Uptake and release of polyhexamethylene biguanide (PHMB) from hydrogel and silicone hydrogel contact lenses using a radiolabel methodology

PURPOSE: The purpose of this study was to evaluate the uptake and release of radiolabelled polyhexamethylene biguanide (PHMB) on reusable daily wear contact lenses (CLs) over 7 days. METHODS: Three silicone hydrogel (SH) contact lens materials (lotrafilcon B, balafilcon A, senofilcon A) and two conventional hydrogel (CH) materials (etafilcon A, omafilcon A) were examined. In experiment 1 (1-day study), CLs were soaked in 2 mL of phosphate buffered solution (PBS) containing radiolabelled ¹⁴C PHMB (1 µg/mL) for 8 h. The release kinetics of ¹⁴C PHMB from the CLs was measured at t = 0.25, 0.5, 1, 2, 4, 8, and 24 h in fresh 2 mL PBS. In experiment 2 (7-day study), the CLs were soaked in the ¹⁴C PHMB (1 µg/mL) solution for 8 h followed by a 16-hour release in 2 mL PBS. The lens cycle was repeated daily for 7 days. After both experiments, the residual amount of PHMB remaining within the lenses was extracted to determine the total uptake of PHMB. RESULTS: In experiment 1, the total uptake of PHMB for etafilcon A was significantly greater than senofilcon A (p = 0.01). There were no significant differences in total uptake of PHMB between other lens materials (p > 0.05). Etafilcon A released more PHMB compared to all other lens types over a 24-hr period (p < 0.001). In experiment 2, all CL materials continued to sorb more PHMB over time (p < 0.001). By day 7, the amount of PHMB sorbed by etafilcon A was significantly greater than senofilcon A (p = 0.02). After day 2, the CH materials released significantly more PHMB than the SH materials (p < 0.01). CONCLUSION: The CL materials continued to sorb PHMB with no signs of saturation after 7 days. All lens materials released a consistent amount of PHMB each day. Radioactive labelling provides a sensitive method of assessing the uptake and release of PHMB from CL materials.