Introduction to Pharmacokinetics

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Questions and Answers

What is the bioavailability percentage range for intramuscular (IM) administration?

5 to 30

75 to 100 (correct)

100

50 to 75

Which of the following routes has a defined bioavailability of 100%?

Rectal (PR)

Oral

Intravenous (IV) (correct)

Transdermal

What is a major reason large molecule drugs like insulin are typically given parenterally?

They are cheaper to produce

They are less effective when administered parenterally

They have high oral bioavailability

They have significantly lower bioavailability via non-parenteral routes (correct)

What is one factor that affects the oral bioavailability of a drug?

First-pass elimination Signup and view all the answers

Which physical characteristic of a drug can impede its absorption in the gastrointestinal tract?

Hydrophilicity and lipophilicity balance Signup and view all the answers

What does the term 'Cmax' refer to in pharmacokinetics?

The maximum concentration of a drug in plasma Signup and view all the answers

Which route of administration generally has the lowest bioavailability?

Oral (PO) Signup and view all the answers

In the context of oral drug absorption, what is the role of P-glycoprotein?

It serves as an efflux pump for drugs Signup and view all the answers

What does the term 'bioavailable fraction (F)' refer to?

The amount of drug that reaches systemic circulation Signup and view all the answers

What is the primary goal of drug therapy?

To achieve a desired beneficial effect with minimal adverse effects. Signup and view all the answers

Which processes are referred to as pharmacokinetics?

Absorption, distribution, metabolism, and excretion. Signup and view all the answers

What does the Henderson–Hasselbalch equation help to calculate?

Ionized and unionized forms of a drug. Signup and view all the answers

What is a key factor influencing the therapeutic range of a drug?

The oral bioavailability of the drug. Signup and view all the answers

In the context of drug therapy, what does 'individual variability' refer to?

Differences in drug response among individuals. Signup and view all the answers

What is meant by 'bioavailability' in pharmacokinetics?

The proportion of active drug that enters circulation when introduced into the body. Signup and view all the answers

What is the relationship between drug concentration and its effect, according to the principles of pharmacology?

The relationship can vary depending on the drug and individual. Signup and view all the answers

How does the gastrointestinal anatomy affect drug absorption?

Different sections of the gastrointestinal tract have variable absorption characteristics. Signup and view all the answers

What does the term 'pharmacodynamics' primarily concern?

The relationship between drug concentration and its effects on the body. Signup and view all the answers

Which factor can significantly influence a drug's oral bioavailability?

Gastric pH and gastrointestinal tract motility. Signup and view all the answers

What is the primary focus of pharmacokinetics in drug studies?

The study of how the body affects a drug's movement and concentration Signup and view all the answers

What does the term 'drug elimination' refer to?

The processes of drug metabolism and excretion Signup and view all the answers

Which factor does NOT influence the absorption of a drug?

The dose of the drug administered Signup and view all the answers

Which of the following describes the therapeutic range of a drug?

The concentration of a drug that avoids toxicity and ensures effectiveness Signup and view all the answers

What is the process of drug absorption primarily concerned with?

The transfer of a drug from its administration site to systemic circulation Signup and view all the answers

Which statement correctly differentiates pharmacodynamics from pharmacokinetics?

Pharmacodynamics examines drug effects on the body, while pharmacokinetics investigates how the body affects the drug Signup and view all the answers

What role do physiologic barriers play in drug delivery?

They restrict the access of drugs to their target organs Signup and view all the answers

Which of the following best describes the significance of understanding drug distribution?

It influences how drugs reach their target sites within the body Signup and view all the answers

Which parameter is most relevant to the pharmacokinetics of a drug administered intravenously?

Extent of absorption into the systemic circulation Signup and view all the answers

What is an essential outcome of the dose-response relationship in drug therapy?

Establishing the relationship between drug dose and its pharmacodynamics Signup and view all the answers

What is the primary factor that determines the extent of oral absorption of a drug?

Hydrophilicity and lipophilicity balance Signup and view all the answers

How does the P-glycoprotein efflux pump affect drug absorption?

It reduces the extent of absorption by expelling drugs from epithelial cells Signup and view all the answers

What is the first step in the pharmacokinetic process following oral administration of a drug?

Disintegration of the tablet/capsule Signup and view all the answers

Which of the following is not a component determining the rate of absorption of a drug?

Clinical effectiveness of the drug Signup and view all the answers

What does bioavailability measure in a pharmacokinetic context?

The fraction of unchanged drug reaching systemic circulation Signup and view all the answers

What does AUC stand for in the context of drug bioavailability?

