Clay Radke, Professor of Chemical Engineering and Vision Science at University of California, Berkeley (lab page here) will be delivering a seminar, Topical Ophthalmic Drug Delivery on September 23rd, 2013 at 4:00pm in the John A. Moran Eye Center auditorium.
Despite considerable inefficiency, topical ophthalmic drug delivery remains the main application modality to the human eye. We present a new description of tear dynamics that quantifies tear salinity and drug bioavailability by topical administration. The tear supply/drainage system is divided into 5 compartments: upper and lower menisci, upper and lower conjunctival sacs, and tear film. Transient description is provided for each compartment for tear, salinity, and drug. Compartments are coupled to each other and to drug pharmacokinetics (PK) through kinetic routes. Salinity must be accounted for in PK models because osmotic flow is drawn from the cornea/conjunctiva into tear thus diluting the drug. Osmotic water flow through the cornea and conjunctiva contribute 20 to 50 % to the total tear supply. Tear salinity is also critical to dry eye. Predicted tear osmolarity, volume, and tear turnover rates all match available clinical measurements. Drug bioavailability is surprisingly independent of supplied drop volume and viscosity. In spite of this, 30 to 90% of drug is lost to drainage through the punctum depending on specific drug transport and reactive properties. Order of addition of mixed drugs is also found important.