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8/13/2019 Pharm.ther. Eye, Ear & Skin
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Pharmacotherapy of the eye,
ear and skin disordersSutomo Tanzil
Department of Pharmacology, Facultyof Medicine, Sriwijaya University
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Fig. 9.2 Rang & Dale pg 124
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Ocular physiology/pharmacology
Vision depends upon the eye converting light falling on theretina into an electrical signal to the brain
The ciliary muscle is a circular smooth muscle attached tothe lens. It has a parasympathetic (PS) nerve supply and
contracts in response to PS stimulation. Muscarinic agonists fix the lens for near vision, while
antimuscarinic drugs fix the lens for far objects with blurringof near vision, a state known as cycloplegia.
Pupil size is determined by 2 smooth muscle layers of theiris. The constrictor muscle is more powerful and receivesparasympathetic innervation. The radial (dilator) muscle issympathetically innervated (1-receptors).
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Ocular physiology/pharmacology
Miosis occurs in response to muscarinic agonists
Mydriasis can occur in response muscarinic antagonists or to1-adrenoceptor agonists.
Miosis also accompanies accommodation for near vision, a
response mediated by the PS nervous system Mydriasis has the effect of moving the iris towards the
cornea and narrowing the anterior angle between the irisand the cornea. This can reduce aqueous humour outflowthrough the canal of Schlemm.
The intraocular pressure rises if drainage of the aqueoushumour is impaired, leading to the occurrence of glaucoma,that may cause prrogressive loss of vision
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Clinical pharmacology of the
cholinomimetics
In the past, glaucoma was treated w/ either direct
agonists (pilocarpine, carbachol) or cholinesterase
inhibitors (physostigmine,echothiophate). For
chronic glaucoma, these drugs have been largelyreplaced by topical beta-blockers and prostaglandin
derivatives.
Acute angle-closure glaucoma is a medical
emergency that is frequently treated initially w/drugs but usually requires surgery for permanent
correction (iridectomy).
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Drugs used for chronic th/of simple
(open-angle) glaucoma
Reducing aqueous humour production : BB(betaxolol, timolol); 2-agonists(brimonidine, dipivefrine); carbonic
anhydrase inhibitors ( acetazolamide,brinzolamide, dorzolamide).
Increasing aqueous humour outflow : Pgderivatives ( latanoprost, travoprost);
2
-agonists (brimonidine, dipivefrine);muscarinic agonists (pilocarpine).
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Mechanisms of action of drugs used in
open-angle glaucoma
Cholinomimetics(eg.pilocarpin): ciliary musclecontraction, opening of trabecular meshwork;increased outflow
-agonists (eg.dipivefrine) : increased outflow
2-agonists (eg.brimonidine): decreased aqueoussecretion
Beta-blockers (eg.timolol, betaxolol) : decreased
aqueous secretion from ciliary epithelium Diuretics(eg.acetazolamide) : decreased aqueous
secretion due to lack of bicarbonate ions.
Prostaglandins (eg.latanoprost, travoprost):
increased outflow
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The clinical pharmacology of
antimuscarinics
Atropine, homatropine, cyclopentolate, tropicamide
Antimuscarinics should never be used for mydriasisunless cycloplegia or prolonged action is required.
1-agonists, eg. phenylephrine, produce a short-lasting mydriasis that is usually sufficient forfunduscopic examination.
It is also used to prevent synechia (adhesion)
formation in uveitis and iritis. The longer-lastingpreparation, such as homatropine, are valuable forthis indication.
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Carbonic anhydrase inhibitors
Acetazolamide (oral), brinzolamide (eyedrops), dorzolamide (eye drops)
Inhibition of carbonic anhydrase results in
reduced formation of aqueous humour Used in the th/of glaucoma in patients who
are BB resistant or in whom a BB iscontraindicated
Acetazolamide is a sulfonamide derivative,therefore, do not use it in people w/ a historyof severe allergy to sulfonamide
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Other topical applications for the eye
Antibacterials : gentamicin, chloramphenicol, fusidicacid, neomycin & chlortetracycline
Antivirals : acyclovir
Corticosteroids : dexamethasone. Prolonged use can
lead to thinning of the sclera or cornea, or formationof a steroid cataract
Antiallergics : antazoline
Local anaesthetics : lidocaine/oxybuprocaine for
tonometry, removal of cataracts. NSAIDs : diclofenac, flurbiprofen & ketorolac
Artificial tears : hydroxypropyl methylcellulose,carbomers
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ARMD (age-related macular degeneration)
Dry (non-exudative) form : 85-90% of cases
Wet (exudative) form produces severe loss ofvision in 70% of eyes within 2 years
Th/:high-dose of anti-oxidants, laserphotocoagulation of neovascular tissue,photodynamic th/ using photosensitizing
agent verteportin, intravitreal injection ofbevacizumab/ranibizumab (vascular growthfactor inhibitors)
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Vertigo
Hallucination of motion, usually perceived as
spinning, which is generated in the vestibular
system of the inner ear
Caused by Menieres disease, benign positionalvertigo, migraine, vestibular neuronitis, multiple
sclerosis, brainstem ischaemia, temporol lobe
epilepsy, cerebellopontine angle tumours
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Neurochemistry of vertigo
Glutamate (excitatory via NMDA )
Acetylcholine (excitatory via M2)
GABA (inhibitory via GABAA& GABAB) Histamine (excitatory via H1& H2)
NA (modulation of vestibular sensory
transmission) Dopamine (excitatory)
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Drugs for TH/ of Vertigo
Antihistamine (cyclizine, promethazine, most
widely used)
Antimuscarinic (hyoscine)
Benzodiazepine (short-term for severe vertigo)
Cimetidine.
H-receptor agonist (betahistine)
D-receptor antagonist (prochlorprazine)
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Management of vertigo
Acute vertigo (vest.neuronitis) : antiemetic agents
Benign parox.vertigo : less responds to drugs,effectively treated w/ vestibular exercises
Menieres disease : promethazine, cinnarizine or
prochlorprazine. Furosemide & HCT can beattempted for persistent synptoms.
Betahistine is often co-prescribed w/ a diuretic.
For refractory symptoms, vestibular apparatus can
be ablated w/ local delivery of gentamicin , or w/surgical treatment.
AHs , vasodilators and antiparkinsonians can causevertigo.
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