Ocular pharmacology

Section 1
Pharmacologic principles
Especial forms and administrations
routes of eye drugs
Section 2
Ocular pharmacotherapeutics
Current and common drug groups
Pharmacokinetics
To achieve a therapeutic effect , a drug must
reach it's site of action in sufficient
concentration :
• Amount administered
• Extent & rate of absorption at the
administration site
• Distribution & binding in tissues
• Movement by bulk flow in circulating
fluids
• Transport between compartments
• Biotransformation
• Excretion
Eye drops
• Most ocular medications
• Adequate concentration in anterior
segment
• Without incurring unwanted effects in
other systems
Eye drops
Some features limit its effectiveness :
* Very little of an administered drop
When a 50 µl eye drop is delivered , the
volume of lachrymal fluid rises about 10 µl
in the blinking eye of an upright patient.
(20% of administered drug is retained )
* Rapid turnover of fluid , 16% per minute ,
and much more if the drop elicits reflex
tearing
Eye drop
Some measures improve ocular absorption:
• More than one eye drop → wait 5minutes
between drops
• Compress the nasolachrymal duct to prevent
egress of tears and to reduce systemic
absorption through the nasal mucosa
Eye drop
• Contact time of eye drop medication is short ,
• The rate of transfer from the tear fluid into the
cornea is critical .
• Corneal epitheliuum and endothelium have tight
intercellular junctions
• Drug concentration
• Solubility
• Viscosity
• Reflex tearing
Solubility
To traverse the cornea , a drug must pass in
turn through :
• Lipid rich environment of the epithelial cell
membrane
• Water rich environment of the stroma
• Lipid barrier at the endothelium
Reflex tearing
• Reduces the contact time of the drug with
the cornea
• Any physical contact that elicit blinking
reflex
• PH value very different from 7.4
Ointments
• Increasing the contact time of ocular
medications
• Consist of petrolatum and mineral oil
• Melt at body temperature
Periocualr injections
• Sub conjunctiva
• Sub tenon
• Retrobulbar
• Peribulbar
Intraocualr injections

• Intracameral
• Intravitreal
Systemic therapy
• Blood ocular barriers limit access through
vascular channels
• More readily penetrated by drugs with
higher lipid solubilities
• The unbound to plasma proteins drugs
can cross the blood ocular barriers
Cholinergic agents
• Affect the activity acetylcholine
receptors in synaps of the peripheral
nervous system
• parasympatetic effectors sites are in
the iris sphincter and ciliary body
Cholinergic agents
• Direct acting agonists act on the receptor
to elicit an excitatory postsynaptic
potential
• Indirect acting agonists inhibit the
acetylcholine esterase of the synaptic cleft
, preventing deactivation of endogenous
acetylcholine
• Antagonists block the action of
acetylcholine on the receptors
Cholinergic agents
• Parasympathomimetic agents :
• Contraction of the iris sphincter (miosis)
and changes the anatomical relationship
of the iris to the lens and chamber angle
• Contraction of the circular fibers of the
cilliary muscle ( accommodation)
• Contraction of the longitudinal fibers of
the cilliary muscle ( outflow facility ↑)
Parasympathomimetic
agents
• Miosis → narrow angle glaucoma
• Accommodation → accommodative
esotropia
• increasing outflow facility → open angle
glaucoma
accommodative esotropia
• The near response is a synkinetic of
accommodation , miosis and convergence
• Parasympathomimetic agents reduce the
need to accommodate , the patient not
only experience lees accommodation but
also less convergence
Parasympathomimetic
agents
• Acetylcholine ( miochol ) → intracameral
• Carbacol ( more effective and longer
lasting ) → intracameral
• Pilocarpine 0.12% confirm Adie tonic pupil
″ 1- 6% in the treatment
of glaucoma
Parasympathomimetic agents

Side effects :