Area Under the Curve Signup and view all the answers

Which route of administration is used as a reference for measuring bioavailability?

Intravenous (IV) administration Signup and view all the answers

Which characteristics define the therapeutic window of a drug?

Cmax and minimal toxic concentration Signup and view all the answers

Which part of the gastrointestinal tract is primarily responsible for drug absorption?

Small intestine Signup and view all the answers

Why is it important to differentiate between the rate and the extent of absorption?

They impact the drug's onset of action and bioavailability measurements Signup and view all the answers

What typically follows drug absorption in the pharmacokinetic process?

First pass through the liver Signup and view all the answers

How is the extent of absorption and bioavailability defined for non-IV routes?

By comparing them to IV administration Signup and view all the answers

Which of the following processes is NOT a part of drug absorption and metabolism?

Disintegration of food Signup and view all the answers

What is the area under the concentration-time curve (AUC) used to measure?

Extent of bioavailability for a drug Signup and view all the answers

What is true about the bioavailability (F) for the intravenous route?

F is equal to 1 Signup and view all the answers

Which of the following steps occurs after the metabolism in the GI tract?

Hepatic metabolism Signup and view all the answers

Study Notes

The Goal of Drug Therapy

The goal of drug therapy is to achieve a desired beneficial effect, such as curing a disease, with minimal adverse effects.
This requires a rational approach that combines pharmacodynamics and pharmacokinetics to understand the dose-effect relationship.
This includes selecting the appropriate drug and the right dose/dosing interval.

Individual Variations

Drug concentrations vary greatly among individuals, requiring personalized dosing.
This is due to factors such as genetics, physiology, and lifestyle.

Dose-Response Relationship

Describes the relationship between drug concentration and effect in the body.
Can be studied through pharmacokinetics and pharmacodynamics.
Pharmacokinetics studies how the body affects the drug, while pharmacodynamics studies how the drug affects the body.

Pharmacokinetics

Focuses on the time course of drug absorption, distribution, metabolism, and excretion (ADME).
All of these processes involve drug passage across cell membranes.
Drug disposition refers to the fate of a drug after absorption, including distribution, metabolism, and excretion.
Drug metabolism and excretion together are also called drug elimination.

Absorption

Defined as the movement of a drug from its site of administration to the systemic circulation.
Absorption depends on the physicochemical nature of the drug, drug formulation, route of administration, and patient's state.

The Henderson-Hasselbalch Equation

Useful for calculating the ionized and unionized forms of a drug at a given pH.
Helps understand drug absorption and distribution.

Gastric vs. Intestinal Absorption

Gastric absorption is generally slower due to lower pH and lower surface area compared to the intestines.
Intestinal absorption is more efficient due to higher pH and larger surface area.

Oral Administration

Involves several steps: disintegration of the tablet/capsule, dissolution of small particles, absorption in the GI tract, first-pass metabolism by the liver, drug distribution, urinary excretion, and hepatic metabolism.
Absorption primarily occurs in the small intestine.

Bioavailability (F)

The fraction of unchanged drug reaching the systemic circulation following administration by any route.
Measured by the area under the concentration-time curve (AUC).
The AUC following IV administration is used as the reference value.
For IV route, F = 1, as there is no absorption process involved.

Factors Affecting Oral Bioavailability

Physicochemical properties of the drug:
- A balance of hydrophilicity (water-loving) and lipophilicity (fat-loving) is needed for optimal absorption.
- Too high hydrophilicity prevents passage through the lipid cell membrane.
- Too high lipophilicity hinders dissolution in water.
Formulation:
- Has a major impact on bioavailability.
- Different formulations can lead to different absorption rates and extents.
First-pass elimination:
- Metabolism of the drug in the liver before it reaches systemic circulation.
- Reduces bioavailability.
P-glycoprotein efflux pump:
- Can actively transport drugs out of cells, limiting absorption.

Rate of Absorption

Determined by physicochemical properties of the drug, drug formulation, and route of administration.
Different from extent of absorption (bioavailability), measured by AUC.
Determines the onset of action of the drug.
Faster absorption leads to faster drug action.

Time Course of Drug Effect

The temporal characteristics of drug effect and its relationship to the therapeutic window.
The therapeutic window is the concentration range between minimal toxic concentration and minimal therapeutic concentration.
Key factors include:
- Lag time: Time delay from administration to onset of action.
- tmax: Time to reach peak concentration (Cmax).

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Description

This quiz explores the objectives of drug therapy, highlighting the significance of pharmacodynamics, pharmacokinetics, and the dose-response relationship. It also examines individual variations in drug responses and the importance of personalized dosing based on genetics and lifestyle factors.