50 Questions
What is a primary characteristic of simple diffusion in passive transfer?
It occurs along the concentration gradient.
Which type of molecules generally pass across the lipid phase of the cell membrane during simple diffusion?
Lipid-soluble molecules
How do water and water-soluble small molecular weight drugs cross the cell membrane?
Through water-filled pores
Which of the following is NOT a characteristic of simple diffusion in passive transfer?
Involves a carrier
What is the primary driving force for simple diffusion?
A concentration gradient
Which process is involved in what the body does to the drug and affects how the drug enters the bloodstream?
Absorption
What is the term for the process of drug movement from the bloodstream to various tissues and organs in the body?
Distribution
Which step in pharmacokinetics is primarily responsible for the chemical alteration of a drug in the body?
Metabolism
Which pharmacokinetic process pertains to the removal of the drug from the body?
Excretion
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
What is the main structural composition of the cell membrane?
Bimolecular lipid sheet
Which of the following molecules interrupt the bimolecular lipid sheet in the cell membrane?
Protein macromolecules
Through which of the following structures can ions primarily pass through the cell membrane?
Ion channel
What other structure, besides the lipid bilayer, allows the passage of drugs through the cell membrane?
Water filled pores
Which of these components is NOT a primary part of the cell membrane's composition related to drug passage?
Cytoskeleton
What happens to the rate of passage across the membrane when the gradient of a drug increases?
It increases
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
Which factor is essential for drug absorption?
Solubility in water
Which factor improves a drug's absorption when its value is higher?
Oil/water partition coefficient
The rate of passage across the membrane is primarily influenced by which of the following?
Gradient and molecular size
What is the bioavailability of a drug administered intravenously (iv)?
100%
Which of the following routes of administration is most variable in terms of bioavailability?
Oral
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
Which of these statements correctly defines bioavailability?
The proportion of a drug that reaches systemic circulation unchanged
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%
Which of the following is a characteristic of filtration in pharmacology?
Occurs along hydrostatic and osmotic gradients
What is the molecular weight (M.W) threshold for a drug to undergo filtration?
Less than 500
Which factor does NOT influence the filtration of drugs?
Carrier proteins
Filtration in pharmacology does NOT require which of the following?
Both a and b
Which of the following statements is true about the filtration process?
It involves the passage of drugs through capillary endothelium and glomeruli
Which of the following processes is energy dependent?
Pinocytosis
Which vitamin is absorbed through pinocytosis in the terminal ileum?
Vitamin B12
What is pinocytosis primarily responsible for in cellular processes?
Transport of water and dissolved substances
In which part of the digestive system does absorption of vitamin B12 occur due to pinocytosis?
Terminal ileum
Which factor is crucial for the absorption of vitamin B12 through pinocytosis?
Intrinsic factor
Which characteristic distinguishes active transport from facilitated diffusion?
Involvement of energy and enzymes
Which statement about facilitated diffusion is correct?
It needs a carrier and can involve saturation and competition.
What is an example of active transport?
Na+/K+ pump activity
Which process is described by the movement of substances along the concentration gradient without energy expenditure?
Facilitated diffusion
What is a common feature of both facilitated diffusion and active transport?
Both require a carrier and can involve saturation and competition
Which route of administration allows for the fastest drug absorption into systemic circulation?
intravenous (I.V)
Which of the following absorption factors does NOT contribute to increased drug absorption?
presence of diarrhea
Which absorbing surface is considered to have the greatest vascularity?
alveoli
In terms of surface area, which of the following organs provides the largest area for drug absorption?
intestine
Which state of health can negatively affect oral drug absorption?
diarrhea and malabsorption conditions
What does pKa represent in the context of drug ionization?
The pH at which 50% of the drug is ionized
According to the Henderson-Hasselbalch equation, how is pKa calculated for weak acid drugs?
pKa = pH + log (unionized form/ionized form)
What is the relationship between ionization and lipid solubility?
Low ionization equals high lipid solubility
What does the degree of ionization of a drug depend on?
pH of the medium and pKa of the drug
According to the Henderson-Hasselbalch equation, how is pKa calculated for weak base drugs?
pKa = pH = log (ionized form/unionized form)
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)
- Patient-related factors:
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.
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