• Miosis
• Induced myopia and accommodation
• Cataractogenesis
• Retinal tear or even rhegmatogenous
detachment
Parasympathomimetic
agents
Indirect agonist such as echothiophate
( phospholine iodide )
• Longer duration of action
• Frequently more potent
• Twice daily treatment is sufficient
Parasympathomimetic
antagonist
• Paralysis of the iris sphincter → mydriasis
→ facilitating fundus examination ,
preventing posterior synechia
• Paralyze the ciliary muscle → inhibit
accommodation , relieve pain associated
with iridocyclitis , accurate refraction
Parasympathomimetic
antagonist

• Atropine 7- 14 days lasting

7-
• Homatropine 3 days
• Cyclopentolate 1-
1- 2 days
• Tropicamide 4- 6hours
4-
Parasympathomimetic
antagonist
Side effects :
• Ocular
Ocular→
→ due to midriasis
• Systemic → dose related toxicity
Flashing , fever , tachycardia , ……
 Adrenergic receptors
• α1 mediate smooth muscle contraction
• α2 mediate feedback inhibition of
presynaptic sympathetic
• β1 predominantly in the heart
• β2 mediate relaxation of smooth
muscle in most blood vessels and in the
bronchi
α1 adrenergic agonist
• Stimulation of the iris dilator muscle
⇒ mydriasis
• Systemic absorption may elevate
systemic blood pressure
• Such as phenylephrine
α2 adrenergic agonist
• prevents release of norepinephrine at
nerve terminals
• Decrease aqueous production as well as
episcleral venous pressure & improves
trabecular outflow
• Such as apraclonidine hydrochloride
α1 adrenergic antagonist
• Inhibit adrenergic tone to the dilator
muscle ⇒ miosis
• Differentiating angle closure glaucoma
from POAG
• Such as thymoxamine
β2 adrenergic agonist
• Lower IOP by increasing uveoscleral
outflow and perhaps through the
trabecular meshwork
• L- epinephrine (α
(α, β agonist)
• Side effects : black deposits in the
conjunctiva
Reversible cystoid maculopathy ( 25% of
aphakic eyes )
β adrenergic antagonist
β blocker
• Lower IOP by reducing aqueous humor
production as much as 50%
• Timolol maleate ( timoptic ) and
levobunolol ( betagan ) are mixed β1 ,β2
antagonists
β1 adrenergic antagonist
• Significantly safer when pulmonary ,
cardiac , CNS or other systemic conditions
are considered
• Such as Betaxolol ( a selective drug )
Carbonic anhydrase inhibitor
• Mechanisms of aqueous secretion are not
fully understood
• Decrease of aqueous secretion depend
active transport Na by Na+ ,K+ , ATP ase on
the surface of nonpigmented epithelial
cells
_
• +
Na transport partially linked to Hco3
formation
_
• Hco3 formation reduced by inhibition of
the enzyme carbonic anhydrase
 CAIs drugs
• Systemic : Acetazolamide
( diamox ) 250-
250- 500mg 4 - 6h
duration of action
Methazolamide
• Topical : Dorzolamide ( trusopt )
Brinzolamide ( azopt)
Treatment of all glaucomas
CAIs drugs side effects
• Metabolic acidosis
• Urinary tract stone formation
• Numbness and tingling of the hands ,
feet and lips
• Malaise
• Anorexia and weight loss , nausea
• Depression
Prostaglandin analogs
• New class of ocular hypertensive agents
• Latanoprost ( Xalatan)
Lower IOP by enhancing uveoscleral outflow
– reduce the pressure ( 25-
25- 35% )
Once daily dosing
Lack of cardiopulmonary effects
Ocular side effects : darkening of the iris
and periocular skin , cystoid macular
edema , uveitis
Osmotic agents
• Reduce IOP and vitreous volume by
drawing fluid out of the eye across
vascular barriers
• Used in the short management of acute
glaucoma and prior to cataract surgery
• Used with care in cardiovascular disorders:
CHF , hypertension , recent MI
 Anti inflammatory agents
• glucocorticoids
• Non Steroidal Anti-
Anti-Inflammatory Agents
( NSAIDs )
• Antihistamine
• Histamine release blocker
• Anti fibrotics
 Glucocorticoids

