Pharmacology: Pharmacokinetics and Drug Administration

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Questions and Answers

What is a primary characteristic of simple diffusion in passive transfer?

It involves active transport processes.

It uses energy from ATP.

It occurs along the concentration gradient. (correct)

It requires a carrier protein.

Which type of molecules generally pass across the lipid phase of the cell membrane during simple diffusion?

Ions

Large proteins

Polysaccharides

Lipid-soluble molecules (correct)

How do water and water-soluble small molecular weight drugs cross the cell membrane?

By endocytosis

Through the lipid phase

Using carrier proteins

Through water-filled pores (correct)

Which of the following is NOT a characteristic of simple diffusion in passive transfer?

Involves a carrier Signup and view all the answers

What is the primary driving force for simple diffusion?

A concentration gradient Signup and view all the answers

Which process is involved in what the body does to the drug and affects how the drug enters the bloodstream?

Absorption Signup and view all the answers

What is the term for the process of drug movement from the bloodstream to various tissues and organs in the body?

Distribution Signup and view all the answers

Which step in pharmacokinetics is primarily responsible for the chemical alteration of a drug in the body?

Metabolism Signup and view all the answers

Which pharmacokinetic process pertains to the removal of the drug from the body?

Excretion Signup and view all the answers

Why is it important to consider pharmacokinetics in designing the dose, route, and frequency of drug administration?

To ensure the drug achieves therapeutic levels without causing toxicity Signup and view all the answers

What is the main structural composition of the cell membrane?

Bimolecular lipid sheet Signup and view all the answers

Which of the following molecules interrupt the bimolecular lipid sheet in the cell membrane?

Protein macromolecules Signup and view all the answers

Through which of the following structures can ions primarily pass through the cell membrane?

Ion channel Signup and view all the answers

What other structure, besides the lipid bilayer, allows the passage of drugs through the cell membrane?

Water filled pores Signup and view all the answers

Which of these components is NOT a primary part of the cell membrane's composition related to drug passage?

Cytoskeleton Signup and view all the answers

What happens to the rate of passage across the membrane when the gradient of a drug increases?

It increases Signup and view all the answers

Which of the following statements is true about the molecular weight and size of a drug?

The smaller the size, the faster the rate of passage Signup and view all the answers

Which factor is essential for drug absorption?

Solubility in water Signup and view all the answers

Which factor improves a drug's absorption when its value is higher?

Oil/water partition coefficient Signup and view all the answers

The rate of passage across the membrane is primarily influenced by which of the following?

Gradient and molecular size Signup and view all the answers

What is the bioavailability of a drug administered intravenously (iv)?

100% Signup and view all the answers

Which of the following routes of administration is most variable in terms of bioavailability?

Oral Signup and view all the answers

How is bioavailability of a route other than iv generally calculated?

By comparing the area under the curve (AUC) of the route to the AUC of the iv route Signup and view all the answers

Which of these statements correctly defines bioavailability?

The proportion of a drug that reaches systemic circulation unchanged Signup and view all the answers

If the AUC of an orally administered drug is 50 and the AUC of the same drug administered intravenously is 100, what is the bioavailability of the oral drug?

50% Signup and view all the answers

Which of the following is a characteristic of filtration in pharmacology?

Occurs along hydrostatic and osmotic gradients Signup and view all the answers

What is the molecular weight (M.W) threshold for a drug to undergo filtration?

Less than 500 Signup and view all the answers

Which factor does NOT influence the filtration of drugs?

Carrier proteins Signup and view all the answers

Filtration in pharmacology does NOT require which of the following?

Both a and b Signup and view all the answers

Which of the following statements is true about the filtration process?

It involves the passage of drugs through capillary endothelium and glomeruli Signup and view all the answers

Which of the following processes is energy dependent?

Pinocytosis Signup and view all the answers

Which vitamin is absorbed through pinocytosis in the terminal ileum?

Vitamin B12 Signup and view all the answers

What is pinocytosis primarily responsible for in cellular processes?

Transport of water and dissolved substances Signup and view all the answers

In which part of the digestive system does absorption of vitamin B12 occur due to pinocytosis?

Terminal ileum Signup and view all the answers

Which factor is crucial for the absorption of vitamin B12 through pinocytosis?

Intrinsic factor Signup and view all the answers

Which characteristic distinguishes active transport from facilitated diffusion?

