[4] Chapter 3 Pharmacokinetics Flashcards
Effects of the biologic system on drugs
Pharmacokinetics
Dose concentration relationship that deals with the processes of absorption, distribution, and elimination of drugs
Pharmacokinetics
Amount of drug reaching the plasma
Drug concentration
True or False: Drugs need to be separated so free drug is absorbed and distributed
TRUE
True or False: Tissue concentration is not proportional to plasma drug concentration
FALSE
The measure of the ability of the body to eliminate the drug, most important parameter in designing dosage regimen
Clearance
Compliance of patient is important, variation in bioavailability are usually due to variation in metabolism
Absorption
Process of delivery to interstitial and intracellular fluids
Distribution
The measure of the apparent space in the body available to contain the drug.
Volume of Distribution
It describes the predictable relationship between plasma drug concentration and concentration at the receptor site where a given drug produces its therapeutic effect.
Kinetic Homogeneity
Most appropriate time to measure drug concentration
Absorption is complete
2 hours after the dose, acidic drugs bind to
Albumin
Basic drugs bind to
Alpha 1 acid glycoprotein
True or False: The more highly protein bound drug will displace, the less protein bound drug
TRUE
Unique for a particular drug in a particular patient
Effective drug concentration
Two important parameters for effective drug concentration
Volume of Distribution, Clearance
Volume of distribution formula
Vd = (amt of drug in body)/ (plasma drug conc)
Unit for volume of distribution
Liters or Vd/kg
An increase in plasma drug concentration would result to
a decrease in volume of distribution
Drug binding to blood and plasma protein
Low distribution
Drug bound to peripheral receptors
High distribution
Clearance formula
CL=rate of elimination/plasma concentration
Unit for clearance
ml/min, L/hr, CL/body wt.
Clearance depends on:
Drug, blood flow, condition of the organs of elimination
True or False: In most drugs, clearance varies over the concentration range
FALSE
Formula for Rate of Elimination
CL * Plasma drug concentration
Rate of drug administration is equal to rate of elimination
Steady state concentration
Time it takes for concentration of a drug to fall to 50% of an earlier measurement.
Half-life (t1/2)
Unit for half life
hrs
Half life formula
t1/2 = (0.693 x Vd) / CL
True or False: Half life is dependent of volume distribution
TRUE
Bioavailability formula
F = (amount of drug in the plasma/dose of drug administered)
It is defined as the fraction of unchanged drug reaching the systemic circulation following administration by any route
Bioavailability
Fraction of the administered dose of the drug that reaches the systemic circulation
Bioavailability
Route with 100% bioavailability and has the most rapid onset, potentially immediate effects although it has increased risk of adverse effects. F=1
Intravenous
Route with 75-100% bioavailability with large volumes often feasible; may be painful, appropriate for self administration and has slow sustained from repository preparations. 0.75< F < 1
Intramuscular
Route with 75-100% bioavailability with smaller volumes than IM; may be painful. 0.75 < F < 1
Subcutaneous
Route with 5 to less than 100 % bioavailability and most convenient but first pass effect may be important, requires patient compliance. 0.05 < F < 1
Oral
Route with 30 to less than 100% bioavailability and less first-pass effect than oral
Rectal
Route with 5 to less than 100% bioavailability and often very rapid onset
Inhalation
Route with 80-100% bioavailability and usually very slow absorption; used for lack of first-pass effect; prolonged duration of action
Transdermal
Directly related to concentration
Immediate effect
Due to distributional delay
Delayed effect
Constant infusion that uses intermittent dosing only
Cumulative effect
When desired therapeutic effects are produced.
Target concentration
Plan for drug administration over a period of time. Achievement of therapeutic levels of the drug in the body without exceeding the minimum toxic concentration.
Dosage Regimens
Dosing rate formula
Dosing rate = (CL x desired plasma conc) / bioavailability
Dose needed to maintain a steady state of concentration; to maintain plasma concentration over periods of time
Maintenance dose
Loading dose formula
Loading dose = (Vd x desired concentration) / Bioavailability
Administered for drugs with long half-lives and longer time to reach a steady state; to achieve target plasma level rapidly
Loading dose
Given to promptly raise the concentration of the drug to the target concentration.
Loading Dose
True or False: If loading dose is large, dose should be given rapidly to prevent toxicity
FALSE
Most important parameter in designing dosage regimen
Clearance
Fraction or percentage of the drug removed from the perfusing blood during passage through the organ
Extraction Ratio
Drugs are eliminated unchanged or as metabolites
Excretion
Important organs for excretion
Kidneys, Liver, GIT, Breast, Lungs
Safe “opening” between the MEC and the MTC of the drug.
Therapeutic Window
It determines the desired trough levels of a drug given intermittently.
Minimum effective concentration
Determines the peak
Maximum toxic concentration
It determines the permissible peak plasma concentration
Minimum Toxic concentration / Maximum Therapeutic Concentration
