A female client complains of periorbital aching, tearing, blurred vision, and photophobia in her right eye. Ophthalmologic examination reveals a small, irregular, nonreactive pupil — a condition resulting from acute iris inflammation (iritis). As part of the client’s therapeutic regimen, the physician prescribes atropine sulfate (Atropisol), two drops of 0.5% solution in the right eye twice daily. Atropine sulfate belongs to which drug classification?