Exactly, this is the reason I having been searching for a video. Because Acetaminophen has a pka of 9.5 but it is weakly acidic drug. Please can you explain the pka concept better? Thanks
Sorry dude,, we don’t want memonic for everything…we want simple understanding for things… See it clearly For weak acid: if I write equation RCOOH ~~ RCOO- + H+ At pKa of drug reaction is in equilibrium and both side 50%…if I add some H+ in solution( make pH less than 3.8) it or If I say I add more product reaction goes more to left and it should increase RCOOH concentration which is nonionized and abosrption will increase. Same for goes in reverse as said in question.. If I take out some H+ or make pH 4.8 reaction goes to right hand and will leave less drug say 10% as log works that way.
Thank you for nice explanation, i have a small doubt in the example question mentioned regarding % of unionized (Hyprophobic/lipophylic)? in case of Asprin (Weak acid) pKa is 3.8, if pH changed to 4.8 it gets ionized, So unionized form is 1% and ionized form is 10% is there any typo, that question asked? becoz its not matching the theoritical explination, please comment someone
I belive you are right, i was going to give the same example. What defines an acid or a base is its ability to donate or take protons, respectively. pKa just tells us at what pH there is a 50/50 equilibrium between ionized and non-ionized form, and how strong or weak an acid or base can be. For example, an acid with pKa of 1 is a subtance that can donate protons (so behave like an acid) even in a really acidic solution (for example with a pH=2), so it would be categroized as a strong acid. So propofol is a weak acid with a pKa of 11, in physiologic state it will mainly be in its non-ionized state (and so lipophilic state). On the other hand, etomidate is a weak base with a pKa of 4.5, so in physiologic state it will also mainly be in its non-ionized state (because when in a solution with a pH bigger than its pKa it will be difficult to aceept protons and so be in the ionized state).
Agree that the question says a ph difference of 1 unit..but you could have mentioned an example where we see the mechanism when it is an acidic or basic drug..
So how the effect of pKa on drug absorption? Did all of weak acid drug absorbed by gastric due to acid condition? When aspirin (non ionized) get absorbed by ileus, there's a gradient pH, it can make an aspirin change to ionized?
answer for case study one is wrong, as weak acid with pka 3.8, when pH increased to pH 4.8, ionized form (hydrophyllic) predominates 10% and unionized form (lipophylic) remains 1%. please check and respond if iam correct
Many thanks for your comment. However, the key to this questions is that the ratio of ionized to non-ionized forms is 1:10. Not 1% and 10%. The Henderson-Hasselbalch equation provides a ratio, not a percentage. To calculate the percentages you would need to do this: - The percentage of the hydrophobic form (non-ionized) would be 1+101 ×100=111 ×100≈9.09%. - The percentage of the hydrophilic form (ionized) would be 1+1010 ×100=1110 ×100≈90.91%. Calculating the exact percentage in the exam is seldom necessary, you just need to consider that there are 10 times more deprotonated (ionized or hydrophilic) forms than protonated (non ionized or hydrophobic) forms. This roughly corresponds to 10% of the drug being protonated (hydrophobic). We hope this explanation helped you in the way of learning always more with Lecturio. Have a great beginning of your week!
I am quite confused, the pKa suggests that this is a weak acid, and so if the pH of the surroundings it is in is 4.8, which is one pH unit higher, surely it is still put in an acidic solution, so the % of lipid solubility should be higher as most of it will exist in the nonprotonated form than protonated form, but why is the lipid solubility only 10%? Thank you!
Hi! The lipid solubility is only 10% because the Mass Law. In a high pH enviroment, weak acids tend to dissociate more, so they will be less lipophilic. Then, they will pass through the celular membranes less.
@@vittorpollux5042 I just reread through my message and turns out I seemed to have accidentally thought that high pH = high [H+] when it is the opposite way around but it makes a lot more sense, thank you for the reply!