• Prevent or suppress corneal graft

rejection
Anterior chamber reaction
Immune or traumatic
uveitis Severe ocular
inflammation:
Subconj, retrobulbar , systemic
Glucocorticoids
Adverse effects of
glucocorticoids
• Glaucoma
• Post subcapsualr cataract
• Exacerbation of bacterial and
viral infection
• Ptosis , mydriasis , scleral
melting
• Suppression of the pituitary
adrenal axis
• Gluconeogenesis
• Peptic ulcer
NSAIDs
• Salicylates : aspirin , mefenamic acid
• Indoles : indomethacin
• Phenyl alkanoic acid : diclofenac ,
ibuperofen , naproxen
• Pyrazolones : phenylbutazone
Mast cell stabilizer &
antihistamine
• Allergic conjunctivitis : an immediate
hypersensivity reaction ( IgE)
• Released histamine : capillary
dilation & increased permeability →
injection & swelling
• Topical antihistamine : antazoline →
mild allergic symptoms
Cromolyn sodium

• Blocker of histamine release

• The therapy of choice for severe
vernal & atopic conjunctivitis
Anti proliferative agents
• In the treatment of severe ocular
inflammatory diseases :
Behjet syndrome
sympathetic ophthalmia

• Fluorouracil – mitomycine C
Antibiotic therapy
• Drug penetration in cornea
• Blood ocular barriers
• Select effective antibiotics
• Gram stain , culture and antibiogram
• Immediate intravitreal injection of
broad spectrum antibiotics in severe
endophthalmitis
Antibacterial agents
• Penicillin's
• Cephalosporine
• Sulfonamids
• Tetracyclin
• Chloramphenicol
• Aminoglycosids
• Fluoroquinolonbs
Antifungal
• Polyenes : natamycine 5% suspension for
topical ophthalmic use
• Amphotericine B at .25% - 0.5% in sterile
water
• These agents penetrate the cornea poorly
• Active topically against a variety of
filamentous fungi : aspergillus ,
cephalosporium, fusarium , penicillium ,
yeast candida albicans
Antifungal
• Imidazols : miconazole 1% solution
subconjunctivally or topically
• Miconazole penetrate the cornea
poorly
• Ketoconazole 200 mg tablet
( every 6-
6- 8h)
• Penetrates the blood – ocular barrier
poorly but therapeutic levels can be
achieved in inflamed eyes
• Aspergillus , coccidioides ,
cryptococus & candida
Antifungal
• Flucytosine: orally at 50 -150 mg/kg daily
divided into four doses
• Penetrates the blood ocular barrier well
• Use primarily as an adjunct to systemic
amphotericin B therapy
Antiviral agents
• Topical :
idoxuridine
trifluridine ( TFT)
vidarabine
Antiviral agents
• Systemic :
Acyclovir → herpes zoster,
prevent of HSV kratitis
Can be used topically , orally or
intravenously
Medication for
acanthamoeba infection
• A corneal pathogen → contact lens
users
• No single drug is effective in treating
all acanthamoeba keratitis
• Polyhexamethylene biguanid
( 0.02% solution ) first line agent
• Chlorhexidine , neomycine
,polymyxin, B gramicidine
mixtures , natamycine 5%
Anesthetics agents
• Topical : for tonometery , gonioscopy
, removal of superficial Fb ,
corneal scraping , laser procedures
• Local : retrobubar and eyelid blocks
→ excellent anesthesia for surgery
Anesthetics agents

• Esters : proparacaine , tetracaine

• Amides : lidocaine 40 – 60 min
bupivacain ( marcaine ) long
acting several hours