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What Causes Drug Interactions? E.g. Tylenol (acetaminophen) & Alcohol | 25th Week in Medical School

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I’m not a doctor. I’m just a first year medical student. This isn’t medical advice. What do I know?

What’s up you guys rex here quick video today on how drug drug interactions work and specifically why it’s probably not a good idea to take a lot of tylenol if you also drink a lot of alcohol so this was a really fun week in medical school because i got to learn something i’ve wondered about for a long time so i’m a first year medical student and something i do

Every week is share a little tidbit that i learned in my past week of medical school so i finally had the question answered of sort of how drug drug interactions work now i did understand how sort of like i covered last week a drug can interact with another drug if they both act on the same receptor so last week i talked about how both ibuprofen and aspirin

Can act on the cox-1 enzyme and they both inhibit that enzyme by binding to it so it makes sense that they can interact with each other but i always didn’t understand how two drugs even if they don’t have any sort of similar function can have an interaction that can be potentially dangerous and so the reason for most drug interactions comes down to how our liver

Metabolizes drugs and gets them out of our body so there’s generally two ways our liver does this we can talk about phase one metabolism and phase two metabolism without getting into too much detail basically the goal of phase one metabolism is to modify the drug itself in some way to make it more polar so that it can be water soluble the point of this is that

If it’s water soluble it can get trapped in the blood and then in the urine and be trapped in the urine and excreted from the body there’s also metabolism that happens in the small intestine and within the kidneys themselves but for now we’ll just talk about the liver and then phase two metabolism is where we actually take some molecule inside the body and hook

It onto the drug and that can deactivate it and also make it more water soluble and so it can get trapped in the iron and excreted so we have phase one which is to change the drug itself and phase two is to hook some other molecule onto the drug and what actually carries out phase one metabolism in the liver is a huge family of enzymes for the most part called

The cytochrome p450 enzymes and so these enzymes have all kinds of different functions for different drugs but the way drug interaction happens is it’s interesting that different drugs can either induce specific enzymes to function more or inhibit them so they can induce them by causing more production of these enzymes or cause them to last longer once they are

Produced so they have more effect or it can inhibit these enzymes and this can have different effects depending on the two drugs at play so if one drug induces this enzyme to work more then if you give another drug that’s normally broken down by it it’s going to get broken down much faster and depending on if it’s a drug that acts in its active form when it’s

First in the body and then it’s metabolized into an inactive form that would decrease the activity of that drug so you need a greater drug dose to have the same level of activity or there’s things called a pro drug where you give it in an inactive form and when it’s first metabolized it becomes active so if you have a different drug that is inducing the enzyme

In the liver the cytochrome p450 enzyme that breaks down this pro drug into its active form if you are just giving the standard dose you might actually have a toxic level of the pro drug produced very quickly that you wouldn’t expect which can lead to a very dangerous drug drug interaction and so now quickly the really interesting mechanism for how tylenol or

Acetaminophen and alcohol interact so acetaminophen metabolism is actually very interesting that ninety percent of it actually happens under the phase two pathway so usually the phase two pathway and then like ten percent goes down the phase one pathway and within the phase one pathway there’s actually sort of a choose your own adventure where it can go one way or

The other way and so the one way is down the 2e1 cytochrome p450 enzyme pathway and if it goes down that way that actually creates a dangerous and toxic substance to our liver that can cause severe liver damage now when you normally take tylenol it’s ninety percent going down the phase two pathway so only ten percent is starting with this phase one pathway and

Then only a very small amount of that 10 percent actually goes down this 2e1 pathway that causes liver damage now what’s interesting is alcohol even though the majority of alcohol is broken down by alcohol dehydrogenase or aldehyde dehydrogenase a small amount of the metabolism is done by 2e1 and alcohol actually induces 2e1 so that there is more activity of

2e1 especially if you drink alcohol a lot and very frequently 2e1 gets more and more prevalent in your liver so that it can help with breaking down alcohol so now if you take tylenol and especially if you take a lot of it that you maybe saturate the phase 2 pathway that normally does 90 now instead of 90 maybe it only can do 80 and so now 20 is going down the

Phase one pathway but now this 2e1 is really induced by alcohol a ton more goes down that toxic pathway that can cause liver damage and so that’s super interesting to me that even though alcohol and tylenol have no like similar effects as far as what they are doing on the body they converge in a very specific pathway in how they are broken down that can lead

To an interaction where a lot of alcohol use for an extended chronic period of time can lead to taking acetaminophen yielding toxic effects to our liver that can be dangerous and so that was a really interesting example of drug drug interaction and finally answered a question to me so if you learned anything new or if you have any questions comments or concerns

Leave them down below i’ll read and respond to every single comment if you want to catch more of my videos where i share cool things i learned in medical school or share things about the medical school application cycle make sure you subscribe hit the notification bell as always like the video if you liked the video dislike the video if you disliked the video and

Until next time don’t be ordinary go be great

Transcribed from video
What Causes Drug Interactions? E.g. Tylenol (acetaminophen) & Alcohol | 25th Week in Medical School By Doctor (someday) Rex MS2