Jehovah will draw those so we don't worry when sharing simple message...Love smile great as friends ...literature we have plenty just Be out There 😁🥰 ACE
What you are saying here is againts First Aid 2022. In First Aid 2022 on page 233 it is mentioned that weak bases are trapped in acidic environment. Here in pyrimethamine explanation you say that is more soluble in Acidic pH while itself is a weak base. Weak bases are trapped in acidic pH, they are more soluble at higher pHs as opposed to what you explained here. Please reply. Also your slide on drug solubility at 3: 46 mins is completely wrong. Weak bases are NOT more soluble when protonated. They are trapped (insoluble) in acidic pHs because they are BASES. Also acids are more soluble when protonated. It is totally wrong. Please see First Aid 2022 page 233. There is a graph over there. If I am wrong, guide me. But if you are wrong, correct the video please. Weak acids trapped in basic environment, soluble in acidic environment. Weak bases trapped in acidic environment, soluble at higher pHs.
You took a simple topic , made it way more confusing than it should be and then had to refer to a mnemonic to remember everything. This is the definition of pathetic teaching.
Thank you. This was a good review for my pharmacology final. Wish me luck.
Thanks so much. I love the way you explain this- its the best explanation I have found on youtube so far. The visual tools are so helpful.
Pka does not determine whether the drug is acidic or basic.
Exactly, this is the reason I having been searching for a video. Because Acetaminophen has a pka of 9.5 but it is weakly acidic drug. Please can you explain the pka concept better? Thanks
Best practical video I have watched so far on this topic. Thank you very much, Sir.
Unfortunately, you cannot tell from the pKa of a drug whether it is basic or acidic...
NB: PKa doesn’t distinguish whether drug is acid or base.
Sorry dude,, we don’t want memonic for everything…we want simple understanding for things…
See it clearly
For weak acid: if I write equation
RCOOH ~~ RCOO- + H+
At pKa of drug reaction is in equilibrium and both side 50%…if I add some H+ in solution( make pH less than 3.8) it or If I say I add more product reaction goes more to left and it should increase RCOOH concentration which is nonionized and abosrption will increase.
Same for goes in reverse as said in question..
If I take out some H+ or make pH 4.8 reaction goes to right hand and will leave less drug say 10% as log works that way.
That's awesome ❤️
Thank you so much. You’re such a blessing
How can I tell if I don't know if the drug is acidic or basic?
Thanks my dude
Oh can't thank you enough!! You makes this annoying thing so easy...
Complete detailed notes on my UA-cam channel
@@AbhiPharmacy Thank you. Will see it soon then!🙂
Very good presentation.
Thank you for nice explanation, i have a small doubt in the example question mentioned regarding % of unionized (Hyprophobic/lipophylic)? in case of Asprin (Weak acid) pKa is 3.8,
if pH changed to 4.8 it gets ionized, So unionized form is 1% and ionized form is 10%
is there any typo, that question asked? becoz its not matching the theoritical explination,
please comment someone
a drug having a PKA of less than 7 does not make it a weak acid. Propofol has a PKA of 11 and it is a weak acid. Am I missing something. Thank you.
I belive you are right, i was going to give the same example. What defines an acid or a base is its ability to donate or take protons, respectively. pKa just tells us at what pH there is a 50/50 equilibrium between ionized and non-ionized form, and how strong or weak an acid or base can be. For example, an acid with pKa of 1 is a subtance that can donate protons (so behave like an acid) even in a really acidic solution (for example with a pH=2), so it would be categroized as a strong acid.
So propofol is a weak acid with a pKa of 11, in physiologic state it will mainly be in its non-ionized state (and so lipophilic state). On the other hand, etomidate is a weak base with a pKa of 4.5, so in physiologic state it will also mainly be in its non-ionized state (because when in a solution with a pH bigger than its pKa it will be difficult to aceept protons and so be in the ionized state).
Agree that the question says a ph difference of 1 unit..but you could have mentioned an example where we see the mechanism when it is an acidic or basic drug..
At 2.24 for weak acid, does that mean when the pKa increases, more of the Aspirin will be dissociated and ionized?
Great video..Thank you
Complete detailed notes on my UA-cam channel
I knew the answer but i was confused about one concept but it's clear. Thankyou sir
thank you
In time 3:10, what you say is not what you show in your slide. This makes a huge confusion.
