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

Abstract 

Purpose

To 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.

Methods

Five commercial contact lenses were cycled in lens cases in a PHMB- and an Aldox-containing MPS. Single-cycle soaks (6, 16 or 64h) and multi-cycle soaks (6, 16, 142 and 48h) 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 2mL of a tear mimic fluid.

Results

Lenses that exhibited low uptake in a single cycle (with 3mL of MPS) became saturated within ∼3 cycles. PHMB uptake was highest with non-silicone hydrogel (non-SiHy) and/or ionic lenses (∼70% depletion in 16h). PHMB uptake by non-ionic SiHy lenses was low (<40% depletion in a single 3-mL soak of 64h). Aldox uptake was highest for all SiHy lenses (∼80% depletion in 16h).

Conclusions

PHMB 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 (t_1/2=∼120min) compared to Aldox (t_1/2=∼20min) may partially explain observed higher staining after 2–4h with PHMB products used with some lenses, whereas any clinical effects from Aldox would be expected to manifest soon after insertion.

Keywords: Uptake, Release, Sorption and desorption kinetics, Adsorption, Absorption/partitioning, Equilibrium, Lipophilic, Hydrodynamic, Ionic