The short version
Just 3 companies supply this market — thin enough that a single exit would be felt immediately. The price has jumped 31% in a year, to $0.0038 per mL — sharp rises like this often mean supply is already tightening. Historically, drugs in this position went on to a new shortage within 90 days about 0.8% of the time — roughly 5× the typical drug (0.1%).