A 52-year-old woman with a history of overactive bladder (OAB) has been on oxybutynin 5 mg twice daily for 6 months with good symptom control. She now presents with complaints of severe constipation, dry mouth, and difficulty reading (blurred near vision). She is also experiencing cognitive slowing and occasional confusion. Her daughter is concerned about her memory. On examination, her pupils are mildly dilated and her mouth is dry. Which of the following strategies would be most appropriate to manage her anticholinergic adverse effects while maintaining OAB control?