Highest absorption rate should be sublingual route Right?!

@@themasry5022 all parenteral bypass metabolism that doesn't mean they are fastest IV or Inhalations are much faster

+Joseph Butawo Or one hundred and fifty thousand liters ***

@@ameersaied894 doesn't matter how you spell litres/liters, same as aluminum/aluminium

Areo Saffarzadeh great video sir. The only video that made me understand volume of distribution. But i have a question, how can the plasma concentration be assumed to be the same as target tissue concentration. I mean, isn't a low plasma conc. actually means a large volume of distribution, and so more target tissue conc.???? My question is, how are they (plasma conc. and target tissue conc.) proportional if plasma conc. is inversely related to vd and vd actually determines tissue concentration? Another thing that i can't understand is that isn't the main method of drug transport in body passive diffusion, so shouldn't there be an equilibrium between plasma conc. and target tissue concentration. Please forgive these inconveniences of mine, i know my two questions contradict each other, but i really can't understand. Hope you help me, i know you posted this video 7 years ago, but let me just hope for a reply, and i appreciate your efforst so much

@Areo Saffarzadeh I'm very sorry sir, but i have another question. If a drug has high protein binding. Does this not mean it will bind to proteins and less number of it will actually be free, so theoretically and in terms of calculation, the plasma conc. should be low, and the Vd will be high. (Although it means sense that vd should be low since it never distributed).

15000 it is

Very good question raised also by others - I would like to know also.

I think it's because he is using the IV route as an example, hence the first pass elimination is not taken into account because we assume that all of the drugs are absorbed directly into the systemic circulation. If you want to consider the metabolism and elimination factor, you have to include bioavailability in the equation, like in the second example he did.. I'm not sure if it's correct though..

Hi Joe, To go into further detail there is a few Vd that you can talk about, Vd initial- i.e. prior to metabolism and redistribution into other compartments. This underestimates the Vd as there is still most of the drug in the bloodstream (i.e. blood samples taken at 1-3 min). Vd steady state relates to once the equilibrium with the major tissues is reached- this is the one most commonly used, this is samples taken at around 5-10 minutes (depending on the speed at which the drug redistributes out of the blood). The final Vd is the Vd elimination phase, which is once ALL the tissue compartments have reached equilibrium and the drug is only leaving the body by metabolism/excretion (and coming back into the blood from the tissues once the blood concentration is lower!). This greatly overestimates the Vd as the plasma concentration will be very low (and there will have been some metabolism and excretion in the time taken to reach this point). Keeping in mind, these Vd are referring to a 70kg fit and healthy male- to be able to apply them to another person they must first be divided by 70, then multiplied by the patients weight- other age / pathological features must be factored in such as: low plasma albumin in age and starvation, high body fat percentage in obesity, body water composition changes (decreasing TBW with age and dehydration), pregnancy and water/fat content changes.

+The Masry It means the total drug concentration in plasma (free drug in plasma and drug bound to plasma proteins)

kimphat18 ok thanks alot

So you take the bound fraction in consideration while measuring the drug concentration, even though the bound part won't have any effect?

+Shallu Khatri low molecular weight means the molecule will be relatively small, this increases its diffusion rate which would explain its high Vd. :)

George Burchell ohkay..got it now .. :-) Thanks :-)