Farmaco Flashcards
Final_Fully_Corrected_Questions_and_Answers_Table
Question
Answer
Define pharmacokinetics.
Pharmacokinetics describes the relationship between drug dose and drug concentration in plasma or, at the site of drug effect, over time. It can be thought of as “what the body does to the drug.” (33)
What are three fundamental processes that govern pharmacokinetics?
Three fundamental processes that govern pharmacokinetics are absorption, distribution, and elimination (metabolism and excretion). (33)
Define volume of distribution.
Volume of distribution refers to the distribution of an administered drug into various tissues throughout the body. (34)
What is a basic mathematical expression to describe volume of distribution?
This basic mathematical expression can be used to describe volume of distribution:
Volume of distribution = Amount of dose ÷ Concentration (34)
Does the transfer of a drug to peripheral tissues increase or decrease the drug’s total volume of distribution?
The transfer of a drug to peripheral tissues increases the drug’s total volume of distribution. The peripheral tissues can be thought of as peripheral volume. (34)
What are two properties of a drug that influence its distribution to peripheral tissues?
Two properties of a drug that influence its distribution to peripheral tissues are its solubility and drug binding. The more soluble a drug is, and the more it binds to peripheral tissues, the greater the total volume of distribution. (34)
Is the volume of distribution constant over time?
The volume of distribution is not constant over time, due to transfer of drug to the peripheral tissues (increases the total volume of distribution) and elimination (decreases the total volume of distribution). (35)
Define drug clearance.
Clearance is the rate of drug removal from the plasma. It is defined in units of flow, that is, the volume completely cleared of drug per unit of time (e.g., liters per minute). (35)
What is a basic mathematical expression to describe clearance?
This basic mathematical expression is used to describe clearance: Clearance = Q(Cin − Cout)/Cin. (37)
What is the difference between systemic clearance and intercompartmental clearance?
Clearance can be either systemic or intercompartmental. Systemic clearance is permanent drug removal from the body, whereas intercompartmental clearance is drug movement between plasma and peripheral tissues. (36)
What is drug elimination? How does drug elimination compare to drug clearance?
The drug elimination rate (mg/min) is the removal of drug in proportion to drug concentration. Clearance is drug elimination normalized to concentration. Drug elimination is high in the presence of high drug concentrations and low in the presence of low concentrations. Clearance is the same regardless of drug concentration. (36)
Define extraction ratio.
The extraction ratio is the fraction of inflowing drug extracted by an organ. (36-37)
What is a basic mathematical expression to describe extraction ratio?
A basic mathematical expression to describe extraction ratio (using Cin and Cout to represent the drug concentration moving into and out of an organ, respectively) is: (Cin − Cout)/Cin. (37)
When is the extraction of a drug “flow limited”?
The extraction of a drug by an organ is “flow limited” when the organ has a tremendous capacity to metabolize the drug and metabolism is limited only by the amount of blood flow to the organ. An example of this is the hepatic clearance of propofol, whose extraction ratio is nearly 1. (37)
When is the extraction of a drug “capacity limited”?
The extraction of a drug by an organ is “capacity limited” when the organ is limited in its capacity to take up and metabolize the drug. Clearance of the drug can be influenced by liver disease or enzymatic induction and is independent of blood flow to the organ. An example of this is the hepatic clearance of alfentanil, whose extraction ratio is very low. (37)
Define front-end kinetics.
Front-end kinetics describes intravenous drug behavior immediately following its administration. It accounts for how drug concentration changes over time as drug distributes throughout the circulatory system and into peripheral tissues following injection. (37)
What is a compartmental pharmacokinetic model?
A compartmental pharmacokinetic model is a schematic rendering or illustration of a complex exponential equation used to describe drug concentrations over time. There are several types; for example, there are pharmacokinetic models with one, two, or three compartments. The number of compartments reflects the complexity of the exponential equations. (38)
How are compartmental pharmacokinetic models created?
To create a compartmental pharmacokinetic model, a drug is administered and plasma drug concentrations are measured and charted immediately and at various points in time. Data from several individuals are collected. Using sophisticated modeling software, compartmental pharmacokinetic models are built that consist of parameters for a complex exponential equation. (38)
What are the three distinct phases of rate of drug concentration decline over time that are illustrated in the three-compartment model?
For many drugs, there are three distinct phases of rate of drug concentration decline: (1) The “rapid-distribution” phase (beginning immediately after intravenous bolus) when there is rapid movement of drug from the plasma to the rapidly equilibrating tissues. (2) The “slow-distribution” phase, when drug moves to the more slowly equilibrating tissues. (3) The “elimination” phase, drug returns from the tissues to the plasma and is permanently removed by metabolism or excretion. (38)
How are compartmental pharmacokinetic models used?
