A 38-year-old woman is brought to the hospital with a 2-week history of progressive weakness, paresthesias in her hands and feet, and gastrointestinal disturbances. Her husband mentions she has been consuming homemade cosmetic creams purchased from an unlicensed vendor for the past 6 months to lighten her skin. On examination, she has hyperpigmentation on the face with a characteristic 'Mees' lines' on her fingernails, and peripheral neuropathy. Her blood arsenic level is 45 µg/dL (normal <10 µg/dL). What is the most likely diagnosis and the appropriate chelating agent?