40 Questions
In the two-compartment open model, which compartment is supposed to contain slowly equilibrating tissues?
Central compartment
What is the determining factor for the categorization of the two-compartment model?
Rate of equilibration
Which type of two-compartment model assumes drug elimination from the central compartment?
Two compartment model with elimination from central compartment
What characterizes the decline in plasma concentration in the two-compartment model after an intravenous injection?
Biexponential distribution
In the two-compartment model, where does the drug require some length of time for equilibration?
Central compartment
Which tissues are considered highly perfused in the two-compartment model?
Lungs, kidney, etc.
What state is achieved between the central compartment and the more poorly perfused tissue compartment after some time?
Pseudo-distribution equilibrium
Which compartment in the two-compartment model assumes the rest of the organ in the tissue compartment?
Peripheral or Tissue Compartment
What does the rapid decline in the two-compartment model result from?
Initial rapid decline in the central compartment
What is the state of equilibrium achieved between the central compartment and the more slowly perfused tissues in the two-compartment model?
Pseudo-distribution equilibrium
Which model assumes no drug in the tissue compartment at time $t=0$?
Two-compartment model
What is the sum of the apparent volume of distribution ($V$), Vi, and Vt in the two-compartment model?
Vi + Vt
What can inaccurate prediction of target organ location in Vi or Vt lead to?
Toxic effects
What is an example of a drug that follows the principle of two-compartment modeling?
Potassium
What may be missed if blood is sampled too late after drug administration in the two-compartment model?
Distribution phase
What type of rate constants are involved in the two-compartment model for drug transfer between central and peripheral compartments?
First order
What should loading doses of drugs account for in the two-compartment model?
Drug distribution into tissue compartment
What can slow drug distribution into the tissue compartment pose problems in?
Interpretation of drug concentrations
What are guidelines for rates of drug administration often based on in the context of two-compartment modeling?
Clinical response receptors
What cannot be used to predict drug effects if obtained before complete distribution in the two-compartment model?
Plasma samples
In the two-compartment model, which phase represents the distribution of drug from Vi into Vt?
Alpha phase
What characterizes drugs that behave in a way referred to as 'non-significant two compartment drugs'?
They exhibit relatively little drug elimination during the distribution phase.
What can increased drug plasma concentrations during the alpha phase lead to for drugs with 'non-significant' two compartment modeling?
Clinically significant serious toxicity
For drugs that exhibit significant drug elimination in the alpha phase, what can be expected in terms of actual trough concentrations compared to those predicted by a one-compartment model?
Lower actual trough concentrations
What is the consequence of obtaining samples in the distribution phase for drugs with 'significant' two compartment modeling?
Very similar pharmacokinetic interpretations are usually arrived at using simpler one-compartment model
In the context of two-compartment modeling, what does Vi represent?
Initial volume of distribution
What is the term used for drugs that border on having significant two compartment modeling?
Drugs with 'borderline' two compartment modeling
When can drugs be successfully modeled as one-compartment drugs?
If the patient is not harmed by initially elevated drug concentration in the alpha phase and no drug samples are taken in the alpha phase
What is the term used for drugs that exhibit 'nonsignificant' two compartment modeling only after equilibrium with the deep tissue compartment is complete?
Non-significant two compartment drugs
What represents the distribution of drug from Vi into Vt in the two-compartment model?
Alpha phase
For drugs with significant two-compartment modeling, when are plasma samples obtained for pharmacokinetic modeling?
Alpha phase or distribution has been completed
Which drugs are generally referred to as non-significant two-compartment drugs?
Drugs that behave as though end organs are located in slowly equilibrating tissue compartment
In the context of drug modeling, what does it mean if a drug can be successfully modeled as a one-compartment drug?
The patient is not harmed by initially elevated drug conc. in alpha phase
What happens if plasma samples are obtained during the distribution phase for drugs with significant two-compartment modeling?
The actual trough concs will be lower than those predicted by one-compartment model
What is the significance of increased drug plasma concs during the alpha phase for non-significant two-compartment drugs?
The pharmacologic response will be much less than the plasma concs would indicate
What represents the distribution of drug from Vi into Vt for most drugs?
The alpha phase
When can drugs be considered to exhibit non-significant two-compartment modeling only?
When a one-compartment model is used for drugs that exhibit significant drug elimination in the alpha phase
What occurs for drugs that border on having significant two-compartment modeling?
The actual trough concs will be lower than those predicted by one-compartment model
What is the consequence of using a one-compartment model for drugs that exhibit significant drug elimination in the alpha phase?
The actual trough concs will be lower than those predicted by one-compartment model
When are two-compartment computer models available for therapeutic drug monitoring?
When care is taken to avoid obtaining samples in distribution phase
Study Notes
Pharmacokinetic Modeling and Two-Compartment Pharmacokinetics
- Drug elimination from the body involves a slower rate process after equilibrium is established
- Two-compartment model assumes no drug in the tissue compartment at time t = 0
- Tissue drug level peaks and then declines as the concentration gradient between compartments narrows
- Distribution phase may be missed if blood is sampled too late after drug administration
- Two-compartment model involves first order rate constants for drug transfer between central and peripheral compartments
- The apparent volume of distribution (V) is the sum of Vi and Vt
- Loading doses of drugs should be given slowly to account for drug distribution into tissue compartment
- Inaccurate prediction of target organ location in Vi or Vt can lead to therapeutic or toxic effects
- Guidelines for rates of drug administration are often based on clinical response receptors
- Potassium is an example of a drug that follows the principle of two-compartment modeling
- Plasma samples obtained before complete distribution cannot be used to predict drug effects
- Slow drug distribution into the tissue compartment can pose problems in accurate interpretation of drug concentrations
Test your understanding of pharmacokinetic modeling and two-compartment pharmacokinetics with this quiz. Explore concepts such as drug distribution, tissue compartment dynamics, rate constants, volume of distribution, and clinical implications.
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