When Treating Eye Infections Drug Considerations When Treating Eye Infections

Considerations Demonstrate application of drug to owner. Choose a drug with an easy route of administration Culture and sensitivity to choose most effective antimicrobial and reduce microbial resistance. If broad spectrum antimicrobial used, uses four quadrant approach.

Four Quadrant Approach to Antimicrobials

Considerations Topical preparations are preferable to systemic. If medication is applied bilaterally where one eye is being treated prophylactically, treat the unaffected eye first to avoid cross contamination during administration.

Considerations There are 3 barriers to the passage of drugs into the eye:Corneal epithelial layer. Blood-aqueous barrier.  Blood-retinal barrier.

Corneal epithelial layer: Non-keratinized stratified squamous epithelium. Excludes hydrophilic polarised drugs, eg aminoglycosides    , unless the cornea is ulcerated when such drugs can pass into the anterior chamber. Rapidly penetrated by lipophilic drugs   →    anterior segment, eg chloramphenicol    , fluoroquinolones  [Therapeutics: nitrofurans nitroimidazoles quinolones]  .

Blood Aqueous Barrier Junctions between cells of the non-pigmented ciliary body epithelium and the iris capillary endothelium.

Blood retinal barrier Intercellular junctions: Vascular endothelium of retinal vessels and choroidal vessels. Retinal pigment epithelium.

Factors determining how well drugs cross these barriers: Lipid solubility. Hydrophilic or polar drugs. Protein binding affinity. Molecular weight. Note: Damage or disease to barriers affects their function- usually increasing the passage of drugs.

Types of drugs available for therapy of the eye Antibiotics : Topical. Subconjunctival. Systemic. Intra-ocular. Antifungals : Subconjunctival (miconazole    ).

Types of drugs available for therapy of the eye Antiviral : Topical only. Anti-inflammatory drugs : Corticosteroids - topical/subconjunctival/systemic. Non-steroidal drugs - topical/systemic. Antihistamines - topical/systemic. DMSO  [Dimethyl sulfoxide]  - topical/systemic.

Types of drugs available for therapy of the eye Autonomic drugs : Parasympathomimetics (miotics) - topical. Parasympatholytics (mydriatics) - topical. Sympathomimetics - topical. Disinfectants : 1% -povidone iodine    solution diluted in saline - topical. Corneal dehydrating agents : 5% hypertonic saline ointment - topical. Artificial tears - topical. Ocular lubricants - topical.