Compartmental pharmacokinetic models are used to explore drug concentrations over time for various drug doses. Some models have been used to program infusion pumps. Using special infusion pumps, practitioners enter a desired drug concentration and the model predicts how much drug is required to reach and maintain a target concentration. This technology is known as target-controlled infusions. (40-41)
Define back-end kinetics.
Back-end kinetics describes how plasma drug behaves during a continuous infusion and how concentrations decrease once the continuous infusion is terminated. (41)
Define decrement time and context-sensitive half-time.
Decrement time is the time required to reach a specified plasma concentration once an infusion is terminated. The context-sensitive half-time is the 50% decrement time. (41)
How does the duration of a continuous infusion of drug influence the drug’s decrement time?
During a continuous infusion, drug accumulates in peripheral tissues, prolonging the decrement time. The longer the infusion, the longer the decrement time. (41)
Define biophase.
Biophase refers to the time delay between changes in plasma concentration and drug effect. It accounts for the time required for drug to diffuse from the plasma to the site of action plus the time required, once the drug is at the site of action, to elicit a drug effect. (41)
Define pharmacodynamics.
Pharmacodynamics is the relationship between drug concentration and pharmacologic effect. It can be thought of as “what the drug does to the body.” (42)
What is a pharmacodynamic model?
A pharmacodynamic model describes the relationship between drug concentration (most frequently the effect site concentration) and drug effect. (42)
How is a pharmacodynamic model created?
To create a pharmacodynamic model, a specific drug effect (such as analgesia or loss of responsiveness) is measured at various drug concentrations. Data are combined from several individuals, and measured concentrations are plotted versus the observed effect. (43)
How is a pharmacodynamic model used?
A pharmacodynamic model is used to predict drug effects from measured or estimated concentrations. (43)
What is drug potency?
Drug potency describes the amount of drug required to elicit an effect, with C50 as a commonly utilized metric for the comparison of potency between drugs. (43)
What is drug efficacy?
Drug efficacy describes the effectiveness of a drug to elicit an action when attached to a receptor. Drugs that achieve maximal effect are known as full agonists, and those with an effect less than maximal are known as partial agonists. (44)
What is an anesthetic drug interaction?
Anesthetic drugs interact to enhance effects. Various effects have been characterized for interactions between inhaled agents and opioids, as well as sedatives and opioids. (45)
Distinguish among additive, antagonistic, and synergistic drug interactions.
Drug interactions can be additive, synergistic, or antagonistic. For additive drug interactions, when the drugs are coadministered their overall effect is the sum of the two individual drug effects. For synergistic drug interactions, administering both drugs leads to an effect greater than the sum of their individual effects. With antagonistic drug interactions, the overall drug effect is less than if the drug combination was additive. (45)
What are some examples of weight scalars, and how are they used clinically?
What are some examples of weight scalars, and how are they used clinically?
Examples of weight scalars include lean body mass, ideal body weight, and fat-free mass. Weight scalars are used to dose drugs administered to obese patients to avoid excessive or underdosing these patients. In general, the purpose of using weight scalars is to match dosing regimens for obese patients with what is required for patients of normal size. Several weight scalars have been used for anesthetic agents, each with advantages and limitations. The scientific foundation for weight scalars is relatively immature. Clinical trials are warranted to validate their use to improve dosing obese patients. (47)
Do volatile anesthetics accumulate more in obese patients than in lean patients, thus prolonging emergence in obese patients?
Do volatile anesthetics accumulate more in obese patients than in lean patients, thus prolonging emergence in obese patients?
Contrary to perception, volatile anesthetics do not accumulate more in obese patients than in lean patients, and emergence in obese patients has not been confirmed to be prolonged. Blood flow to adipose tissue decreases with increasing obesity. In addition, the time required to fill adipose tissue with enough volatile anesthetic to significantly prolong emergence is much longer than the duration of most anesthetics. (47-49)
How does age influence anesthetic dosing in the elderly?
How does age influence anesthetic dosing in the elderly?
Both pharmacokinetics and pharmacodynamics are altered with age. In the elderly, a decrease in cardiac output slows drug circulation time and decreases perfusion of metabolic organs. This results in higher peak plasma drug concentrations and decreased clearance for a given dose. Smaller doses of most anesthetic drugs are needed in elderly patients to produce the same therapeutic effect noted in younger counterparts based on pharmacokinetic and pharmacodynamic models. For example, to achieve an equipotent dose of remifentanil in an 80-year-old, the dose should be reduced by 55% of what would be administered to a 20-year-old. An analysis for propofol had similar results. The dose of propofol for an 80-year-old should be reduced by 65% of what would be administered to a 20-year-old for an equipotent effect. Dosing adjustments in elderly patients should account for their overall physical status (physiologic age) as well as their actual age. (50)
