Pharmacokinetics Flashcards
A dosage regimen includes:
dosage
route of admin
frequency
duration of admin
The optimum dosage regimen is described as?
effective
nontoxic
w/o prolonged drug residues in tissues of food animals
pharmacokinetic definition
the mathematical description of the plasma concentration-time course
the mathematical description of the plasma concentration-time course
pharmacokinetics
is the time to peak plasma concentration (Tmax)
rate of absorption
rate of absorption is..
the time to peak plasma concentration (Tmax)
the extent of absorption is measured by
systemic bioavailability (F%)
When you measure systemic bioavailability you are determining the…
extent of absorption
what is the fraction of the dose which reaches the systemic circulation intact
systemic bioavailability
systemic bioavailability (F%) =
AUC extravasc x 100 / AUC IV
AUC stands for
area under the plasma concentration-time curve
compartments refers to
those tissues and organs for which the rates of uptake and subsequent clearance of a drug are similar
one-compartment model
all tissues and organs which the drug penetrates behave as if they were in ready equilibrium with the blood
rate of distribution
estimated by the distribution phase half-time (t1/2a) in the two compartment model
extent of distribution
measured by the apparent volume of distribution Vd
can be defined as the volume of fluid which would be required to contain the amount of the drug in the body if it were uniformly distributed, and the concentration in that fluid was equal to the concentration in the plasma
apparent volume of distribution (Vd)
Vd(L/kg)=
amount of drug in body (D) / plasma drug concentration (Cp)
the amount of drug in the body =
the dose IV
for IV the Vd(L/kg) =
Dose (D) (mg/kg) / Cp (mg/L)
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 plasma)
When Vd = 1L/kg -
the drug has a wide distribution
When Vd > 1L/kg -
the drug has a very wide distribution
elimination is measured by
half life or total body clearance
half life is the time required for
the body to eliminate 1/2 of the drug it contains
elimination of most drugs follows ____
first order kinetics
first order kinetics means
the rate of removal of drug from the plasma is proportional to the concentration present at a given time (a constant percent of drug is eliminated per unit time)
which drug in cats follows zero order kinetics
aspirin
which drug in dogs and horses follows zero order kinetics
phenylbutazone
If your drug concentration in plasma is 10mg/ml then what is the first half life concentration
5mg/ml
the half life determines…
the rate at which plasma concentration of a drug rises during constant IV infusion to attain a steady-state concentration
is the plasma concentration of drug when the maintenance rate of drug administration is equal to the rate of elimination
steady-state plasma concentration or plateau (Cp(ss))
how many half lives till plasma conc. reaches 93.75%
4 half lives
about what percent of the steady state concentration is achieved in 3.3 half lives
90%
a faster rate of infusion does not change the time needed to achieve steady state; what does change
the steady state concentration Css, changes
the rate of drug elimination from the body, by all routes, relative to the concentration of drug in plasma
total body clearance
CLB=
CLr+ CLnr
the volume of plasma cleared of the drug per unit time (mL/min)
plasma clearance (CLp)
plasma clearance (CLp)=
rate of elimination (mg/min) / plasma drug concentration (mg/mL)
the rate of elimination (mg/min)=
urine flow (mL/min) X concentration of drug in urine (mg/mL)
clearance is related to the
Vd
T1/2
elimination rate constant (k)
CLB=
Vd X 0.693 / t1/2
the fraction of the drug removed from the perfusing blood by an organ
extraction ratio
extraction ratio (E) =
(CA_)- CV/ CA
CA is
the concentration of drugs in arterial blood entering the organ
CV is
the concentration of drug in venous blood leaving the organ
Cl organ =
Q x E
Q is
blood flow to the organ
E is
extraction ratio
list 4 examples of drugs that have high hepatic extraction ratio
lidocaine
propranolol
diazepam
nitroglycerin
dosing rate =
clearance X desired steady state
the daily dose =
dose/min X 60 min per hour X 24 hours
loading dose=
Vd X desired serum drug concentration
adjusted dose for renal disease =
normal dose X (patients renal clearance / normal renal clearance)
adjusted dose interval for renal disease=
normal dose interval X (normal renal clearance/ patients renal clearance)
renal clearance is usually estimated by
creatinine clearance
which of the following is NOT an age-related factor to consider when dosing a neonate? A. increased plasma protein binding B. increased total body water C. decreased drug metabolism D. decreased blood brain barrier
Increased plasma protein binding
ruminants have a tolerance to barbiturates is an example of \_\_\_\_ A. cross tolerance B. tachyphylaxis C. natural tolerance D. acquired tolerance E. down regulation of receptors
natural tolerance
what two diseases can decrease renal excretion
Kidney disease and congestive heart failure
which is an example of an undesirable drug interaction?
A. amino glycoside antibiotic + amino glycoside antibiotic
B. chloramphenicol + phenobarbital
C. aminoglycoside AB + muscle relaxant
D. A & C
E. all of the above
all above
potentiation is a drug to drug interaction where there is ____ of drug effects
intensification
alteration of distribution is the pharmacokinetic interaction in which…
strongly bound drugs to plasma proteins displace weakly bound drugs increasing their effects
which is not a dosing factor to the environment? A. humidity B. atmospheric pressure C. ambient temp D. oxygen
atmospheric pressure
drug reactions that are genetically determined, abnormal, unpredictable and caused by reactive drug metabolites are called…
idiosyncratic drug reactions
a vet must consider which of the following factors before dosing a geriatric animal?
reduction in plasma albumin
morphine effects vary by species: T/F?
true
boxers are sensitive to which drug?
phenothiazine
chronic phenobarbital therapy can cause hyperactivity in children: T/F?
false
route of admin can modify what?
onset of action
duration of action
