PK + PD

Question 1

Michaelis-Menton kinetics

Answer 1

• Km = 1/2 Vmax = enzyme affinity for substrate —> lower Km = higher affinity
• competitive inhibitor increases Km
• non-competitive inhibitor(irreversible) lowers Vmax

Question 2

Lineweaver Burk plot

Answer 2

• X-intercept = -1/Km
• Y-intercept = 1/Vmax
• competitive inhib = different X-intercept
• non-comp inhib = different Y-intercept

Question 3

eqns: Vd, CL, Loading and Maintenance doses

Answer 3

• Vd = amt of drug/Cp
• CL = Vd x Ke(0.7/t_1/2)
• LD= Css x Vd
• MD= Css x CL

**assuming 100% oral bioavailability or IV infusion

Question 4

Zero vs First order kinetics

Answer 4

• zero order= constant amount of drug eliminated/time
  
  • Cp decreases linearly with time
  • PEA (Phenytoin, Ethanol, Aspirin- at toxic doses)
• first order= constant fraction of drug eliminated/time – rate of elimination is proportional to drug
  
  • Cp decreases exponentially with time
  • most drugs

Question 5

efficacy vs. potency

Answer 5

• efficacy = Vmax – non-competitive antags lower efficacy (shifts curve down)
• potency = Km – competitive antags lower potency (shifts curve to the R)

Question 6

Therapeutic index

Answer 6

• safer drugs have higher TI
• TI= TD₅₀/ED₅₀