydriasis?
phenylephrine and naphazoline
which decongestant elevates IOP?
naphazoline
which decongestant reduces IOP?
tetrahydrozoline
what are the contraindications for decongestants?
patients with angle closure glaucoma or narrow angles
which histamine receptor is involved in immediate hypersensitivity?
H1
what does the histamine receptor H2 do?
promotes gastric acid production and immune cell activation
what does the histamine receptor H3 do?
pre-synaptic feedback inhibition (similar to alpha2)
what does the histamine receptor H4 do?
immuno-modulation, inflammation, and nociception roles
what type of histamine receptor does the eye have a lot of?
H2
what are some systemic effects of histamine?
promotes vascular permeability, induces vasodilation (hypotension/tachycardia), causes smooth muscle contraction (bronchoconstriction), stimulates sensory nerves (itching, sneezing)
Are antihistaminics antagonists or inverse agonists?
inverse agonists
when would you use an oral decongestant?
deeper ocular involvement = moderate to severe edema and chemosis
what is the typical dosing for antihistaminic’s?
QD, BID, QID
what are 4 broader ophthalmic uses for antihistaminic’s?
allergic conjunctivitis, myokymia, allergic rhinitis, intra-operative anti-miotic use
why can first generation antihistaminic’s cause drowsiness?
they are lipid soluble and can cross the blood brain barrier
what are 2 types of antihistaminic’s/decongestants?
Vasocon-A and Naphcon-A
what are the components of Vasocon-A?
antihistaminic = antazoline phosphate
decongestant = naphazoline HCl
dosing = QID
ages 6 and up
what are the components of Naphcon-A?
Antihistaminic = pheniramine maleate
decongestant = naphazoline HCl
dosing = QID
ages 6 and up
what are some general adverse effects of antihistaminic’s?
mydriasis, anisocoria, medicmentosa, rebound hyperemia, lacrimation/dry eye, irritation, pain, photophobia, IOP fluctuation, vasoconstriction, suppress accommodation, headache
what are some contraindications for antihistaminic’s?
hypersensitivity, MAOI, alcohol, CVD, diabetes, narrow chamber angles
what are mast cell stabilizers? and when are they used?
oral agents that block Ca++ influx to stop degranulation = HALTS type 1 hypersensitivity reaction
what are 2 ocular conditions that need mast cell stabilizers?
vernal keratoconjunctivitis and giant papillary conjunctivitis
what can patients use to prepare for an upcoming allergy season to reduce their chance of allergy reaction?
can take a mast cell stabilizer as a prophylactic therapy
what are 4 topical mast cell stabilizers for chronic use?
permirolast, nedocromil, lodoxamide, cromolyn
which mast cell stabilizer is only BID and the most rapid?
nedocromil (alocril)
what is the mast cell stabilizer that can be used on a 2 year old?
lodoxamide (alomide)
what is the only over the counter acute antihistaminic/MCS combo drug?
alaway (ketoifen) = BID
what are some acute antihistaminic/MCS combos you need an Rx for?
Bepreve (bepotastine), elestat (epinastine), lastacaft (alcaftadine), optivar (azelastine), pataday (olopatadine)
what are the 2 antihistaminic/MCS that are QD instead of BID?
lastacaft and pataday
what are some adverse effects of antihistaminic/MCS combos?
sting/burn, FB sensation, dry eye, itch, headache, flu-like syndrome, rhinitis, taste changes
what is a contraindication for antihistaminic/MCS?
known hypersensitivity
what is an example of an NSAID used for allergy therapy?
acular (ketorolac tromethamine) = seasonal allergic conjunctivitis (SAC)
what is an example of a steroid used for allergy therapy?
Lotemax (loteprednol etabonate) = safe for long term therapy of SAC and VKC
what are 4 anti-H2 antihistaminic’s?
Tagamet (cimetidine), pepcid (famotidine), axid (nizatidine), zantac (ranitidine)
what are 2 mildly sedating first generation antihistaminic’s?
brompheniramine and chlorpheniramine
what is a moderate sedating first generation antihistaminic?
clemastine
what are 2 strongly sedating first generation antihistaminic’s?
diphenhydramine (benadryl) and promethazine
what are 4 contraindications for first generation antihistaminic’s?
peptic ulcer, prostatic hypertrophy, bladder obstruction, angle closure glaucoma = anticholinergic effects (stopping rest and digest)
what are 4 examples of second generation antihistaminic’s?
allergra (fexofenadine), claritin (loratadine), clarinex (desloratadine), zyrtec (cetirizine)
which second generation antihistaminic has the least CNS effects?
allergra (fexofenadine)
which second generation antihistaminic is the most potent (and most sedating)?
zyrtec (cetirizine)
what is different about second generation antihistaminic’s from first generation?
have a longer elimination profile (allow for some QD dosing) and are less sedating - may have potential to decrease histamine release
Are mast cell stabilizers more or less effective when combined with antihistaminic’s?
the combo drops are more effective
which antihistaminic/MCS combo has anti-H2 properties?
Elestat (epinastidine)
which antihistaminic/MCS combo can cause folliculosis, upper respiratory tract infection?
Elestat (epinastidine) - suppressed immune system may promote infections
