Principles of Ocular Drug adminstration

Question 1

Ocular drugs are used for?

Answer 1

• examination
• dx
• tx

Question 2

Medical Hx considerations

Answer 2

• Drug interactions (MOA or tricylcic antidepressants)
• Allergy/ drug sensitivity
• Family Hx (POAG)
• Renal/Hepatic disease (drug metabolism)
• Respiratory conditions (Beta blockers)
• DM (steroid exacerbate DM)
• Pregnancy

Question 3

Considerations: Fam Hx POAG

Answer 3

Topical steroid may increase IOP

Question 4

Considerations: Cardiovascular disease

Answer 4

• Hypertension - Adrenergic agonists (phenylephedrine - increase/upregulates)
• Congestive Heart disease/Bradycardia (AV block - beta blockers)

Question 5

Considerations: MOA or Tricyclic anti-depressants

Answer 5

Combined with phenylephedrine may lead to cardiovascular effect

Question 6

Considerations: Respiratory disorders

Answer 6

• Beta blockers - broncho-constriction

Question 7

Considerations: DM

Answer 7

• systemic steroids worsen DM

- poor pupil dilation

Question 8

Considerations: Pregnancy

Answer 8

• Risk to fetus vs benefit to px
• careful Cat C - latanoprost
• risk to fetus Cat D - tetracycline
• Cat X - def fetal risk - avoid

Question 9

phases of drug administration

Answer 9

• absorption
• distribution
• metabolism
• elimination

Question 10

Compartment

Answer 10

• region of tissue or fluid through which a drug can diffuse and equilibrate
• each compartment is separated by a barrier

Question 11

Barrier

Answer 11

• region of lower permeability or restricted diffusion between compartments

Question 12

Routes of drug kinetics to the eye

Answer 12

• Trans-corneal
• Non-corneal (scleral/Conjunctival)
• Intravitreal (inj)
• Cross blood retinal barrier
• Distribution from bloodstream via blood-aqueous barrier

Question 13

Routes of drug elimination

Answer 13

• via TM, Schlemm’s canal , episcleral vessels(direct outflow)
• from aqueous to bloodstream (uveal vessels - bulk transport) via blood-aqueous barrier
• via blood-retinal barrier (retinal vessels - active transport)
• eliminates from vitreous (sedimentary)

Question 14

Corneal properties

Answer 14

• major functional barrier also major site of absorption
• Epithelium = Lipophilic
• Stroma = Hydrophilic
• for full penetration requires biphasic solubility

Question 15

Drug Kinetics - Fick’s law

Answer 15

• Rate of drug diffusion is proportional to concentration gradient between the compartments on either side of the barrier
• absorption affected by other drugs, preservatives, infection, inflammation & neuronal control

Question 16

Drug Kinetics - 1st order kinetics

Answer 16

most common drug movement, rate of movement is directly proportional to concentration difference across the barrier (dose = high - linear decrease then re-dose req)

Question 17

Zero - order Kinetics

Answer 17

Drug release is constant over time - slow-release (lacrisert)

Question 18

Prodrugs

Answer 18

• Inactive derivative of drug converted to active form after tissue penetration
• drug metabolite is more active at receptor site
• better penetration, less side-effects
• Latanoprost, travoprost, tafluprost
• Valacyclovir (prodrug of acyclovir)

Question 19

Soft drugs

Answer 19

• Compound (analog) that is rapidly transformed by enzymes to inactive form
• fewer side effects
• Loteprednol etabonate (analog of prednisone)

Question 20

Site specific drugs

Answer 20

• intrinsic tissue esterases transform site specific agents into inactive metabolite shortly after entering target tissue
• sometimes interchanged with soft drugs

Question 21

what do we need to know…

Answer 21

• medical conditions (kidney, liver, cardiac, respirotary)
• Other meds (drug interactions)
• Allergies (sulfa)
• Fam History (POAG)
• Ocular Hx (inflammation)