OCULAR PHarm for medical students and bds
- 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
- 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
- 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
- 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!