Involvement of energy and enzymes Signup and view all the answers

Which statement about facilitated diffusion is correct?

It needs a carrier and can involve saturation and competition. Signup and view all the answers

What is an example of active transport?

Na+/K+ pump activity Signup and view all the answers

Which process is described by the movement of substances along the concentration gradient without energy expenditure?

Facilitated diffusion Signup and view all the answers

What is a common feature of both facilitated diffusion and active transport?

Both require a carrier and can involve saturation and competition Signup and view all the answers

Which route of administration allows for the fastest drug absorption into systemic circulation?

intravenous (I.V) Signup and view all the answers

Which of the following absorption factors does NOT contribute to increased drug absorption?

presence of diarrhea Signup and view all the answers

Which absorbing surface is considered to have the greatest vascularity?

alveoli Signup and view all the answers

In terms of surface area, which of the following organs provides the largest area for drug absorption?

intestine Signup and view all the answers

Which state of health can negatively affect oral drug absorption?

diarrhea and malabsorption conditions Signup and view all the answers

What does pKa represent in the context of drug ionization?

The pH at which 50% of the drug is ionized Signup and view all the answers

According to the Henderson-Hasselbalch equation, how is pKa calculated for weak acid drugs?

pKa = pH + log (unionized form/ionized form) Signup and view all the answers

What is the relationship between ionization and lipid solubility?

Low ionization equals high lipid solubility Signup and view all the answers

What does the degree of ionization of a drug depend on?

pH of the medium and pKa of the drug Signup and view all the answers

According to the Henderson-Hasselbalch equation, how is pKa calculated for weak base drugs?

pKa = pH = log (ionized form/unionized form) Signup and view all the answers

Study Notes

Pharmacokinetics

The body's effect on the drug involves four processes: absorption, distribution, metabolism, and excretion, which are important to design proper dose, route, and frequency of administration and to determine drug bioavailability.

Bioavailability

Bioavailability is the fraction (%) of administered drug that reaches the systemic circulation in an unchanged form.
It is 100% after IV administration and most variable after oral administration.
Bioavailability of a route is calculated by dividing the area under the curve (AUC) of the route by the AUC of the IV route and multiplying by 100.

Types of Passages of Drugs

Passive Transfer

Simple diffusion: occurs mostly across the lipid phase of the cell membrane and involves water and water-soluble small molecular weight drugs passing through water-filled pores.
Characteristics: occurs along the concentration gradient, does not require a carrier, and requires no energy.
Factors affecting passage: concentration gradient, molecular weight and size, solubility in water, and oil/water partition coefficient.

Transmembrane Movement of Drugs

Cell membrane is composed of a bimolecular lipid sheet interrupted by protein macromolecules and water-filled pores.
Ionization of drugs depends on the pH of the medium and pKa of the drug, which affects lipid solubility and drug passage.

Filtration

Filtration is the passage of drugs through capillary endothelium and glomeruli.
Characteristics: occurs along hydrostatic and osmotic gradients, does not require a carrier, and requires no energy.
Factors affecting filtration: molecular weight (less than 500), lack of binding to plasma proteins, hydrostatic and osmotic gradient, and blood flow.

Special Transfer

Facilitated Diffusion

Facilitated diffusion occurs along the concentration gradient, requires a carrier, and requires no energy.
Characteristics: site for saturation and competition (interaction), e.g., glucose uptake.

Active Transport

Active transport occurs against the concentration gradient, requires a carrier, and requires energy and enzyme.
Characteristics: site for saturation and competition (interaction), e.g., Na+/K+ pump and renal tubular excretion of penicillins.

Pinocytosis

Pinocytosis is an energy-dependent process, e.g., absorption of vitamin B12 and intrinsic factor by the terminal ileum.

Absorption

Absorption is the transfer of drugs from their site of administration to the systemic circulation.
Factors affecting absorption:
- Patient-related factors:
  - Route of administration (I.V > I.M > S.O > oral)
  - Absorbing surface:
    - Vascularity (alveoli > skeletal muscle > S.C)
    - Surface area (alveoli > intestine > stomach)
    - State of health (diarrhea and mal-absorption decrease oral absorption)

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Description

This quiz covers the basics of pharmacokinetics, including what the body does to a drug, and the importance of pharmacokinetics in designing proper dose, route, and frequency of administration. It also touches on drug bioavailability.