Pharmacology Chapter on Drug Absorption

Questions and Answers

What is the primary definition of absorption in drug pharmacokinetics?

The process of metabolism by the liver

The movement of drug from the site of administration into the blood circulation (correct)

The breakdown of drug into inactive forms

The elimination of drug from the body

What does bioavailability measure in drug absorption?

The amount of drug reaching systemic circulation in an unchanged form (correct)

The total volume of drug present in the body

The speed of absorption into the bloodstream

The extent of drug metabolism by the liver

What happens during first pass hepatic metabolism?

Drugs undergo complete chemical transformation by the intestines.

Drugs are partially metabolized by the liver before entering systemic circulation. (correct)

Drugs are eliminated completely before reaching the bloodstream.

Drugs are completely absorbed into the bloodstream.

Why are very hydrophilic drugs poorly absorbed?

They cannot cross lipid-rich cell membranes. Signup and view all the answers

Which drug property can negatively affect absorption due to pH instability?

Chemical instability Signup and view all the answers

What is the major site of drug absorption in the gastrointestinal tract?

Duodenum Signup and view all the answers

For optimal absorption, a drug should possess which of the following properties?

Moderate hydrophobicity with some aqueous solubility Signup and view all the answers

What is a significant outcome of the first pass metabolism on drug bioavailability?

Decreased amount of unchanged drug entering the systemic circulation Signup and view all the answers

What effect could large volumes of GI contents have on oral drug administration in ruminants?

Drug inactivation Signup and view all the answers

Which routes of administration are considered parenteral?

Subcutaneous (SC) and intravenous (IV) Signup and view all the answers

What is a potential adverse effect of parenteral drug administration in food animals?

Discoloration of the meat Signup and view all the answers

What type of drugs are almost completely absorbed through the skin?

Highly lipid-soluble drugs Signup and view all the answers

What factor is important for drug absorption from the respiratory tract?

Particle size Signup and view all the answers

Which of the following can impair drug absorption through the intradermal route?

Burns and skin disruptions Signup and view all the answers

What aspect can diminish drug absorption when administering parenterally?

Vasoconstriction due to certain procedures Signup and view all the answers

Which drug characteristics influence the rate of distribution to various compartments?

Lipid solubility, pH, and molecular size Signup and view all the answers

What role does the chemical structure of a drug play in its absorption?

It is important in attaching to the carrier molecule. Signup and view all the answers

How is pinocytosis primarily used in drug absorption?

For the uptake of polypeptides and bacterial toxins. Signup and view all the answers

Which drug is specifically mentioned as being actively transported into the renal tubule?

Penicillin Signup and view all the answers

What is a common characteristic of the IV route of drug administration?

It has the highest bioavailability of all routes. Signup and view all the answers

What factor does not significantly limit the absorption rate of drugs via the GI tract?

Blood flow. Signup and view all the answers

Which statement is true regarding the oral route of drug administration?

It generally has lower bioavailability than other routes. Signup and view all the answers

What can enhance the absorption of certain drugs when taken orally?

The presence of specific food types. Signup and view all the answers

Active transport mechanisms are characterized by which of the following?

They rely on specialized transport proteins and can be saturated. Signup and view all the answers

Which characteristic of drugs affects their ability to penetrate cell membranes?

Hydrophilic nature Signup and view all the answers

What type of drug is primarily bound to albumin?

Acidic drugs Signup and view all the answers

How does plasma protein binding affect the pharmacologic effect of a drug?

It slows the rate of reaching effective concentration Signup and view all the answers

What happens to drug bound to plasma proteins during kidney filtration?

It cannot be filtered Signup and view all the answers

What is a potential result of competition for binding sites on plasma proteins?

Increased free drug concentration Signup and view all the answers

Which drug characteristic enhances the likelihood of redistribution?

High lipid solubility Signup and view all the answers

What factor contributes to interspecies differences in drug distribution in animals?

Relative mass of the gastrointestinal tracts Signup and view all the answers

What typically terminates the action of a drug in the body?

Metabolism and excretion Signup and view all the answers

What is required for a drug to effectively cross the blood-brain barrier?