So how the effect of pKa on drug absorption? Did all of weak acid drug absorbed by gastric due to acid condition? When aspirin (non ionized) get absorbed by ileus, there's a gradient pH, it can make an aspirin change to ionized?
pH 7 for neutral above=base, below=acids. Is there same thing in case of pka means can we say that above pka 7 is base
thanks
answer for case study one is wrong, as weak acid with pka 3.8, when pH increased to pH 4.8, ionized form (hydrophyllic) predominates 10% and unionized form (lipophylic) remains 1%. please check and respond if iam correct
Many thanks for your comment. However, the key to this questions is that the ratio of ionized to non-ionized forms is 1:10. Not 1% and 10%. The Henderson-Hasselbalch equation provides a ratio, not a percentage. To calculate the percentages you would need to do this:
- The percentage of the hydrophobic form (non-ionized) would be 1+101 ×100=111 ×100≈9.09%.
- The percentage of the hydrophilic form (ionized) would be 1+1010 ×100=1110 ×100≈90.91%.
Calculating the exact percentage in the exam is seldom necessary, you just need to consider that there are 10 times more deprotonated (ionized or hydrophilic) forms than protonated (non ionized or hydrophobic) forms. This roughly corresponds to 10% of the drug being protonated (hydrophobic).
We hope this explanation helped you in the way of learning always more with Lecturio. Have a great beginning of your week!
Very interesting, thank you.
This was soooo helpful!
pKa of less than 7 means it's an acid?
What about weak bases such as ketoconazole?
That wrong, pka does not determine whether a drug is acidic or bases.
@@zarakristen2967
Exactly! He should have mentioned if the drug was acidic or basic right??
How did he give the answer without it
now it's clear. Thank you
I am quite confused, the pKa suggests that this is a weak acid, and so if the pH of the surroundings it is in is 4.8, which is one pH unit higher, surely it is still put in an acidic solution, so the % of lipid solubility should be higher as most of it will exist in the nonprotonated form than protonated form, but why is the lipid solubility only 10%? Thank you!
Hi! The lipid solubility is only 10% because the Mass Law. In a high pH enviroment, weak acids tend to dissociate more, so they will be less lipophilic. Then, they will pass through the celular membranes less.
@@vittorpollux5042 I just reread through my message and turns out I seemed to have accidentally thought that high pH = high [H+] when it is the opposite way around but it makes a lot more sense, thank you for the reply!
@@aashav2573 Oh yeah! No problem, it is a little common mistake hehe
Jehovah will draw those so we don't worry when sharing simple message...Love smile great as friends ...literature we have plenty just Be out There 😁🥰 ACE
What you are saying here is againts First Aid 2022. In First Aid 2022 on page 233 it is mentioned that weak bases are trapped in acidic environment. Here in pyrimethamine explanation you say that is more soluble in Acidic pH while itself is a weak base. Weak bases are trapped in acidic pH, they are more soluble at higher pHs as opposed to what you explained here. Please reply.
Also your slide on drug solubility at 3: 46 mins is completely wrong. Weak bases are NOT more soluble when protonated. They are trapped (insoluble) in acidic pHs because they are BASES. Also acids are more soluble when protonated. It is totally wrong. Please see First Aid 2022 page 233. There is a graph over there. If I am wrong, guide me. But if you are wrong, correct the video please.
Weak acids trapped in basic environment, soluble in acidic environment.
Weak bases trapped in acidic environment, soluble at higher pHs.
Hi, I'll forward your comment to our content team! When I know more I'll update you :)
Any updates?@@lecturiomedical
@@Rafiq2024A It was forwarded to our content team and will be checked :)
I'll answer you here when I know anything more :)
@@Rafiq2024A Small update: The content team checked the video and is aware of issues with it and is in the process of producing a correct version.
Anyone else here from the PKA Podcast?
You took a simple topic , made it way more confusing than it should be and then had to refer to a mnemonic to remember everything. This is the definition of pathetic teaching.
This lecture is cringeworthy from a chemist's point of view.