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Pharmacokinetics | Drug Absorption

Ninja Nerd・41 minutes read

Pharmacokinetics video emphasizes drug absorption mechanisms, factors influencing absorption, and importance of pH environments for weak acids and bases. Understanding bioavailability is crucial for drug effectiveness and treatment decisions, with IV administration ensuring 100% absorption compared to other routes affected by various factors.

Insights

  • Understanding the pH environment and weak acid form of drugs is crucial for clinicians to ensure maximum drug absorption, highlighting the importance of placing weak acids in acidic environments for optimal absorption.
  • Bioavailability is a critical factor in drug effectiveness, with IV administration providing 100% bioavailability by bypassing first-pass effects, while oral administration may result in lower bioavailability due to factors like solubility and enzymatic breakdown in the GI tract.

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Recent questions

  • What is pharmacokinetics?

    Pharmacokinetics is the study of drug absorption, distribution, metabolism, and excretion in the body.

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Summary

00:00

Drug Absorption: Routes and Mechanisms Explained

  • Pharmacokinetics is the focus of the video, with an emphasis on absorption of drugs.
  • Different routes of drug administration are discussed, including oral, rectal, injections, topical, intravenous, inhaled, buccal, and sublingual.
  • Absorption of drugs involves mechanisms like passive diffusion, facilitated diffusion, active transport, and endocytosis.
  • Factors affecting drug absorption include pH, blood flow changes, surface area, speed of GI tract movement, and P-glycoproteins.
  • Weak acids in drug form can disassociate into a proton and a conjugate base, with the weak acid form being more easily absorbed.
  • To enhance absorption of weak acids, they should be placed in an acidic environment, like the proximal duodenum.
  • The acidic environment increases the number of protons, shifting the reaction towards the nonpolar, easily absorbable form of the drug.
  • The stomach and proximal duodenum are highlighted as acidic environments where weak acids are best absorbed.
  • Understanding the pH environment and weak acid form of drugs is crucial for clinicians to ensure maximum drug absorption.
  • The video aims to provide comprehensive understanding of pharmacokinetics to aid in exam preparation and overall learning.

14:43

Factors Affecting Drug Absorption and Bioavailability

  • The nonpolar form and the polar charge form of drugs exist, with the nonpolar non-charge form being more easily absorbed.
  • To convert a drug from the polar charge form to the nonpolar form, the environment must be made acidic by increasing the number of protons.
  • Weak acids like aspirin are best absorbed in the proximal duodenum, while weak bases like amphetamines are better absorbed in the distal small intestine.
  • Weak bases disassociate into a polar form and a nonpolar form, with the nonpolar form being easily absorbed.
  • Shifting the reaction towards the nonpolar form requires an alkaline environment by decreasing the number of protons.
  • Good blood flow is crucial for drug absorption, with reduced blood flow in shock states leading to decreased absorption.
  • Diarrhea decreases drug absorption due to fast motility, while constipation increases absorption by providing more contact time.
  • Diseases like inflammatory bowel disease and celiac disease that reduce surface area decrease drug absorption.
  • P-glycoproteins can inhibit drug absorption by pushing the drug back into the gastrointestinal tract, leading to multi-drug resistance.
  • Bioavailability is the fraction of a drug that enters the systemic circulation, with IV administration having 100% bioavailability compared to other routes affected by various factors like pH, blood flow, and surface area.

28:42

Bioavailability: Key to Drug Administration Success

  • IV Administration involves determining the amount of a drug given intravenously versus orally, considering how much actually reaches the bloodstream.
  • When a drug is given IV, the full dosage enters the bloodstream, bypassing cell membranes and first-pass effects, ensuring 100% absorption.
  • In contrast, oral administration may result in only a portion of the drug being absorbed into the bloodstream, affecting bioavailability.
  • Bioavailability is the percentage of a drug that reaches systemic circulation; for example, if 50mg of a drug is absorbed orally but 100mg would reach circulation IV, the bioavailability is 50%.
  • Factors affecting bioavailability include solubility, with lipid-soluble drugs being more easily absorbed, and hydrophilic drugs facing decreased absorption.
  • Instability in the GI tract can affect drug absorption, as seen with penicillin G being destroyed by gastric acid, reducing bioavailability.
  • Enzymes in the GI tract can also impact drug effectiveness, as with proteases breaking down insulin, decreasing bioavailability.
  • The first-pass effect occurs when a drug taken orally passes through the liver, where a portion may be metabolized, reducing the amount reaching systemic circulation.
  • Understanding bioavailability is crucial for drug effectiveness; for instance, nitroglycerin is more effective sublingually to bypass first-pass metabolism.
  • When administering drugs, considering bioavailability is essential; IV administration ensures 100% bioavailability, making it ideal for critical situations like drug overdoses.

42:15

Pharmacokinetics: Absorption and Drug Distribution

  • Focus on pharmacokinetics, specifically absorption
  • Next part will cover drug distribution in pharmacokinetics
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