OCULAR PHarm for medical students and bds

OCULAR PHarm for medical students and bds

1. Ocular Pharmacology

2. Routes of
Administration

3. Overview
delivery methods - eye drops, ointments,
injections
•drug classifications

4. Eye drops
most ocular medications are delivered
topically - maximizes anterior segment
concentrations and minimizes systemic
toxicity
•drug gradient from tear reservoir to corneal
and conjunctival epithelium forces passive
absorption

5. Eye drops
Factors affecting absorption:
–drug concentration (limited by tonicity) and
solubility (aqueous solution v’s suspension)
–viscosity (increased residence time)

6. Eye drops
lipid solubility: lipid rich epithelial cell membrane
v’s water rich stroma
–pH and ionic charge - most eye drops are weak
bases existing in both charged and uncharged
forms enhancing absorption

7. Eye drops
Surfactants - preservatives used are surface-
active agents that alter cell membranes in the
cornea as well as bacteria, increasing drug
permeability and preventing bacterial
contamination

8. Eye drops
Reflex tearing: ocular irritation and secondary
tearing wash out of the drug reservoir in the tears
and reduce contact time with cornea. This occurs
when drops are not isotonic, have non-
physiological pH or contain irritants

9. Eye drops
Tissue binding: proteins in the tears and on
the ocular surface may bind drug making the
drug unavailable or creating a slow release
reservoir. This may affect peak effect and
duration of action as well as delayed local
toxicity eg. ongoing toxic retinal effects of
hydroxychloroquine even after
discontinuation

10. Eye ointments
increases contact time of drug with ocular
surface
•mixture of petrolatum and mineral oil
•water-soluble drugs are insolvent in the
ointment and are present as microcrystals.
The surface microcrystals dissolve in the
tears, the rest are trapped until the ointment
melts

11. Eye ointments
only drugs with high lipid solubility and some
water solubility will get into both tears and
corneal epithelium eg. chloramphenicol and
tetracycline both achieve higher aqueous
levels as ointment rather than drops

12. Peri-ocular injections
subconjunctival, subTenon’s and retrobulbar
•allow drugs to bypass the
conjunctival/corneal epithelial barrier and
reach therapeutic levels in the posterior
segment
•eg: anaesthetic agents, steroids, botulinum
toxin

13. Intraocular injections
allow instant drug delivery at therapeutic
concentrations to target site
•intracameral eg. antibiotics, viscoelastics,
miochol
•intravitreal eg. triamcinolone, avastin

14. Systemic
drug getting into eye from systemic circulation
limited by tight junctions in vascular
endothelium of retinal vessels, and non-
pigmented epithelium of ciliary body
•drugs with higher lipid solubility pass through
blood-ocular barrier more readily

15. Systemic
extent of drug bound to plasma proteins also
effects access of drug into eye - only
unbound form can pass blood-ocular barrier
–bolus administration exceeds the capacity of a
drug to bind to plasma proteins and so leads to
higher intraocular drug levels than with slow IV
drip

16. Sustained release devices
devices available for steroid, gancyclovir
delivery within vitreous cavity

17. Classes of Drugs

18. Cholinergics
Muscarinic
•Nicotinic

19. Adrenergic agents
direct acting eg.phenylephrine
•indirect acting eg. brimonidine
•agonists eg dipivefrin

20. Beta-blockers
important to be aware of side effect profile
before administering

21. Carbonic anhydrase
inhibitors
dorzolamide, brinzolamide, acetazolamide

22. Osmotic agents
glycerol, mannitol

23. NSAIDs
topical, oral

24. Steroids
prevent or suppress local hyperthermia,
vascular congestion, oedema, pain of
inflammatory responses.... and late
inflammatory responses such as capillary
and fibroblast proliferation, collagen
deposition and scarring

25. Antivirals
acyclovir, gancyclovir, foscarnet

26. Local anaesthetics
oxybuprocain, alacaine, tetracaine
•lignocaine, bupivacaine

27. so many.....
pick one drug per week and learn its
indications, contraindications, actions,
side effects

28. Thank you!