Pharmacology Drug Absorption Quiz

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Questions and Answers

What is a consequence of drugs being bound to plasma proteins?

They become more easily metabolized.

They can cross biological membranes easily.

They enhance the therapeutic effects immediately.

They remain inactive and cannot be excreted. (correct)

Which of the following drugs is primarily stored in fat?

Tetracyclines

Phenylbutazone

Digitalis

Thiopental (correct)

How does protein binding facilitate drug distribution?

By making drugs more accessible to metabolizing enzymes.

By acting as a carrier for drugs insoluble in body fluids. (correct)

By increasing the concentration of free drug molecules.

By accelerating the excretion of the drugs.

In hypo-proteinemia, what adjustment should be made regarding drug dosing?

Lower the dose to avoid potential drug toxicity. Signup and view all the answers

What effect can occur when one protein-bound drug replaces another with a higher affinity?

Increased risk of toxicity from the displaced drug. Signup and view all the answers

What process moves molecules from low concentration to high concentration using energy?

Active transport Signup and view all the answers

Which factor does NOT influence the rate of drug absorption?

Presence of enzymes Signup and view all the answers

How does facilitated diffusion differ from passive transport?

It involves a carrier system Signup and view all the answers

Which of the following cell membrane components plays a role in passive transport?

Channels formed by proteins Signup and view all the answers

What is a primary example of active transport as mentioned in the content?

Sodium-potassium pump function Signup and view all the answers

What commonly helps non-lipid soluble drugs to penetrate the cell membrane?

Facilitated diffusion Signup and view all the answers

Which of the following is NOT a characteristic of the cell plasma membrane?

Three layers of lipid Signup and view all the answers

Which statement about diffusion is accurate?

It is a spontaneous process. Signup and view all the answers

Which factor does NOT affect drug absorption?

Patient's age Signup and view all the answers

What is the primary role of pinocytosis in drug transport?

Movement of large lipid-insoluble molecules Signup and view all the answers

Which of the following barriers is selectively permeable to certain drugs?

Blood brain barrier Signup and view all the answers

Which type of drug formulation is absorbed most rapidly?

Solutions Signup and view all the answers

What happens to a drug that is bounded to plasma proteins?

It may not be available for distribution Signup and view all the answers

Which of the following is NOT considered a physiological factor affecting drug distribution?

Technological advancements in drug formulation Signup and view all the answers

In which circumstance would drugs be most likely to pass the blood placental barrier?

When they are lipid-soluble Signup and view all the answers

What is the role of glial cells in the capillaries of certain organs?

To create physical barriers to drug penetration Signup and view all the answers

Study Notes

Drug Absorption

Drugs move across biological membranes through diffusion from an area of high concentration to low concentration.
The rate of diffusion is influenced by lipid solubility, size, degree of ionization, and the area of the absorptive surface.

Passage of Drug Across Cell Membranes

Physiochemical factors influencing drug movement:
- Drug molecule characteristics:
  - Molecular size and shape
  - Lipid solubility
- Cell membrane:
  - Composed of two layers of protein and a lipid center with pores.

Processes of Crossing the Cell Membrane

Passive transport:
- Movement of molecules through specific transport proteins down a concentration gradient.
- Does not require energy.
- Example: Glucose uptake by liver cells via GLUT4 transporter.
Active transport:
- Movement of molecules against a concentration gradient.
- Requires energy supplied by ATP breakdown.
- Example: Sodium-potassium pump in nerve cells.
Facilitated diffusion:
- Molecules move from a higher concentration to a lower concentration with assistance from a carrier.
- Non-lipid soluble drugs can cross the lipid matrix using carrier enzymes.
Pinocytosis:
- Movement of large lipid-insoluble molecules through endocytosis.
- Cell membranes envelop the substances into vesicles for transport.
- Energy-consuming process.

Factors Affecting Absorption

Drug-related factors:
- Physiochemical properties:
  - Lipid solubility
  - Degree of ionization
  - Molecular weight and valiancy
  - Chemical nature (organic or inorganic)
- Pharmaceutical form:
  - Solutions are absorbed faster than suspensions or powders (depending on particle size).
Patient/animal-related factors:
- Pathological condition of the absorbing surface
- Rate of general circulation
- Specific factors
- Route of drug administration

Drug Distribution

After absorption, drugs are distributed to various body compartments:
- Free in blood plasma
- Free in extracellular fluid
- Free in intracellular fluid
- Bound to plasma proteins
- Bound to tissue proteins
- Stored in fat depots
Distribution in extra or intracellular fluid depends on the pH gradient of the two fluids.
Some organs have barriers that restrict drug entry.
Blood barriers:
- Glial cells in capillaries of specific organs selectively permit certain drugs to pass.
- Blood-brain barrier (BBB) restricts passage to the CNS and CSF.
  - Quaternary ammonium compounds (e.g., neostigmine) cannot pass, while anesthetics can.
  - Drugs acting on the CNS must be able to cross the BBB.
- Blood-placental barrier restricts passage to the fetus.
  - May lead to resorption, abortion, malformation, or fetal depression.
  - Drugs for pregnant patients should not cross this barrier.
- Other barriers include intestinal, serous, and milk barriers.

Storage Depots

Plasma proteins:
- Albumin and other plasma proteins can bind to drug molecules.
- Bound drugs are inactive, not metabolized or excreted.
- Example: Phenylbutazone.
Extracellular depots:
- Connective tissue binds to ionic mucopolysaccharides.
- Hair, bones, and teeth can store heavy metals and tetracyclines.
Tissue proteins:
- Some drugs bind to tissue proteins more than plasma proteins.
- Example: Digitalis in cardiac muscle.
Fat:
- Important storage site for lipid-soluble drugs.
- Example: Thiopental.
Redistribution of drugs from the site of action to other sites (e.g., thiopental from brain to fat) terminates their effect.

Protein Binding

Specific affinity:
- Varies for different drugs and across animal species.
- May influence drug absorption, distribution, biotransformation, and excretion rates.
Reversible process:
- Bound drugs are inactive.
- Bound drugs cannot cross biological membranes, be metabolized, or be excreted.

Effects of Protein Binding on Drug Kinetics

Facilitation of absorption:
- Low concentration of free molecules.
Facilitation of distribution:
- Carrier for drugs insoluble in plasma.
- Example: Steroids.
Prolongation of drug action:
- Buffers drug concentration, slows metabolism or excretion.
Increasing initial doses:
- To achieve therapeutic dose of unbound drug.
Lowering the dose in hypoproteinemia:
- To avoid drug toxicity.
Drug interactions:
- Drugs with higher affinity can displace other protein-bound drugs, leading to toxicity.
- Example: Phenylbutazone with dicoumarol or salicylates with thyroxine.

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Description

Test your understanding of drug absorption processes and the factors influencing drug movement across cell membranes. This quiz covers key concepts such as passive and active transport mechanisms, and the physiochemical properties affecting drug diffusion.