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What does pharmacokinetics primarily refer to?
What does pharmacokinetics primarily refer to?
Which of the following pharmacokinetic properties involves the transfer of a drug from the site of administration into plasma?
Which of the following pharmacokinetic properties involves the transfer of a drug from the site of administration into plasma?
What is the primary mechanism through which 99% of drugs are absorbed?
What is the primary mechanism through which 99% of drugs are absorbed?
What does a higher bioavailability generally indicate about a drug's administration?
What does a higher bioavailability generally indicate about a drug's administration?
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Which pharmacokinetic process involves biotransformation primarily by the liver?
Which pharmacokinetic process involves biotransformation primarily by the liver?
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Which route of drug administration typically results in 100% bioavailability?
Which route of drug administration typically results in 100% bioavailability?
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Which factor does NOT influence the rate and extent of drug absorption?
Which factor does NOT influence the rate and extent of drug absorption?
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What happens to drugs administered through routes other than intravenous?
What happens to drugs administered through routes other than intravenous?
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What is the condition for a weak acid to cross the cell membrane effectively?
What is the condition for a weak acid to cross the cell membrane effectively?
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How does pH influence the absorption of weak acids and bases?
How does pH influence the absorption of weak acids and bases?
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Which of the following statements about ionization constants (pKa) is true?
Which of the following statements about ionization constants (pKa) is true?
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Which statement best describes the form of a weak base that is able to penetrate the cell membrane?
Which statement best describes the form of a weak base that is able to penetrate the cell membrane?
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What characteristic makes lipid-soluble drugs able to cross cell membranes?
What characteristic makes lipid-soluble drugs able to cross cell membranes?
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How does the redistribution equilibrium of a drug occur in the body?
How does the redistribution equilibrium of a drug occur in the body?
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What is the consequence of a drug being ionized?
What is the consequence of a drug being ionized?
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What determines the effective concentration of a drug at its absorption site?
What determines the effective concentration of a drug at its absorption site?
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What is the main characteristic of facilitated diffusion?
What is the main characteristic of facilitated diffusion?
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Which process is used to transport large drugs across the cell membrane?
Which process is used to transport large drugs across the cell membrane?
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What role does ATP play in active transport?
What role does ATP play in active transport?
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Which factor does NOT influence drug absorption?
Which factor does NOT influence drug absorption?
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Why might facilitated diffusion be inhibited?
Why might facilitated diffusion be inhibited?
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What is true about the ionization of most drugs?
What is true about the ionization of most drugs?
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Exocytosis is primarily responsible for which of the following?
Exocytosis is primarily responsible for which of the following?
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Which statement about lipid-soluble drugs is correct?
Which statement about lipid-soluble drugs is correct?
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What is the effect of a lower pKa value on a drug's acidity?
What is the effect of a lower pKa value on a drug's acidity?
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How does the pH of the stomach affect the absorption of aspirin?
How does the pH of the stomach affect the absorption of aspirin?
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In which pH environment is aspirin poorly absorbed?
In which pH environment is aspirin poorly absorbed?
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What happens to aspirin in the gastric cells when pH rises to 7.4?
What happens to aspirin in the gastric cells when pH rises to 7.4?
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How can alkaline agents like sodium bicarbonate be used in relation to aspirin toxicity?
How can alkaline agents like sodium bicarbonate be used in relation to aspirin toxicity?
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Why is it important to know the pKa of drugs in clinical settings?
Why is it important to know the pKa of drugs in clinical settings?
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What effect does blood flow have on drug absorption in the intestines compared to the stomach?
What effect does blood flow have on drug absorption in the intestines compared to the stomach?
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What general principle can be inferred about drug absorption based on the pH of the environment?
What general principle can be inferred about drug absorption based on the pH of the environment?
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Study Notes
Pharmacokinetics
- Pharmacokinetics describes what the body does to a drug, pharmacodynamics describes what the drug does to the body.
- Four properties impact the effectiveness of a drug:
- Absorption
- Distribution
- Metabolism
- Elimination
- These properties together are known as ADME.
- Absorption is the movement of a drug from its administration site to the bloodstream.
- Distribution involves the drug leaving the bloodstream and moving to interstitial and intracellular fluids.
- Metabolism is the process of the drug being biotransformed by the liver or other tissues.
- Elimination is the removal of the drug and its metabolites from the body via urine, bile, or feces.
Absorption
- The rate and extent of absorption depend on the environment where the drug is absorbed, chemical properties of the drug, and route of administration.
- Intravenous injection delivers the drug directly to the bloodstream, resulting in 100% bioavailability.
- Other routes of administration may result in partial absorption and lower bioavailability.
Mechanisms of Absorption from the GI Tract
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Passive Diffusion: the most common mechanism (~99% of drugs).
- Drugs move from high to low concentration.
- It's not carrier-mediated and does not require energy.
- Water-soluble drugs penetrate through aqueous channels, lipid-soluble drugs readily move through lipid bilayers.
- Facilitated Diffusion: carrier protein mediated, allowing the passage of large molecules through membranes, does not require energy.
- Active Transport: energy-dependent (ATP hydrolysis), moves drugs against a concentration gradient, has saturation kinetics, and can be competitively inhibited by other molecules.
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Endocytosis and Exocytosis: Processes for transporting larger-sized molecules across cell membranes.
- Endocytosis: engulfment and transport into the cell.
- Exocytosis: the reverse of endocytosis.
- Vitamin B12 is transported via endocytosis, neurotransmitters (norepinephrine) are released by exocytosis.
Factors Influencing Absorption
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pH Effect on Drug Absorption:
- Most drugs are weak acids or weak bases.
- Drugs pass through membranes more readily in their uncharged form.
- The ratio of charged to uncharged forms is determined by the pKa of the drug and pH of the environment.
- For weak acids: uncharged HA form permeates membranes readily, while the charged A− does not.
- For weak bases: uncharged B form permeates readily, while charged BH+ does not.
- Aspirin is an acidic drug with a pKa of 3.5.
- In the stomach (pH=1.5), aspirin is mainly uncharged (HA) and absorbed efficiently (~99%).
- In the small intestine (pH=8.5), aspirin is mostly charged (A-) and poorly absorbed (~1%).
- Aspirin is prone to causing peptic ulcers due to its high absorption in the acidic stomach environment and trapping of ionized aspirin in gastric cells.
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Clinical Significance of pKa:
- Determines absorption site.
- Used to treat drug toxicity: e.g., alkalinizing agents (sodium bicarbonate) increase the ionization of acidic drugs, promoting elimination.
- In breastfeeding: alkaline drugs may be well absorbed by the mother, but may not readily pass into breast milk due to ionization.
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Blood Flow:
- Intestines receive higher blood flow than the stomach, resulting in greater absorption.
- Shock can severely reduce blood flow to subcutaneous tissues, decreasing absorption from subcutaneous administration.
Other Factors
- Surface Area: Larger surface area increases absorption.
- Time: Drug absorption requires sufficient time for adequate transfer.
- P-glycoprotein: A protein involved in drug efflux, can reduce drug absorption.
- Lipid Solubility: Lipid-soluble drugs permeate cell membranes easily.
- Ionization: Ionized drugs are less permeable across membranes.
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Description
This quiz explores the fundamental concepts of pharmacokinetics, including the ADME properties: Absorption, Distribution, Metabolism, and Elimination. Understand how these properties affect drug effectiveness and the processes involved in each stage. Test your knowledge on the factors influencing drug absorption and the significance of different administration routes.
