compartmental PK

Question 1

what is the effective dose and what factors affect this

Answer 1

amount of parent drug that reaches systemic circulation
1. salt factor (drugs are in salt form to help them reach active site)
2. bioavailability factor. (if not given by IV a portion of drug might be lost)

Question 2

what are the components of compartmental analyses

Answer 2

imaginary units to represent tissues/group of tissues with similar rates of distribution (some tissues take up drug more than others at diff. rates) highly perfused tissues have more drug distribution
central compartment (1) : plasma/blood
generally 1-3 compartments used.
2 is highly perfused tissues.

Question 3

what is the rate of drug absorption dependent on

Answer 3

first order rate constant of absorption (KA) (reaction rate dependent on concentration of one ligand) and amount of drug in GI.

Question 4

what are the assumptions made in compartmental analyses.

Answer 4

simplest pK model
elimination assumed to occur through central compartment only.
distribution is instantaneous

Question 5

what are some assumptions of one compartmental models

Answer 5

1. distribution to tissues is instantaneous and homogenous.
2. elimination is through central compartment and plasma conc. is only influenced by elimination
3. no recirculation
   first order elimination (constant proportion eliminated through time) straight line of cp to time

c1=cp
A1= ab
v1=a1/cp is =vd

Question 6

what are the stages of two compartmental cp over time

Answer 6

first stage: distribution to peripheral compartment (gradual exchange between central and peripheral until equilibrium)
second stage: elimination phase (less steep straight line)
central compartment consists of CP and tissues that take up drug rapidly whereas the peripheral component consist of slower uptake tissues.

redistribution and distribution are both first order processes.

Question 7

what are characteristics of three compartmental model

Answer 7

distribution from central to third (deep) and second (peripheral) compartment and elimination
assume that distribution is instantaneous
1. distrib. to peripheral linear first order.
2. elim. and redistribution phase. two straight lines

Question 8

what is the difference between iv bolus and iv infusion

Answer 8

bolus: whole dose delivered at one time (high initial plasma conc)
infusion: delivery extended over longer period at constant rate