Ocular drug administration

Question 1

What is a drug called when it’s working at receptor level?

Answer 1

Agonist or antagonist

Question 2

What is a drug called when it’s working at enzyme level?

Answer 2

Activator or inhibitor

Question 3

Name the 2 ways in which ocular drugs can be delivered to ocular tissue and give 2 examples for each way.

Answer 3

Locally:
Eye drops
Ointments
Periocular injections
Intraocular injections
Systemically:
Orally
IV

Question 4

What does the rate and absorption of topically instilled drugs depend on? (3)

Answer 4

-Elimination by nasolacrimal drainage
-Time the drug remains in the conjunctival cul-de-sac & precorneal tear film
-Drug binding to tear proteins
-Drug metabolism by tear & tissue proteins
-Rate of diffusion across the cornea & conjunctiva

Question 5

Describe the distribution of ocular drugs. (5)

Answer 5

Trans-corneal absorption»> Accumulation in aqueous humor»>Distribution to intraocular structures»>Trabecular meshwork pathway»> Distribution to systemic circulation

Question 6

Name 2 prodrugs for enhanced ocular permeability.

Answer 6

Dipivefrin hydrochloride
Latanoprost

Question 7

Give 3 examples for each of the following types drug delivery to the eyes:

a) Topical
b) Periocular
c) Intraocular
d) Systemic

Answer 7

Topical- drop, ointment, gel, soft contact lens
Periocular- sub-conjunctival, sub-tenon, peribulbar, retrobulbar
Intraocular- intracameral, intravitreal
Systemic- oral, intravenous, intramuscular

Question 8

Which factors influence local drug penetration into ocular tissue? (4)

Answer 8

1. Drug concentration and solubility:
   higher concentration – better penetration
   e.g pilocarpine 1-4% but limited by reflex tearing
2. Viscosity: addition of methylcellulose and polyvinyl alcohol increases drug penetration by increasing contact time with cornea and altering corneal epithelium
3. Lipid solubility: higher lipid solubility- more penetration
4. Surfactants: preservatives alter cell membrane in cornea and increase drug permeability e.g. benzylkonium and thiomersal
5. pH: the normal tear pH is 7.4
   If drug pH is much different, this will cause reflex tearing
6. Drug tonicity: when an alkaloid drug is put in relatively alkaloid medium, the proportion of the uncharged form will increase, thus more penetration
7. Molecular weight and size