Reversibility with sodium bicarbonate of styrene maleic anhydride, an intravasal injectable contraceptive, in male rats

PURPOSE: Patients who use topical ophthalmic medications and wear soft contact lenses must remove their lenses before drop instillation to prevent absorption of the medication into the lenses. No previous study has examined how long such a patient should wait before reinserting their lenses. This study was designed to test the hypothesis that waiting 5 minutes before reinsertion of lenses would be sufficient to reduce absorption to a level below what is needed to produce a physiological response. METHODS: Naphcon-A was used as the test solution and pupillary dilation was the physiological response measured. The amount of benzalkonium chloride (BAC) extracted from the lenses was also measured. Twenty-three subjects, none of whom had any significant ocular or systemic abnormalities nor showed pupillary dilation to directly applied Naphcon-A, completed this 3-week study. The study used a 2-period crossover design with a 1-week screening phase. Results were analyzed with a repeated-measure analysis of variance. RESULTS: The pupils averaged 0.316 mm larger when subjects instilled Naphcon-A with lenses in place as compared to when dosing with lenses removed for 5 minutes (P = 0.0008). Nine of 23 subjects showed pupillary dilation greater than 0.5 mm when dosing with lenses in place as compared to none when lenses were removed for 5 minutes. Significantly (P < 0.01) more BAC was extracted from lenses that had been worn during dosing than from lenses removed for 5 minutes (0.9 microgram/lens as compared to no detectible amount). CONCLUSION: Removing soft contact lenses for 5 minutes was sufficient to prevent absorption of clinically significant amounts of Naphcon-A into the lenses.