bns 200 drugs and the eye

8/2/2019 BNS 200 Drugs and the Eye

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Drugs and the eye

By Amos Massele


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Introduction

The eye is the window of the soul

The eyes are undoubtedly the most sensitiveand delicate organs we possess, and perhaps

the most amazing They present us with the window through which

we view the world,

and are responsible for four fifths(80%) of all the

information our brain receives which is probably why we rely on our eyesight

more than any other sense


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some eye disorders


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The eye works like a Camera


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Innervations of the eye

Parasympathetic

Sympathetic


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Eye parts of pharmacologicalinterest

The ciliary body is composed of ciliary muscles& ciliary process

The ciliary bodyserves 2 functions- Secretion of aqueous humor

- Accomodation- Parasympathetic stimulation contracts the ciliary

muscles allowing the lens become convexfocusing on near objects and vice versa

- Contraction of ciliary muscles also widens thespaces in trabecular meshwork loweringintaocular pressure in Glaucoma


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Important general pharmacokinetics of intraoculardrug administration

Most drugs are delivered as drops in aqueous solution

Formulations which prolong contact time include gels,ointments, solid inserts,soft contact lenses,collagenshields etc

Drug penetration into the eye is approx. linearly relatedto the concentration of the drug

Nasolacrymal drainage plays a key role in the systemicabsorption of drugs administered to the eye

Drugs administered by this route bypass the liver andavoid first pass effect". Ocular drugs like Betaadrenergic antagonist(


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I: Drugs used to dilate the pupil(mydriatics)

Mydriasis (pupilary dilatation)

required to examine the retina (fundoscopy)

Two major groups of drugs are used to dilate

the pupil are:(A)anticholinergics(Muscarinic

antagonists/parasympatholytics) eg.tropicamide(eye drops) short acting , facilitate retinal

examination(B) Sympathomimetics like adrenaline and

phenylephrine EYE DROPS


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Cyclopentolate and atropine(anticholinergics)eye drops are preferredfor producing cycloplegia(paralysis of the

cilliary muscle)

Refer to table 1& 2 below


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Table 2:Drugs commonly used to dilate the pupil

Drug receptor(I) Anticholinergics All are antagonists at M3 receptor, on ciliary

muscle- Tropicamide may induce blurred vision,sytemic

absorption may occur- Cyclopentolate -do-- Atropine - do-

(II)Sympathomimetics ---- all are agonist at 1 onradial muscle of iris

- Adrenaline one or two drops 1% soln.

- Phenylephrine one or two drops 10% soln. systemic absorption +

- Dipivefrin one or two drops 0.3 % soln. read more on this


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Table 1: receptors

Tissue - adrenergic receptor - response Iris radial muscle 1 mydriasis Iris sphincter muscle - -

Ciliary epithelium 2/2 aqeous humour production Ciliary muscle 2 relaxation Lacrimal gland 1 secretion

-do- Cholinergic receptor -do- Iris radial muscle - -

Iris sphincter muscle M3 Miosis

Ciliary epithelium - -

Ciliary muscle M3 accommodation

Lacrimal gland M2/M3 secretion


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Nursing implications

Instruct client who has received amydriatic to wear dark sunglasses untilclear vision resumes

Teach the client proper instillation


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2.0 Drugs used to constrict the pupil

(miotics)

Actions: exert a parasympathetic response(stimulate the parasympathetic NS)resulting in:

constriction of the pupil

Contraction of the accommodation muscle

Decrease resistance to outflow of aqeuoushumour


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Drugs to treat glaucoma- drugs whichconstrict the pupil

Aqueous humor(AH) is produced at arate of 2-2.5L/min & flows from posteriorchamber

Then flows via the trabecular meshworkinto canal of Shlemm and eventually intoepiscleral venous plexus and eventuallyinto systemic circulation

Fluid can also flow via the ciliary musclesinto suprachoroid space


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Therapeutic outcomes of miotics

Decrease intraocular pressure

Increase outflow of aqueous humour

Of benefit in the treatment of open angleglaucoma


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Nursing implications of caring for a patient on miotics

Administer at bed time to decrease blurredvision

Avoid in conjuctivitis

Teach client how to administer

Common miotic drugs include Pilocarpine

and Carbachol


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3 : other drugs used to treatglaucoma

Mannitol:

Osmotic diuretic

Used in emergency before surgery

Given IV infusion Shifts water from intracellular & transcellular

compartments (including the eye) into theplasma

Promotes fluid loss by its diuretic action on thekidney

Its major Adverse effect is dehydration


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Carbonic anhydrase inhibitors

Acetazolamide

Useful in acute & chronic glaucoma

A competitive inhibitor of Carbonic anhydrase(CA) enzyme

CA converts CO2 & H20 into H2CO3

Inhibition of this enzyme in the eye reducesaqueous humor production

Revise your notes on diuretics


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Acetazolamide----

Adverse effects include:- nausea,vomiting,loss of taste- Paraesthesia- Metabolic acidosis- Polyuria due to mild diuretic effect

