title: Lipophilic versus hydrodynamic modes of uptake and release by contact lenses of active entities used in multipurpose solutions.
abstract: OBJECTIVE
  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 approximately 3 cycles. PHMB uptake was highest with non-silicone hydrogel (non-SiHy) and/or ionic lenses (approximately 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 (approximately 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)= approximately 120min) compared to Aldox (t(1/2)= approximately 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.
authors.affiliation: Advanced Medical Optics, Inc., Santa Ana, CA 92705, USA. hayes.powell@amo-inc.com
authors.forename: Charles H
authors.initials: CH
authors.lastname: Powell
authors.forename: John M
authors.initials: JM
authors.lastname: Lally
authors.forename: Lisa D
authors.initials: LD
authors.lastname: Hoong
authors.forename: Stanley W
authors.initials: SW
authors.lastname: Huth
mesh_terms: D000042:Absorption; D003198:Computer Simulation; D003261:Contact Lenses; D019544:Equipment Failure Analysis; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008956:Models, Chemical; D009883:Ophthalmic Solutions / Q000737:chemistry*
chemical_list: D009883:Ophthalmic Solutions