This is a bad idea. (Anesthestics in general are a bad choice for a drug OD on their own, as they were specifically developed as a safer way to induce unconciousness in surgery patients than barbiturates or opiates. Anesthestic drugs exist exactly because they're not likely to be fatal.)
The MSDS on isoflurane indicate a massive LD50 for isoflurane in both rats and mice. Lethal doses tend to be higher in bigger mammals, such as humans, so someone wanting a fatal OD would want to ingest (and keep down) a lot more than just the listed LD50 for a smaller mammal. (And keep in mind that LD50 is the amount fatal to *half* the population, which is far from a guarantee.)
hxxps://buffportal.mdc-berlin.de/data/wiki_pages/51/Sicherheitsdatenblatt_Isofluran.pdf
The oral LD50 in rats is almost 5 grams per kilo, so someone wanting to OD on this particular drugs would need to ingest over a kilogram of this for a good chance of dying. (500 grams would hit the LD50 for rats, assuming 100kgs or so of mass, but we're talking about people, not rats, and want more than a 50/50 chance, so, double it, at least.)
Ingesting (and keeping down) that much of the drug seems wildly unlikely.