Lipophilic characteristics Signup and view all the answers

What process allows for the active transport of drugs from cerebrospinal fluid into the blood?

Active transport mechanisms Signup and view all the answers

Which of the following statements about cerebrospinal fluid is true?

It dilutes drug concentration as it circulates. Signup and view all the answers

How do drugs generally cross the placenta?

Simple diffusion Signup and view all the answers

What is the effect of inflammation of the brain on drug passage?

It can allow passage of certain drugs. Signup and view all the answers

Study Notes

Drug Absorption

Absorption involves the transfer of drugs from the administration site to blood circulation.
Rate and efficiency of absorption depend on the route of administration and dosage form.
Oral administration requires drug dissolution in gastrointestinal fluid and penetration of intestinal epithelial cells, primarily in the duodenum.
Understanding absorption rates is crucial for predicting the onset of drug action and response magnitude.

Bioavailability

Bioavailability is the fraction of the administered drug that reaches systemic circulation unchanged.
Example: If 100 mg of a drug is administered orally and 70 mg is absorbed, bioavailability is 70%.

Factors Influencing Drug Absorption

First Pass Metabolism:
- Drugs absorbed through the GI tract may be partially metabolized by the liver before reaching systemic circulation, reducing unchanged drug availability.
Solubility of the Drug:
- Poor absorption occurs in very hydrophilic or extremely hydrophobic drugs, as they cannot easily cross cell membranes.
Chemical Instability:
- Some drugs are unstable in gastric pH, leading to reduced absorption.
Active Transport:
- Requires specific chemical structures to utilize carrier molecules for drug absorption, as seen with anticancer drugs utilizing uracil transport systems.
Pinocytosis:
- Involves engulfing particles or liquids, important for certain polypeptides and immunoglobulins.

Route of Drug Administration

Different routes require different absorption processes.
Oral Route:
- Safest administration route but lower bioavailability due to first pass metabolism.
- Factors affecting absorption include gastric contents, blood flow, and GI tract differences across species.
Parenteral Route:
- Circumvents GI tract absorption; includes IV, IM, SC, and IP.
- Absorption affected by blood flow and vasoconstriction can impair it.
Skin/Intradermal Route:
- Highly lipid-soluble drugs are mostly absorbed; skin disruptions can impair absorption.
Respiratory Route:
- Used for gases and volatile anesthetics; particle size is critical for absorption.

Distribution of Drugs

Dose and Route of Administration:
- Impacts distribution; adequate blood flow is essential.
Blood Flow:
- Varies widely among tissues; higher flow in organs like the brain, liver, and kidneys.
Physicochemical Properties:
- Lipid solubility, pH, and molecular size significantly influence drug distribution.

Binding to Plasma Proteins

Only unbound drugs can cross cell membranes; plasma protein binding is reversible.
Acidic drugs primarily bind to albumin; basic drugs bind to α1-acid glycoprotein.
Binding may slow drug concentration achievement but does not prevent access to action sites.

Drug Interactions and Interspecies Differences

Drug Interactions:
- Occurs when two drugs compete for binding sites on plasma proteins, increasing free drug concentrations and effects.
Interspecies Differences:
- Variability in drug distribution is observed among different species, influenced by gastrointestinal tract mass.

Drug Redistribution

Redistribution from high blood flow sites to low can terminate drug action, especially for highly lipid-soluble drugs.

CNS and Transplacental Distribution

CNS Distribution:
- Limited by the blood-brain barrier, requiring high lipid solubility to pass.
- Active transport mechanisms exist for certain acids and bases in the choroid plexus, affecting CNS drug levels.
Transplacental Distribution:
- Drugs can cross the placenta via simple diffusion; the degree of transfer varies with drug properties.
Other Barriers:
- Tissues like the prostate and testicles possess barriers that limit drug concentration.

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Description

Explore the vital concepts of drug absorption and bioavailability in this quiz. Delve into factors that influence how drugs are absorbed into systemic circulation, including the impact of first-pass metabolism. Understanding these principles is essential for predicting drug action and efficacy.