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Which drug is mentioned as having a volume of distribution greater than the total body volume?
Which drug is mentioned as having a volume of distribution greater than the total body volume?
What is the primary reason haemodialysis is not effective for certain drugs mentioned?
What is the primary reason haemodialysis is not effective for certain drugs mentioned?
What role do plasma proteins play in the pharmacological activity of drugs?
What role do plasma proteins play in the pharmacological activity of drugs?
How might two drugs that bind to the same transporter proteins affect each other?
How might two drugs that bind to the same transporter proteins affect each other?
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Which body compartments can drugs distribute into based on their volume of distribution?
Which body compartments can drugs distribute into based on their volume of distribution?
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What is a significant factor affecting drug distribution in the body?
What is a significant factor affecting drug distribution in the body?
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Which of the following describes the volume of distribution?
Which of the following describes the volume of distribution?
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Which tissue is known to significantly affect drug distribution due to its storage capacity?
Which tissue is known to significantly affect drug distribution due to its storage capacity?
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What is the clinical significance of two drugs binding to the same transporter proteins?
What is the clinical significance of two drugs binding to the same transporter proteins?
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Which barrier does NOT typically affect drug distribution?
Which barrier does NOT typically affect drug distribution?
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How does the unbound portion of a drug in the plasma differ from the bound portion?
How does the unbound portion of a drug in the plasma differ from the bound portion?
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Which factor is NOT typically associated with influencing drug distribution in the body?
Which factor is NOT typically associated with influencing drug distribution in the body?
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When considering the distribution around the body, which compartment is important to recognize?
When considering the distribution around the body, which compartment is important to recognize?
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What does plasma protein binding primarily impact regarding drugs?
What does plasma protein binding primarily impact regarding drugs?
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Which plasma protein is most important for drug binding?
Which plasma protein is most important for drug binding?
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What influences the extent of plasma protein binding?
What influences the extent of plasma protein binding?
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Why can't drugs bound to plasma proteins exert pharmacological effects?
Why can't drugs bound to plasma proteins exert pharmacological effects?
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In which scenario could competition for plasma protein binding sites occur?
In which scenario could competition for plasma protein binding sites occur?
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How is plasma protein binding expressed?
How is plasma protein binding expressed?
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Which of the following drugs is likely to have a high percentage of plasma protein binding?
Which of the following drugs is likely to have a high percentage of plasma protein binding?
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Which type of drugs do alpha-1-acid glycoproteins typically bind?
Which type of drugs do alpha-1-acid glycoproteins typically bind?
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What primarily forms the blood-brain barrier (BBB)?
What primarily forms the blood-brain barrier (BBB)?
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Which type of molecules is most inhibited from penetrating the blood-brain barrier?
Which type of molecules is most inhibited from penetrating the blood-brain barrier?
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How does inflammation affect the blood-brain barrier?
How does inflammation affect the blood-brain barrier?
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Which condition is associated with an increased concentration of drugs in the cerebrospinal fluid (CSF)?
Which condition is associated with an increased concentration of drugs in the cerebrospinal fluid (CSF)?
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What factor does NOT impact drug transfer across the placenta?
What factor does NOT impact drug transfer across the placenta?
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Why are water-soluble and ionized drugs generally unable to cross the blood-brain barrier?
Why are water-soluble and ionized drugs generally unable to cross the blood-brain barrier?
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In which scenario is drug accumulation highest in the placenta?
In which scenario is drug accumulation highest in the placenta?
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What characterizes the capillary endothelial cells in the brain, contributing to the blood-brain barrier?
What characterizes the capillary endothelial cells in the brain, contributing to the blood-brain barrier?
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Which of the following statements about drug transport in the placenta is true?
Which of the following statements about drug transport in the placenta is true?
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What is a known therapeutic advantage of bisphosphonates?
What is a known therapeutic advantage of bisphosphonates?
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Why are tetracycline antibiotics contraindicated during pregnancy?
Why are tetracycline antibiotics contraindicated during pregnancy?
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Which drug has the highest volume of distribution (Vd) according to the provided data?
Which drug has the highest volume of distribution (Vd) according to the provided data?
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What phenomenon occurs due to the pH difference between fetal and maternal plasma?
What phenomenon occurs due to the pH difference between fetal and maternal plasma?
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Which characteristic of certain drugs makes them less effectively removed by haemodialysis?
Which characteristic of certain drugs makes them less effectively removed by haemodialysis?
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What effect does binding drugs into body fat have on their volume of distribution?
