The antibiotic Flagyl, also known as metronidazole lowers your body's ability to metabolize many things, among which is propelyne glycol. It affects your metabolism so much that even a small amount of propelyne glycol can make you sick, vomit, or even have seizures due to it building up in your system. Those who vape even low PG juices will still be affected. I use 20/80 PG/VG juices and just a few puffs will make me feel so sick I can't stand up. There are accounts of others being hospitilized, although they are secondhand so I'm not sure of the validity. But this is something that definitely needs to be discussed with those receiving these medicines, as I am currently.