L42 - IV Bolus Administration 2 Flashcards
What is apparent volume of distribution?
volume into which a drugs distributes in the body at equilibrium
What is V having a given Cplasma of the drug?
V = Abody/Cplasma
What is V used for?
- relatin A and Cp
- estimating dose required to achieve a given conc (Crequired)
- bolus dose = V x Crequired
What are loading dose and V like in one compartmental model?
Volume of the compratment equals the volume of distribution
What is the eqn to estimate the volume of distribution with IV bolus data?
Volume = amount of drug in the body / drug conc in plasma
What does the calculation of V require?
- eq of distribution achieved
- amount of drug in the body (Abody) and the drug concentration (Cplasma) at the same time
What is the eqn for V in the one compartment model?
- V = dose/C0
- bc A = A0 = dose and Cp = C0
- where C0 is the plasma conc that result from instantaenous distribution of the dose into volume of distribution
What is clearance like in regards to IV bolus?
Cl is the proportionality factor relating dA/dt to Cp
How do you calculate k, taking Cl into account?
K = Cl/V
What can the half life of a drug be used to predict?
- how quickly the drug conc will decline in plasma
- how quickly amount of drug in the body will decline
- time to reach Css in an IV infusion
- time to reach Css in multiple doses regimen
What is half life in terms of drug in the body?
Time rquired for the drug conc in the body to fall by one half
what is the eqn for elimination half life?
T1/2 = 0.693/k
what is the eqn for elimination half life? (Including Cl)
T1/2 = 0.693V/Cl
How do you use half life for predictions?
- express k as a function of t1/2
- time post injection as function of half lives elapsed since injection
What are the eqn when using half life for predictions?
- C = C0 x e^-kt
- C = C0 x e^-(0.693/t1/2)t
- C = C0(1/2)^n
What can the are under th curve be used for?
- express the body exposure to a drug, link to therapeutic and toxic response
- determine Cl of a drug
- estimate bioavailability of an extravascular formulation
- asses the bioequivalance of two formulatino
What is the AUC in the one-compartmental model?
AUC(infinite)0 = C0/k
How do you demonstrate AUC and Cl link?
AUC(infinite)0 = D/kV
= D/Cl
How is AUC used to estimate Cl of a drug? (Eqn)
Cl = dose/AUC(infinite)0
What is the simplest way to obtain AUC?
Trapezoidal rule
Area of each trapezoid - (B + b) h/2
When can AUC(infinite)0 = C0/k be used?
- when the only process is elimination - IV bolus, post infusion phase, terminal phase
- PK of a drug are linear and well described by 1compartment model
What is AUC also used for?
- estimate bioavailability
- reflects max body exposure to dose given
- reflect the extent of absorption (extravascular administration)
What is the absolute bioavailability?
Ratio of the AUC obtained with an extravascular formulation and AUC(IV)
