Kidney Stone Teaser

A patient is a recurrent stone former. The stones are conformed to be calcium oxalate. You put him on UroCitK and he is stone free for 3 years. But he gets lazy and stops taking the drug.

He then gets started on a drug for migraines which works great. Migraines stop.

Six months later he develops an acute stone. The stone is removed by urology and identified as calcium phosphate. What was the migraine
drug?