Pharmacology 2 absorbtion

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Questions and Answers

What is indicated by the ratio F in pharmacokinetics?

The rate of drug absorption

The bioavailability of a drug (correct)

The extent of drug metabolism

The dosage form of a medication

Which factor would enhance the bioavailability of a drug administered orally?

Higher dosage form particle size

Increased lipid solubility of the drug (correct)

Lower local blood flow at the site of administration

Higher molecular weight of the drug

Which drug characteristic would most likely result in slower absorption when administered orally?

Liquid dosage form

High local blood flow

Large molecular size (correct)

High lipid solubility

What is commonly true about the absorption of weak acids in comparison to weak bases?

Weak acids are typically absorbed faster than weak bases in acidic environments. Signup and view all the answers

When comparing intravenous (IV) administration of a drug to oral (p.o.) administration, what is a major consideration?

Oral doses may need to be significantly larger than their IV counterparts. Signup and view all the answers

What is the primary effect of macrolide antibiotics on Pgp substrates?

They enhance the absorption of Pgp substrates. Signup and view all the answers

Which route of administration avoids the absorption process entirely?

Intravenous administration Signup and view all the answers

Which factor does NOT improve absorption via the oral route?

Large particle size Signup and view all the answers

What type of administration makes systemic absorption less effective when topical effects are required?

Topical administration Signup and view all the answers

What characteristic of drugs enhances absorption through the topical route?

Higher lipophilicity Signup and view all the answers

What does a Volume of Distribution (Vd) value greater than total body fluids indicate?

The drug is extensively distributed throughout the body Signup and view all the answers

In a 70 kg adult, what is the approximate plasma volume?

3.5 L Signup and view all the answers

Which situation is likely to cause a decrease in Volume of Distribution?

Severe dehydration Signup and view all the answers

What is the typical Volume of Distribution for total body fluids in a 70 kg adult?

42 L Signup and view all the answers

What does a Vd equal to plasma volume suggest about a drug's distribution?

The drug remains in the plasma Signup and view all the answers

Which factor does NOT typically influence the Volume of Distribution?

Dietary habits Signup and view all the answers

How is Volume of Distribution expressed per kg in a 70 kg adult?

0.6 L/kg Signup and view all the answers

A condition that leads to selective distribution of a drug would most likely occur under which circumstance?

Selective tissue binding Signup and view all the answers

What is a primary characteristic of body depots for drug storage?

They are tissues where drugs are stored and released slowly. Signup and view all the answers

Which type of drugs can easily cross the Blood-Brain Barrier?

Small and lipid-soluble drugs. Signup and view all the answers

How does the Blood-CSF Barrier impact drug permeability?

Certain drugs may cross, but are often transported back by P-glycoprotein. Signup and view all the answers

What is a possible outcome of diuretic therapy regarding plasma levels?

It can lead to elevated plasma levels due to dilution. Signup and view all the answers

Depot injections are typically used for which purpose?

Sustained release of medication over time. Signup and view all the answers

Which factor is NOT typically a barrier to drug diffusion?

Muscle Tissue Permeability. Signup and view all the answers

What role do depot tissues play in pharmacokinetics?

They store drugs for constant release into the blood. Signup and view all the answers

When considering drug administration, which barrier is crucial for CNS-targeting drugs?

Blood-Brain Barrier. Signup and view all the answers

What is pharmacokinetics concerned with?

The movement and processing of drugs in the body Signup and view all the answers

Absorption of drugs primarily occurs through which mechanism?

Passive diffusion Signup and view all the answers

What does bioavailability measure?

The rate and extent of drug absorption Signup and view all the answers

Which route of administration generally does NOT rely on absorption?

Intravenous (IV) Signup and view all the answers

What aspect is NOT a part of the absorption process?

Vascular resistance Signup and view all the answers

In drug absorption, pinocytosis and phagocytosis are examples of what type of mechanisms?

Receptor-mediated transport Signup and view all the answers

Which of the following involves filtration in the drug absorption process?

Size exclusion based on molecular weight Signup and view all the answers

Which statement about the permeation of drugs across membranes is incorrect?

Large charged molecules preferentially use passive diffusion Signup and view all the answers

Study Notes

General Pharmacology Overview

Pharmacology involves the study of drugs and their effects on biological systems.
Key branches include pharmacokinetics (drug absorption, distribution, metabolism, excretion) and pharmacodynamics (drug action).

Pharmacokinetics

Defined as "What a Body Does to the Drug."
Focuses on absorption, distribution, metabolism, and elimination.

Absorption of Drugs

Movement of drugs from the site of administration to systemic circulation.
Main routes: oral, intravenous (IV), subcutaneous (SC), and intramuscular (IM).
Mechanisms of absorption involve passive diffusion, active transport, facilitated diffusion, and endocytosis.

Bioavailability

Bioavailability (F) indicates the rate and extent a drug is absorbed into circulation.
IV medications have 100% bioavailability (F = 1); oral medications may require larger doses due to lower F.

Factors Affecting Bioavailability

Drug absorption, gut wall metabolism, and hepatic first-pass effect can lower effective drug concentration.
Drugs with high lipid solubility (e.g., anesthetics) diffuse rapidly across cell membranes.
Local blood flow enhances absorption; e.g., intestines have greater blood flow than the stomach.
Molecular size and drug formulation impact absorption rate (solutions > suspensions > tablets).

Drug Ionization and pH

Drug ionization affects absorption; weak acids and bases demonstrate variable absorption based on pH.
Overexpression of P-glycoprotein (Pgp) in certain tumors can lead to multi-drug resistance.

Administration Routes

Systemic Routes: Enteral (oral, rectal), parenteral (IV, SC, IM).
- Oral absorption is favored when drugs are lipid-soluble and the stomach is empty.
- Parenteral routes (IV, SC, IM) avoid absorption issues and enable faster action.
Local Routes: Topical, inhalational, intranasal, conjunctival.
- Systemic absorption from topical applications is influenced by drug lipophilicity and skin condition.

Volume of Distribution (Vd)

Vd indicates how extensively a drug disperses in body fluids.
Plasma volume is approximately 3.5-4.5 L; total body water is around 40 L.
Conditions like congestive heart failure may alter drug distribution and concentrations.

Drug Depots and Barriers

Depots are body compartments for slow drug release (e.g., fat stores lipophilic drugs).
Barriers limit drug diffusion, including:
- Blood-Brain Barrier: Lipid-soluble drugs cross easily.
- Blood-CSF Barrier: Water-soluble and larger drugs cross with difficulty.
- Placental Barrier: Influences drug transfer during pregnancy.

Considerations for Drug Administration

Route of administration is critical for drugs intended to target specific sites, especially when crossing biological barriers.

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Description

Test your knowledge on drug bioavailability, its definition, and the factors affecting it. This quiz explores the concepts of rate and extent of absorption, and how they impact drug administration methods. Gain insights into why certain drugs may need higher oral doses due to low bioavailability.