Pharmacokinetics and Drug Absorption Process Quiz

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20 Questions

What is the main factor that determines the rate of drug absorption?

Total surface area

Which mechanism involves the use of energy (ATP) to transport large hydrophilic drugs during absorption?

Active transport

What type of environment do weak bases require for absorption?

Alkaline

How does IV administration affect bioavailability compared to oral administration?

Increases bioavailability

Which type of drugs have difficulty crossing cell membranes?

Hydrophilic drugs

How does hydrochloric acid in the stomach affect the oral absorption of penicillin G?

Decreases absorption

What is the role of P-glycoproteins in the small intestine regarding drug absorption?

Actively pump drugs out of cells

In pharmacokinetics, what does bioavailability refer to?

The amount of drug that reaches the bloodstream

For a weak basic drug with a pKa of 7.8, where does absorption occur best?

Jejunum in a basic solution

Why is understanding bioavailability crucial in drug development and administration?

To determine the amount of drug reaching systemic circulation

Which type of drugs are weak acids likely to have difficulty crossing cell membranes?

Hydrophilic drugs

How does bulk transport differ from facilitated diffusion in drug absorption?

Facilitated diffusion involves endocytosis while bulk transport uses receptors

What impact does decreased blood flow have on the absorption of drugs?

Reduces absorption

Why does IV administration ensure 100% bioavailability compared to oral administration?

IV drugs bypass first-pass metabolism which oral drugs undergo

What is the main reason for the lower bioavailability of hydrophilic or large, polar drugs?

They are actively pumped out of the cells by P-glycoproteins

Why is insulin, a large hydrophilic protein, associated with reduced bioavailability?

It is broken down by proteases in the GI tract

In drug overdose cases, why is the intravenous (IV) route preferred for administering an antidote?

To bypass the first-pass effect and increase bioavailability

How do P-glycoproteins in the small intestine affect drug absorption?

They pump drugs out of the cells back into the gut

Why is understanding absorption crucial in pharmacokinetics?

To maximize drug bioavailability for therapeutic effect

Where does absorption occur best for weak basic drugs with a pKa of 7.8?

In the distal ilium

Study Notes

  • Pharmacokinetics discussed in the video, focusing on absorption as the first process
  • Absorption is the drug reaching the bloodstream after administration
  • Common routes of administration include PO (oral), rectal, injections (subcutaneous, intramuscular, intradermal, intravenous), and inhalation
  • Passive diffusion and facilitated diffusion are mechanisms for absorption based on drug size and solubility
  • Active transport is used for large hydrophilic drugs, requiring energy (ATP)
  • Bulk transport is an alternative method for transporting large molecules using receptors and endocytosis
  • pH, blood flow, surface area, and P-glycoproteins can impact absorption
  • Weak acids require an acidic environment for absorption, weak bases require an alkaline environment
  • Blood flow is necessary for effective absorption, decreased blood flow can lead to decreased absorption.- Absorption of drugs depends on various factors including pH, blood flow, total surface area, contact time, and P-glycoproteins.
  • Route of administration (IV vs. oral) affects bioavailability, which is the fraction of drug that enters into the systemic circulation.
  • IV administration ensures 100% bioavailability as the drug goes directly into the bloodstream without passing through any membranes.
  • Oral administration, on the other hand, may result in lower bioavailability due to factors like solubility, instability, and first-pass metabolism.
  • Hydrophobic or small, non-polar drugs are easily absorbed due to their ability to cross cell membranes.
  • Hydrophilic or large, polar drugs have difficulty crossing cell membranes and thus have lower bioavailability.
  • Instability of the drug in the environment where it is administered can affect its absorption and bioavailability.
  • For example, penicillin G is not well-absorbed orally as it gets destroyed by hydrochloric acid in the stomach.
  • Insulin, a large hydrophilic protein, also experiences reduced bioavailability due to proteases that break it down in the GI tract.
  • P-glycoproteins in the small intestine can inhibit drug absorption by actively pumping them out of the cells and back into the gut.
  • This results in a decrease in bioavailability for drugs that are substrates for P-glycoproteins.
  • Understanding bioavailability is crucial in drug development and administration as it affects the amount of drug that reaches the systemic circulation and ultimately, its efficacy.
  • Nitroglycerin, for instance, can be given sublingually or intravenously to bypass the first-pass effect and increase its bioavailability.- An 18-year-old female was brought to the emergency department due to a drug overdose.
  • When administering an antidote, the ideal route is intravenous (IV) for maximum bioavailability, ensuring the whole dose reaches the systemic circulation.
  • In the case of a weak basic drug with a pKa of 7.8, absorption occurs best in the distal ilium in an alkaline environment due to the Chatelier principle, where fewer protons in the solution allow for a shift to the right in the reaction and the formation of more nonpolar molecules for easy absorption.
  • The jejunum, being the most basic solution and closest in pH to the drug's pKa, is the best site for absorption of weak bases.
  • Understanding the absorption process is crucial in pharmacokinetics, as it determines the amount of drug that reaches the systemic circulation for therapeutic effect.

Test your knowledge on pharmacokinetics, focusing on the absorption process of drugs into the bloodstream. Learn about mechanisms like passive diffusion, facilitated diffusion, active transport, and factors affecting absorption such as pH, blood flow, and bioavailability.

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