Principles of Ocular Drug adminstration Flashcards
Ocular drugs are used for?
- examination
- dx
- tx
Medical Hx considerations
- 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
Considerations: Fam Hx POAG
Topical steroid may increase IOP
Considerations: Cardiovascular disease
- Hypertension - Adrenergic agonists (phenylephedrine - increase/upregulates)
- Congestive Heart disease/Bradycardia (AV block - beta blockers)
Considerations: MOA or Tricyclic anti-depressants
Combined with phenylephedrine may lead to cardiovascular effect
Considerations: Respiratory disorders
- Beta blockers - broncho-constriction
Considerations: DM
- systemic steroids worsen DM
- poor pupil dilation
Considerations: Pregnancy
- Risk to fetus vs benefit to px
- careful Cat C - latanoprost
- risk to fetus Cat D - tetracycline
- Cat X - def fetal risk - avoid
phases of drug administration
- absorption
- distribution
- metabolism
- elimination
Compartment
- region of tissue or fluid through which a drug can diffuse and equilibrate
- each compartment is separated by a barrier
Barrier
- region of lower permeability or restricted diffusion between compartments
Routes of drug kinetics to the eye
- Trans-corneal
- Non-corneal (scleral/Conjunctival)
- Intravitreal (inj)
- Cross blood retinal barrier
- Distribution from bloodstream via blood-aqueous barrier
Routes of drug elimination
- 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)
Corneal properties
- major functional barrier also major site of absorption
- Epithelium = Lipophilic
- Stroma = Hydrophilic
- for full penetration requires biphasic solubility
Drug Kinetics - Fick’s law
- 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
Drug Kinetics - 1st order kinetics
most common drug movement, rate of movement is directly proportional to concentration difference across the barrier (dose = high - linear decrease then re-dose req)
Zero - order Kinetics
Drug release is constant over time - slow-release (lacrisert)
Prodrugs
- 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)
Soft drugs
- Compound (analog) that is rapidly transformed by enzymes to inactive form
- fewer side effects
- Loteprednol etabonate (analog of prednisone)
Site specific drugs
- intrinsic tissue esterases transform site specific agents into inactive metabolite shortly after entering target tissue
- sometimes interchanged with soft drugs
what do we need to know…
- medical conditions (kidney, liver, cardiac, respirotary)
- Other meds (drug interactions)
- Allergies (sulfa)
- Fam History (POAG)
- Ocular Hx (inflammation)
