1 / 4

Assignment 4

Assignment 4. Briefly comment on the validity of each of the following statements:. Statement 1:

corbin
Download Presentation

Assignment 4

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Assignment 4

  2. Briefly comment on the validity of each of the following statements: Statement 1: The volume of distribution of salicylic acid is 9-12 litres in man in the usual antipyretic dose of 600mg. Therefore, the extracellular fluids contain virtually all the drug in the body. [FALSE] - Assume it is a 70kg man, the extracellular fluids volume (ECF volume) will be approx 14 L. - At first glance  May appear that virtually all the drug is in the ECF. - HOWEVER, this may not be accurate because  Vd does not represent a physical volume of any compartment. Definition: (Vd of a drug is the fluid volume in which a drug seems to be distributed to account for its plasma concentration.) - In conclusion, differential binding of drug to plasma proteins and tissue proteins could have accounted for this experimentally determined volume (9-12L).  All the drug is not confined to ECF only.

  3. Statement 2: The equilibrium distribution ratio for a drug between the liver and plasma is 50:1. Since the volume of the liver is 2.3% of body weight, Vd of the drug must be at least 75L (assume 70kg man). [TRUE] Vd = Vp + V liver . K liver = 3L + [(2.3/60).42] . 50/1 = 83.5L Vd of the drug is 83.5L (>75L) which agrees with the statement that Vd of the drug must be at least 75L.

  4. Statement 3: A drug reaches distribution equilibrium within 30 minutes (note consider short time), yet whose Vd is 200L, must distribute primarily into highly perfused organs. [TRUE] Time  30 mins (short) Vd  200L (High Vd) According to equation (Vd = Vp + V T1 . K P1 + V T2 . K P2 + …), it can be derived that Kp must be high, as Vp is only 3L. Hence 197L (200L – 3L) must be accounted for by the apparent volume of organs. Now looking at the equation: Time to convey to tissue the amount at equilibrium = Kp/(Q/VT) Since time is small and numerator (Kp) is large, it can be derived that Q/VT(perfusion rate) must be very large comparative to Kp in order to give a short time. Hence, since Q/VT is large, it validates the statement that the drug must distribute primarily into highly perfused organs.

More Related