Pharmacokinectics Flashcards
Define pharmacokinetics.
The mathematical description of plasma concentration-time course
What are the factors for dose regimen?
1: Dosage
2: Route of administration
3: Frequency
4: Duration of administration
What are the factors for optimum dosage regimen?
1: Effective
2: Nontoxic
3: Without prolonged drug residues in tissues of food animals
Define rate of absorption.
The time to peak plasma concentration (tmax)
How is the extent of absorption measured?
By systemic bioavailability (F%)
Define systemic availability.
The fraction of the dose which reaches the systemic circulation intact
What is the formula for systemic availability?
F% = (Area under the curve X 100)/Area under the curve IV
Define compartment.
The tissues and organs for which the rates of uptake and subsequent clearance of a drug are similar
Define one-compartment model.
All tissues and organs which the drug penetrates as if they were in ready equilibrium with the blood.q
Define rate of distribution
Estimated by the distribution phase half-time (t1/2alpha) in the two-compartment model
How is the extent of distribution measured?
By the apparent volume of distribution
Define apparent volume of distribution.
The volumes of fluid which would be required to contain the amount of the drug in the body if it were uniformly distributes and the concentration in that fluid was equal to the concentration in the plasma.
Define dose IV
The amount of drug in the body
What is Vd (l/kg)?
amount of drug in the body (D)/plasma drug concentration (Cp)
What is the formula for IV the Vd (L/kg)?
Dose (mg/kg)/Cp (mg/L)
What is the formula for extravascular the Vd (L/kg)?
(D (mg/kg) X F%)/Cp (mg/L)
When Vd < 1L/kg, the drug _____.
Has a limited distribution (tends to stay in the plasma)
When Vd = 1L/kg, the drug _____.
Has a wide distribution
When the Vd > 1L/kg, the drug _____.
Has a very wide distribution
How is elimination measured?
By half-life (t1/2) or total body clearance (CLb)
Define half-life (t1/2).
The time required for the body to eliminate 1/2 of the drug it contains.
Elimination of most drugs follow _____.
1st order kinetics
Define 1st order kinetics.
The rate of removal of drug from the plasma is proportional to the concentration present at a given time (a constant % of drug is eliminated per unit time)
Define zero order kinetics
The rate of elimination remains constant regardless of the amount of drug in he body (a constant amount of drug is eliminated per unit time)
What order does aspirin in cats and phenylbutazone in dogs follow?
Zero order kinetics
What does the half-life determine?
The rate at which plasma concentration of a drug rises during constant IV infusion to attain a steady-state concentration
Define steady state concentration.
The plasma concentration of drug when the maintenance rate of drug administration is equal to the rate of elimination.
Define total body clearance (CLb)
The rate of drug elimination from the body by all routes relative to the concentration of drug in plasma
What is the formula for CLb?
CLb = CLr + CLnr
Define plasma clearance (CLp)
The volume of plasma cleared of the drug per unit time (mL/min.)
What is the formula for CLp?
CLp = rate of elimination (mg/min)/plasma drug concentration (mg/mL)
What is the formula for rate of elimination?
Rate of elimination (mg/min.) = urine flow (mL/min.) X concentration of drug in urine (mg/mL)
What is the calculation of half-life?
CLb = (Vd X (k))/t1/2
Define extraction ration
The fraction of the drug removed from the perfusing blood by an organ
What is the formula for extraction ration?
E = (Ca - Cv)/Ca
What is Ca?
The concentration of drug in the arterial blood entering the organ
What is Cv?
The concentration of drug in venous blood leaving the organ
What is the formula for elimination?
Cl(organ) = Q times E
What is Q?
Blood flow to the organ
What is E?
Extraction ration
What are some of the drugs that have high hepatic extraction?
1: Lidocaine
2: Propanolol
3: Diazepam
4: Nitroglycerin
What is the formula for dosing rate?
Dosing rate = clearance X desired steady-state concentrtion
What is the formula for daily dose?
Daily dose = dose/min X 60 (min/hr) X 24hrs
Dose X F = _____.
CLb X Cp(ss)
What is the formula for loading dose?
Vd X desired serum drug concentration
What is the formula for adjusted dose?
Adjusted dose = (normal dose X patient’s renal clearance)/normal renal clearance
What is the formula for adjusted dose interval?
Adjusted dose interval = (normal dose interval X normal clearance interval)/patient’s renal clearance
What is renal clearance usually estimated by?
Creatinine clearance