What effect does binding drugs into body fat have on their volume of distribution?
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Which of these drugs would likely accumulate in bone and serve as a slow release reservoir for toxins?
Which of these drugs would likely accumulate in bone and serve as a slow release reservoir for toxins?
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Study Notes
Pharmacokinetics
- Pharmacokinetics describes the movement of a drug in the body. It consists of absorption, distribution, metabolism, and excretion.
- Distribution refers to how drugs move from the systemic circulation to the site of action.
- Two factors are main contributors to drug distribution: plasma protein binding and tissue partitioning.
- When studying pharmacokinetics, we study the movement of drug into, through, and out of the body in terms of 4 main characteristics: ADME
- Absorption
- Distribution
- Metabolism
- Excretion
Plasma Protein Binding
- Many drugs circulate in the bloodstream bound to plasma proteins.
- This binding is reversible.
- The extent of binding depends on the affinity of a particular drug for protein-binding sites.
- Plasma protein binding (PPB) is expressed as a % of the plasma concentration.
- For example, Warfarin is 99% PPB, meaning 99% of Warfarin in plasma is bound to plasma proteins; the remaining 1% is unbound and free to bind to receptors and be eliminated.
Plasma Proteins
- Albumin is the most important protein for drug binding and binds acidic drugs, including warfarin, NSAIDs, and sulfonamides.
- ß-globulin and acid glycoproteins bind to basic drugs, such as quinine.
### Unbound Drug
- Unbound drug is free in plasma, can bind to receptors, exerts a pharmacological effect, diffuses into interstitial fluid and cells, can be metabolized, and can be filtered at the glomerulus and excreted.
Bound Drug
- Bound drug is bound to plasma proteins, cannot bind to receptors, can't exert a pharmacological effect, cannot move from the plasma compartment, cannot be metabolized, and cannot be filtered at the glomerulus and excreted.
Factors That Affect Plasma Protein Binding
- Concentration of free drug.
- Drug affinity for the binding sites.
- Based on whether the drug is acidic or basic.
- Concentration of plasma protein.
- Disease states.
- Drug-drug interactions due to competition for the same plasma protein binding sites.
Blood-Brain Barrier (BBB)
- The BBB is formed by tight junctions between the continuous layer of capillary endothelial cells, and glial cells that surround the capillaries.
- The BBB inhibits the penetration of polar and ionised molecules into brain neurons.
- This barrier limits access of many drugs to the central nervous system (CNS).
Alteration of the BBB
- Alteration to the permeability of the BBB can affect drug efficacy.
- This can be caused by conditions such as inflammation, bacterial meningitis, bradykinins, and treatment for brain tumors.
Placenta
- The placenta is a selective barrier that protects the foetus from harmful effects of drugs.
- Almost all drugs cross the placenta to a certain extent.
- Some drugs accumulate in the placenta at levels exceeding those in maternal plasma.
- Drug transfer across the placenta depends on:
- Lipid solubility.
- Extent of plasma binding.
- Degree of ionisation.
Bone
- Certain drugs can accumulate in bone by adsorption onto the bone crystal surface and incorporation into the crystal lattice.
- This includes tetracycline antibiotic, heavy metals (e.g., lead, radium), and bisphosphonates.
- Bone can be a reservoir for the slow release of toxic agents, allowing effects to persist long after exposure.
- For example, lead or radium can persist in the bone after exposure.
### Volume of Distribution
- The volume of distribution (Vd) refers to the apparent volume into which a drug is distributed.
- Vd is calculated by dividing the total amount of drug in the body by its plasma concentration.
- Drugs with lower Vd tend to be found primarily in the plasma, while drugs with higher Vd are more widely distributed throughout the body.
- Drugs with a Vd greater than the total body volume are not efficiently removed from the body by hemodialysis (blood filtration).
Volume of Distribution Calculation
- Heparin Vd = 0.07L/kg
- Warfarin Vd=0.14L/kg
- Aspirin Vd = 0.17L/kg
- Amoxicillin Vd = 0.3L/kg
- Valproic acid Vd 0.1 – 0.4L/kg
- Paracetamol Vd = 0.9L/kg
- Diazepam Vd = 0.8-1 L/kg
- Fluoxetine Vd = 20-42L/kg
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Description
This quiz covers essential concepts of pharmacokinetics, including drug absorption, distribution, metabolism, and excretion (ADME). It also highlights the role of plasma protein binding in drug circulation. Test your understanding of these fundamental topics in pharmacology.
