Lipophilic versus hydrodynamic modes of uptake and release by contact lenses of active entities used in multipurpose solutions

PurposeTo determine if the silicone-type components of new high Dk lens materials contribute significantly to uptake and/or release of two common antimicrobial agents, myristamidopropyl dimethylamine (Aldox) and poly[hexamethylene biguanide hydrochloride] (PHMB), found in multipurpose solutions.MethodsFive commercial contact lenses were cycled in lens cases in a PHMB- and an Aldox-containing MPS. Single-cycle soaks (6, 16 or 64 h) and multi-cycle soaks (6, 16, 142 and 48 h) were used to assess kinetics and saturation effects of uptake. Lens capacity for uptake of each entity was determined using a semi-saturation model. Release kinetics was assessed for these semi-saturated lenses (100-mL MPS-soaked) in 2 mL of a tear mimic fluid.ResultsLenses that exhibited low uptake in a single cycle (with 3 mL of MPS) became saturated within ∼3 cycles. PHMB uptake was highest with non-silicone hydrogel (non-SiHy) and/or ionic lenses (∼70% depletion in 16 h). PHMB uptake by non-ionic SiHy lenses was low (<40% depletion in a single 3-mL soak of 64 h). Aldox uptake was highest for all SiHy lenses (∼80% depletion in 16 h).ConclusionsPHMB uptake capacity was highest by ionic and non-SiHy lenses, while Aldox uptake capacity was much higher with all SiHy lenses than with any non-SiHy lens. The slower desorption of PHMB (t1/2 = ∼120 min) compared to Aldox (t1/2 = ∼20 min) may partially explain observed higher staining after 2–4 h with PHMB products used with some lenses, whereas any clinical effects from Aldox would be expected to manifest soon after insertion.