10/16- Extravascular Kinetics / Pharmacokinetic Modeling

Question 1

One Compartment Model

Answer 1

CL = K x V_d

V_d = Dose / C_p

• Assumes that any changes in the Plasma level of a drug
  
  • –> reflects proportional changes in tissue drug levels

Question 2

Two Compartment Model

Answer 2

• Assumed that the drug is eliminated from the Central Compartment
  
  • Rapidly diffused with drug
  • Represents blood, water / highly perfused tissue.
• Peripheral (tissue) compartment
  
  • ​Contain tissues that equilibrate more solely with the drug.

Question 3

Extravascular

Answer 3

• implies drugs are administered OUTSIDE of systemic circulation
• Drug is moved from EXTRAVASCULAR administration site
  
  • –> Systemic circulation
  • = Absorption
  • ​​most common form of extravascular = ORAL
• Dependent only on:
  
  • Drug Absorption
  • Drug Elimination

Question 4

4 Important regions

Plasma Concentration VS Time

Curve

Answer 4

1. Initial Absorption Phase​​​
   
   1. Rise - Amount absorbed > Amount Excreted
2. Peak Drug Concentration
   
   1. ​Plateau - Amount Absorbed = Amount Excreted
   2. C_max @ T_max
3. _​Post-Absorption Phase
   
   1. ​Drop - Amount Absorbed < Amount Excreted
4. Elimination Phase
   
   1. ​No drug remains at absorption site
   2. Rate of absorption = 0

Question 5

C_max

T_max

Answer 5

• C_max = Maximum concetration of drug in plasma
  
  • _​
• T_max = time to reach C_max
  
  • _​Independent of DOSE
  • Dependent on k_a & k_el

Question 6

Lag Time

Answer 6

• Time delay between:
  
  • Admin of Single EV Dose
  • The beginning of absorption
• Factors that Contribute to lag time after oral admin:
  
  • Formulation (enteric-coated tabs)
  • Stomach Emptying