Pharmacokinetics:- Well absorbed orally- Low plasma binding- Half life is 8h eliminated by renal- A slow release preparation is available for twice daily dosing

- Acetazolamide is contraindicated in renal failure,renal stones &in pregnancy


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Topical agents used in glaucoma

Dorzolamide

Is a sulphonamide derivative

Acts as a topical CA inhibitor

May be used alone or as adjunct to a -antagonistlike timolol

May show systemic absorption with rashes,

Adverse effects include local irritation to the eyewith burning sensation,visual blurring etc


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Latanoprost Is a PGF2 analogue Latanoprost can be used in patients who

are intolerant to antagonists like timolol

It lowers intraocular pressure byincreasing uveoscleral outflow


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Selective 2 agonists

Brimonidin:

Is recently introduced for the treatment ofchronic open-angle glaucoma when otherdrugs do not respond adequately

Is used alone or as an adjunct with blocker like timolol

It decreases AH by increasing uveoscleraloutflow


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Selective 2 agonist ---------

Apraclonidine:

Is a derivative of clonidine

Is another selective Selective 2 agonist If formulated for ophthalmic use


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Nursing implications

Carbonic anhydrase inhibitors and osmoticdiuretics like mannitol are diuretics and willincrease urine output

Monitor electrolytes and advise patient totake early in the morning

Beta blockers like timolol ,monitor heartrate

Teach client how to administer


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5:Drugs for eye infections

Antibacterial agents are formulated forophthalmic use see table below:

Drug broad spectrum antibiotics. Chloramphenicol Fluoroquinolones(Eg.Ciprofloxacin) Framycetin sulphate

Aminoglycoside Appropriate antibiotic will depend on C/S of theeye discharge


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Drugs and eye infections------

Please note that:

Acute bacterial conjunctivitis is usuallycaused by Staphylococcal aureus orstreptococcus

All below drug may be applied as eyedrops against

(ie.Chloramphenicol,gentamicin,fusidicacid or fluoroquinolnoes(ciprofloxacin).


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VI:Drugs and inflammatory disorders ofthe eye

Corticosteroids

Topical use must be given under specialist supervision

Should never be used to treat undiagnosed red eyewhich could be due to herpes infection which aggravates

the condition and even lead to blindness. In glaucoma steroids exacerbate glaucoma

Thus steroids require expertise in their use against eyedisorders

Preparations available include: hydrocortisone orbetamethasone eye drops/ointment


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6 :Drugs for inflammatory disorders of the eye

Antihistamines& Mast cell stabilizers:

These are used to treat allergic orseasonal conjunctivitis

Topical antihistamine preparations forophthalmic use include:

- Antazoline & levocabastine

- They may cause eye irritation with edemaof eyelids,blurred visison,sytemiceffectsmay occur with drowsiness


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Drugs for inflammatory disorders of the eye

Sodium chromoglycate or nedocromileyedrops are widely used in the long termtreatment of allergic conjuctivitis

Sodium chromogycate is very safecausing only mild stinging as its ADR

Lodoxamide causes itching and

lacrimation and flushing A new drug Olopatidine is another mastcell stabilizer under scrutiny


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7: Local anesthetics for the eye

Amethocaine & Oxybuprocaine are widely usedas topical LA

Proxymetacaine is used in pediatrics as itcauses less stinging

Amethocaine causes profound local anesthesiaand is suitable for minor surgical procedures

Oxybuprocaine lignocaine plus fluorescein is

used intonometry Lignocaineadrenaline is often injected into

the eyelid for minor surgery


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Adverse effects on the eye ofsystemic drug therapy

Stevens-Johnson Syndrome involves up to2/3 of patients

Of these 1/3 may suffer permanent eyedamage see table below for adverseocular effects of drugs


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Some adverse ocular effects of drugs

Drug anatomical site ADR on eye

-Anticholinergics -lacrimal apparatus - dry secretions

-Cholinergic agents

lacrimal apparatus- increase tear

secretion

-Amiodarone,amodiaquine-}- cornea microdeposits- reducedvision

Phenothiazine,gold} -do-


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Corticosteroids - lens- - cataract formation

Anticholinergics lens impared

{ accomodation & blurredvision

Oral contraceptives lens lens hydration

increased blurredvisison


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Anticholinergics use in glaucoma

- Cause increased intraocular pressureleading to reduced visual acuity

- Chloroqine -optic nerve- optic atrophy- Ethambutol -do -do-

- Chloramphenicol - do- -do-

- They above drugs also induce retrobulbarneuritis, optic atrophy may lead topermanent visual loss


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Digoxin - retina - impaired yellow-

green vision

Sildenafril(Viagra) -retina- blue vision

bns 200 drugs and the eye

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