Trigeminal neuralgia

A 55-year-old woman comes to the office due to 2 months of episodic jaw pain. She describes sharp shooting, “shock like” pain over the left side of her jaw that typically lasts for a few seconds. She has noticed a few times that the pain has occurred while she was eating dinner, and once while she was brushing her teeth. Physical examination shows no abnormalities. The patient is started on the first line medication for her condition. During her one month follow-up appointment, she states that her symptoms have improved significantly, but she describes feeling some dizziness and instability. Which of the following is the mechanism of action of the medication being used by this patient?