Latanoprost uptake and release from commercial contact lenses
This study investigated the potential of delivering an anti-glaucoma drug using commercial silicone hydrogel (SiHy) contact lenses. The moderately hydrophobic drug latanoprost was rapidly loaded in 4 min by swelling contact lenses in a solution of the drug in n-propanol. A fraction of the drug was radiolabeled, thus allowing measurement of the uptake and subsequent release of drug into artificial tear fluid. Three questions were addressed: (1) how much drug can be loaded into each type of lens, (2) how fast is drug release, and (3) how are these values related to the contact lens chemistry. The results showed that much more latanoprost could be loaded into SiHy lenses than a conventional contact lens of poly(hydroxyethyl methacrylate). The drug uptake correlated with the amount of swelling in n-propanol, with Galyfilcon lenses having the greatest swelling and highest drug uptake. The drug release from the SiHy lenses occurred over days, whereas the conventional lens released nearly all drug in a burst over a few hours. To examine correlations between lens chemistry, drug chemistry and uptake, and solvent chemistry, the Hansen solubility parameters were calculated using estimates of contact lens chemistry. These results showed that drug uptake in SiHy lenses correlated with favorable solubility parameter interactions between the n-propanol and the lens material, but did not correlate with interactions between the drug and the lens materials.