Pharmacology: Drug Distribution and Binding

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Questions and Answers

What factor does NOT influence drug formulation and bioavailability?

Salt form

Disease state (correct)

Particle size

Crystal polymorphism

Which type of drug transport involves the movement of drugs based on their concentration gradient?

Active transport

Facilitated diffusion

Passive diffusion (correct)

Filtration

What is the significance of the blood-brain barrier in drug administration?

It is only penetrable by high molecular weight substances.

It allows all drugs to freely enter the brain.

It acts as a selective filter for drug absorption. (correct)

It prevents any substance from entering the brain.

Which process is exemplified by the reabsorption of glucose in the kidneys?

Facilitated diffusion Signup and view all the answers

How do membranes permit the passage of certain chemicals during filtration?

By controlling the drug's molecular size. Signup and view all the answers

What type of barrier must drugs overcome to enter the systemic circulation?

The skin barrier Signup and view all the answers

Which of the following statements about facilitated diffusion is accurate?

It uses selective carrier molecules for transport. Signup and view all the answers

What is a notable characteristic of passive diffusion?

It depends on the lipophilicity of the drug. Signup and view all the answers

What primarily affects the bioavailability of a drug?

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

Which statement about first pass hepatic metabolism is true?

It can decrease the amount of unchanged drug that reaches systemic circulation. Signup and view all the answers

What characteristic is essential for a drug to readily cross the Blood Brain Barrier (BBB)?

High lipid solubility Signup and view all the answers

Which factor is NOT influential in drug absorption?

Patient's weight Signup and view all the answers

For optimal absorption, a drug should ideally be:

Largely hydrophobic yet have some solubility in aqueous solutions Signup and view all the answers

What process allows for the movement of drugs from cerebrospinal fluid (CSF) into the blood?

Active transport mechanisms Signup and view all the answers

Which location is identified as the major site of drug absorption?

Duodenum Signup and view all the answers

Which of the following barriers can limit drug penetration and concentration in specific tissues?

Prostate barrier Signup and view all the answers

What consequence does chemical instability have on drug absorption?

Decreased bioavailability due to degradation Signup and view all the answers

How does cerebrospinal fluid help in maintaining low drug concentration in the CNS?

By circulating and diluting drug concentrations Signup and view all the answers

What is the primary mode of drug transfer across the placenta?

Simple diffusion Signup and view all the answers

Which of the following statements is true regarding hydrophilic and hydrophobic drugs?

Extremely hydrophobic drugs are poorly absorbed due to low solubility. Signup and view all the answers

Which situation would most likely reduce the extent of drug absorption?

Drug undergoing significant first pass metabolism Signup and view all the answers

Which statement about hydrophilic drugs is true?

Hydrophilic drugs do not readily penetrate cell membranes. Signup and view all the answers

What type of drugs primarily bind to albumin?

Acidic drugs Signup and view all the answers

What is the effect of drug-protein binding on pharmacologic effects?

Binding slows down the rate at which a drug reaches effective concentration. Signup and view all the answers

Which drug elimination process is limited by drug-protein binding?

Glomerular filtration Signup and view all the answers

What occurs when two drugs compete for the same plasma protein binding site?

The free drug concentration of one increases. Signup and view all the answers

What characterizes drugs that undergo redistribution to lower their action?

Highly lipid-soluble Signup and view all the answers

How does the gastrointestinal tract affect drug distribution in ruminant species?

It accounts for inter-species differences in drug distribution. Signup and view all the answers

Which factor limits the biologic response to a drug primarily?

Redistribution to the tissue Signup and view all the answers

What role does the chemical structure of a drug play in active transport?

It is essential for attachment to the carrier molecule. Signup and view all the answers

Which of the following drugs is NOT actively transported into a specific tissue or cell?

Glucose in skeletal muscle Signup and view all the answers

In which scenario might pinocytosis be particularly important for drug absorption?

Absorption of polypeptides and bacterial toxins Signup and view all the answers

Why does the oral route of drug administration generally have lower bioavailability?

First pass metabolism affects many drugs. Signup and view all the answers

What effect can the presence of food in the stomach have on drug absorption?

