Iwan asked
I was prescribed Metronidazole and ciprofloxacin today to treat diverticulitis, and I've read that you shouldn't have alcohol or Propylene Glycol while on Metronidazole. use an electronic cigarette juice that contains Propylene Glycol. I have just stopped vaping for the night (10:30PM), but I am concerned about taking the Metronidazole tomorrow morning. I plan to take it at about 9:30AM. Is this safe, or do I need to wait longer for the propylene glycol to leave my system before starting the medication?
Answer
While taking Metronidazole (Flagyl), consumption of both alcohol and propylene glycol are contraindicated until at least three days after taking the last dose.
This is because the interaction between alcohol, propylene glycol and metronidazole can cause serious side effects such as:
- Abdominal cramps
- Nausea
- Vomiting
- Headaches
- Flushing
Propylene glycol is a commonly used ingredient in e-cigarettes liquids and other vape "juices". Propylene glycol is often added to solubilize the components of these liquids.
How Metronidazole Interacts With Alcohol And Propylene Glycol
Alcohol and propylene glycol are primarily metabolized via alcohol dehydrogenase, aldehyde dehydrogenase, cytochrome P450 (CYP2E1), and catalase.
The byproducts of alcohol include acetaldehyde and acetate and contribute to many of the negative effects. In addition, byproducts of propylene glycol include propionaldehyde, a potentially toxic compound.
Some drugs, like metronidazole, may cause a “disulfiram-like reaction” when taken with alcohol or propylene glycol. These drugs inhibit aldehyde dehydrogenase which is crucial in metabolism of alcohol and propylene glycol. This can cause flushing, nausea, vomiting, and general “hangover effects”.
While the interaction with metronidazole and alcohol is well known, the interaction with propylene glycol has fewer documented reports.
Nevertheless, Propylene glycol is metabolized by the alcohol and aldehyde dehydrogenase enzyme pathway.
When taken with metronidazole, our bodies may not be able to adequately metabolize and eliminate propylene glycol, thereby leading to its accumulation and potential adverse events. In addition, we may not be able to eliminate the propylene glycol byproduct propionaldehyde as efficiently either.
The package insert strongly recommends against using alcohol and propylene glycol with metronidazole:
"Use of oral metronidazole is associated with a disulfiram-like reaction to alcohol, including abdominal cramps, nausea, vomiting, headaches, and flushing. Discontinue consumption of alcohol or products containing propylene glycol during and for at least three days after therapy with metronidazole."
Evidence Behind Metronidazole - Alcohol - Propylene Glycol Interaction
The published evidence regarding the interaction isn't exactly clear and concise.
There have been case studies pointing to the interaction causing severe side effects and even death. However, other small studies did not show that metronidazole increased acetaldehyde levels in the blood or cause any noticeable adverse events.
Unfortunately, there are no large studies analyzing this interaction and it is possible that some groups of people are more susceptible to having significant adverse reactions.
Nevertheless, because the potential adverse effects of taking metronidazole with alcohol or propylene glycol are significant, it would be smart to wait to drink alcohol or use e-cigarettes/vape juices that contain propylene glycol until the risk of disulfiram-like reaction is decreased (3 days after your last metronidazole dose).
