For anyone struggling with his math... 70% of 300mg is 210mg entering hepatic portal system with the remaining 90mg being excreted through feces 60% of that 210mg entering the liver is deactivated by the liver resulting in 126mg of the drug being inactivated. 210mg - 126mg = 84mg or 28% of initial dose entering systemic circulation with its bioavailability intact. Hope that helps.
Hello! I didn't understand one thing why would we subtract 60% from 100% when 70% drug reaches the portal system and 30% already removed from faeces even before reaching portal??
Can you explain in your last question how it would be higher? I thought when taken orally it causes a lower effect because not everything is metabolized as opposed to parenteral route where it has a higher effect because it goes straight to circulatory. Can you explain that part?
He is asking about the dose that should be taken orally to give the same effect that IV route give so you need to make the dose higher because of the first pass effect (not asking if the effect would be higher or lower)
Not a med student but love to do health studying. This explains a lot very effectively. Thank you sir! I’m in the Data Science field so the math was refreshingly simple. It’s more of understanding processes, eh? Orally our drugs will never be 100% bioavailable.
@@physiopathopharmaco4190 it helps a lot, when explaining to my grandmother why she should seek foods that are bioavailable in b12 vs the vitamin form. And the fiber benefit and w/e. My curiosity comes from taking the right amount of vitamins + eating foods with high bioavailability of those vitamins we need. 🙂
hey, please why would you subtract 60% from 100 if 30% was already removed through faeces. shouldn't it be 60% subtracted from what got into the liver which is 70% ?
Remember that intravenous bypasses the 1st pass effect, if you are changing to oral, now you have 1st pass effect so to compensate you must increase the dose
@@aliayad5967 misunderstanding the question costs many pharma students Its almost an english test as well as a pharma test Always read the q many times over and good luck
The thing I don't understand is, I see sources that say 50% of stomach contents empty in 2.5 to 3 hours, yet oral drugs can take affect in less than an hour in some cases. If most of the drug doesn't get emptied from the stomach for hours, how does it take affect so fast? It goes directly from the stomach to the bloodstream?
My understanding would be that because the drug that doesn't get emptied is then going to systemic circulation whereas the drug that has been moved onto to be emptied has one been modified or broken down then does it have to travel through the rest of the GI system?
Please explain that why we should subtract 60% from 100% not from 70% which is the percentage of drug that gets into the liver as the 30% of drug is already being excreted into feces
Hepat Mon. 2014 Oct; 14(10): e23539. Published online 2014 Oct 11. doi: 10.5812/hepatmon.23539 PMCID: PMC4250965 PMID: 25477978. “Because of its proven safety profile (when given in recommended doses) and the lack of sedative effects and absence of nephrotoxicity, acetaminophen is the preferred analgesic in patients with liver disease including cirrhosis. However, because acetaminophen overdose is known as one of the most common cause of liver failure, it is not surprising that the majority of pain practitioners are not willing to prescribe it to patients with any form of liver disease.”
can first pass metabolism vary? like can i take a medication and one time it gets absorbed a lot and then the next not as much? can it vary based on food consumption or other factors? is it different in different people? or is it constant for a drug?
Sir please I have a question When everything exists within nature, whether it is vegetable fruits or allopathic medicine, how the body detects that allopathic medicine is a foreign material ? ? Because allopathic medicine is man made but it from a combination of the matter that exists within the nature so we consider it as natural. Then how the body detects that allopathic is foreign material ?
Though I'm far from an expert in this field, I assume anything foreign that the body encounters (after being ingested) will be absorbed and then passed through the liver. After all, vegetables and fruits are just made of organic matter that can then be broken down. This will then be absorbed into the bloodstream and can the be passed through the liver (for metabolism). This is an evolutionary mechanism I believe to make sure that the chance of any foreign molecules causing harm to humans is drastically minimised.
First pass is breakdown of the drug by the liver before it reaches systemic. Enterohepatic circulation is circulation from the gut to the portal circulation to the liver back into the bile and back into the small intestine - so its circulating from the gut to the hepatic and back to the gut and back to the hepatic in a circular pattern - so much less of it reaches systemic circulation.
@@physiopathopharmaco4190 thanks. I missed the last part of the question too. I thought is was what should you expect as it pertains to the bioavailability. Yes, the oral dose will need to be higher in order to deliver the same effect as IV. But then depending on the drug the possibility of that will need to consider other parameters.
Hi, in this case, you should multiply 20*0,7*0,4, resulting in 5,6mg. Here the explanation: 70% of the drug reaches the liver (20*0,7 = 14mg, and 6mg are lost) From the 14mg that are in the liver, 40% goes into the bloodstream (14*0,4 = 5,6mg), and 8,4mg are lost (14*0,6 = 8,4). I hope this helps you.
@@physiopathopharmaco4190 i have a doubt sir. What about Acetamonophen / paracetamol ? As iv we give 1g but while change to oral we give only 650mg. Why?