It can retard or enhance absorption depending on the type of food. Signup and view all the answers

Which route of administration places the drug directly into systemic circulation?

Intravenous (IV) Signup and view all the answers

What is a key characteristic of drug absorption through the intestinal route?

It requires no energy input. Signup and view all the answers

What common misconception exists regarding the effect of blood flow on gastrointestinal (GI) absorption?

Blood flow plays a minor role in GI absorption compared to other routes. Signup and view all the answers

Study Notes

Drug Absorption

Absorption is the process of drug movement from administration site to bloodstream.
The rate and efficiency of absorption vary by route and dosage form; oral route often has lower bioavailability due to first-pass metabolism.
The duodenum is the primary site for drug absorption, impacting onset and magnitude of drug action.

Factors Influencing Drug Absorption

Bioavailability: Amount of drug reaching systemic circulation unchanged; e.g., 100 mg administered with 70 mg absorbed results in 70% bioavailability.
First Pass Metabolism: Drugs absorbed via the GI tract may be partially metabolized by the liver, decreasing the amount reaching systemic circulation.
Solubility: Drugs must be hydrophobic yet also soluble in aqueous solutions for effective absorption; extreme hydrophilicity or hydrophobicity hinders absorption.
Chemical Instability: Some drugs are sensitive to gastric pH, affecting their stability and absorption (e.g., Penicillin G).
Drug Formulation: Factors like particle size, salt form, and excipients impact dissolution and thus absorption rate and bioavailability.

Drug Passage Across Membranes

Drugs must traverse various barriers to reach receptor sites, including the blood-brain barrier and epithelial barriers.
Passive Diffusion: Drug movement according to concentration gradient; influenced by lipid solubility and molecular size.
Filtration: Allows low molecular weight substances to cross membranes; demonstrated in kidney filtration.
Facilitated Diffusion: Less common; involves specific carriers to assist drug passage, such as glucose and vitamin B12 transport.
Active Transport: Involves specialized transport proteins; drugs can be actively absorbed against concentration gradients (e.g., iodine in the thyroid).
Pinocytosis: Minor absorption method for larger molecules and proteins; important in the gut for larger particles.

Route of Drug Administration

IV administration bypasses absorption process by placing drug directly into circulation.
Oral Administration: Although it is the safest method, it has lower bioavailability due to first-pass metabolism; influenced by factors like food presence and digestive differences across species.

Binding to Plasma Proteins

Only unbound drugs can cross cell membranes; binding is reversible and affects drug distribution and elimination.
Acidic drugs primarily bind to albumin while basic drugs bind to alpha-1-acid glycoprotein; this binding slows pharmacologic effect onset.
Drug-protein binding impacts elimination, particularly via glomerular filtration, as bound drugs cannot be filtered.

Drug Interactions

Competition for binding sites on plasma proteins can increase the amount of free drug, enhancing therapeutic or toxic responses.

Interspecies Differences

Variations in gastrointestinal tract mass among species affect interspecies drug distribution, particularly in veterinary pharmacology.

Drug Redistribution

Redistribution refers to drug sequestration in low blood flow tissues, terminating its action; often seen in highly lipid-soluble drugs like thiopental.

CNS Distribution

CNS drug distribution is limited by the blood-brain barrier, which consists of tight junctions in capillaries; drugs need high lipid solubility to cross.
Active transport systems in the choroid plexus regulate organic acid and base transport, maintaining low CNS concentrations of certain drugs.
Cerebrospinal fluid circulation continuously dilutes drug concentration in the CNS.

Transplacental Distribution

Drugs cross the placenta primarily through simple diffusion; CNS-affecting drugs generally possess properties enabling easy placental transfer.

Barriers in Other Tissues

Specific tissues such as the prostate, testicles, and eye have barriers that limit drug penetration, influencing drug concentration in those areas.

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Description

This quiz explores the key concepts related to drug distribution, focusing on hydrophilic drugs, their ability to penetrate cell membranes, and the significance of plasma protein binding. Understand the differences in binding for acidic and basic drugs and how these concepts impact drug efficacy.