13. Pharmacokinetics IIIII

Question 1

Describe The calculation to find Bioavailability normally and if oral dose is different to I.V. dose

Answer 1

-Referred to as F.

-Is calculated by AUC(oral)/AUC(intravenous), F=1 for an i.v. dose

-If oral dose is different the I.V. dose use equation AUC(Oral)/AUC(I.V.) X Dose(IV)/ Dose(Oral)

Question 2

Describe how to calculate rate of elimination

Answer 2

-k is the terminal rate of decrease in plasma concentrations after either an oral or I.V. dose

-K = total clearance /volume of distribution

Question 3

Describe Plasma clearance and how to calculate it

Answer 3

-The volume of plasma cleared of drug per minute

-Depends on how good the body is at eliminating that drug will be determined by the organs involved in eliminating the drug

-Every drug has a specific value

-Will be similar to the blood flow for the organ via which it is eliminated from.

-calculated as Cl= Dose X F / AUC

Question 4

Describe Half life and how to calculate it

Answer 4

-After one half life the concentration will be half of the original concentration.

-t1/2 = 0.693/k

Question 5

Describe Chronic administration

Answer 5

-continuous infusions of drug maintain a concentration within the therapeutic window.

Question 6

Describe a steady state of drug concentration and how to calculate it

Answer 6

-A steady state(Css) is met when elimination is equal to the rate of input.

-For I.V. Css =rate of infusion/ clearance

-For Oral Css = Dose X F / Dose interval X Clearance

Question 7

Describe a Loading dose and how to calculate it

Answer 7

-Drugs with long half life’s the delay to steady state concentrations may be to high so a large inital dose is given

-Loading dose for I.V = Css X v

-loading dose for oral = Css X V/F