NURS 1060: Drug Absorption Concepts Exam 1

Absorption of Drugs

• Critical thinking and clinical reasoning are essential for accurate and safe medication administration.
• Clinical Decision Making involves analyzing patient problems to prioritize responses, minimizing adverse changes in patient conditions.

Pharmacokinetics Overview

• Pharmacokinetics studies drug movement through four main processes:
  • Absorption: Drug moves from administration site into the bloodstream.
  • Distribution: Drug travels from blood to action or storage sites.
  • Metabolism: Drug undergoes enzymatic breakdown into metabolites.
  • Excretion: Removal of drug or metabolites from the body.

Drug Administration Routes

• Enteral: Absorption occurs in the gastrointestinal (GI) tract (e.g., oral, sublingual, rectal).
• Parenteral: More direct methods bypassing the GI tract (e.g., intravenous (IV), intramuscular (IM), subcutaneous (SubQ)).

Drug Absorption Process

• Oral drug absorption requires disintegration (tablet breaking apart) and dissolution (mixing with stomach fluids).
• Most drugs utilize passive diffusion for absorption, moving from high to low concentration areas.

Factors Influencing Drug Absorption

• Rate of dissolution varies by drug.
• Surface area: Larger surface area in the intestine facilitates faster absorption compared to the stomach.
• Blood flow: Higher blood flow areas enable more rapid absorption.

Drug Passage Mechanisms

• Drugs can cross membranes via:
  • Direct diffusion: Requires lipid solubility.
  • Channels and pores: Very few drugs can use this method.
  • Transport systems: Includes P-glycoprotein, which transports drugs out of cells, limiting absorption.

Role of P-Glycoprotein

• Acts as an anti-absorption transporter in organs such as:
  • Liver: Transports drugs into bile for elimination.
  • Kidney: Moves drugs into urine.
  • Intestine: Transfers drugs from blood into intestinal lumen.
  • Brain: Limits drug access to the brain.

Ionization and Drug Solubility

• The ionization state of drugs affects their solubility:
  • Acidic drugs tend to ionize in basic (alkaline) environments while basic drugs ionize in acidic environments.
  • Non-ionized forms are lipid-soluble and can diffuse across membranes.

Ion Trapping (pH Partitioning)

• Accumulation of drugs occurs based on pH differing across membranes:
  • Acid drugs accumulate in basic environments and vice versa.
• Example:
  • Aspirin (acid) in the stomach (pH 1) is non-ionized and lipid-soluble, allowing absorption into the bloodstream.

Blood-Brain Barrier Considerations

• Tight junctions in CNS capillaries restrict drug passage; only lipid-soluble drugs can penetrate.

Summary of Absorption Mechanism

• Oral absorption involves drug movement from the GI tract into the bloodstream, passing through the liver before entering systemic circulation.
• Overall absorption rate affects drug onset and intensity of effects.

Lipid-solubility in Pharmacology

• Lipid-solubility signifies a drug's capability to dissolve in fats, influencing its ability to traverse cell membranes.
• Drugs with high lipid-solubility are more proficient at penetrating the Blood Brain Barrier (BBB), which safeguards the brain from harmful substances.
• Increased lipid solubility generally leads to enhanced bioavailability within the central nervous system (CNS).
• Lipophilic drugs usually possess lower molecular weight and exhibit non-polar characteristics.
• Notable examples of lipid-soluble drugs include anesthetics, certain antidepressants, and antipsychotics.

Drug Permeability Mechanisms

• Diffusion: Lipid-soluble drugs primarily enter the brain through passive diffusion, thanks to their affinity for lipid bilayers.
• Transport Mechanisms:
  • Carrier-mediated transport: Certain lipid-soluble substances utilize specific transport proteins for crossing the BBB, often through facilitated diffusion.
  • Endocytosis: This process involves cell membrane engulfment, allowing larger lipid-soluble compounds to be taken up.
• Factors Affecting Permeability:
  • Molecular Size: Smaller molecules find it easier to traverse the BBB.
  • Ionization: Non-ionized (neutral) drug forms have a higher likelihood of penetrating the BBB.
  • Physicochemical Properties: Factors such as lipophilicity, solubility, and charge significantly affect a drug's BBB crossing ability.
• Pathological Conditions: Conditions like inflammation or injury can modify BBB permeability, permitting more drugs and potentially harmful elements to reach the CNS.
• Examples:
  • Lipid-soluble drugs such as diazepam, morphine, and propranolol demonstrate effective penetration into the CNS.
  • Conversely, water-soluble drugs like aminoglycosides and penicillin generally struggle to access the brain.
• Recognizing the relationship between lipid solubility and drug permeability mechanisms is vital in drug design aimed at CNS therapeutic applications.

Test your understanding of drug absorption and the critical thinking necessary for safe medication administration in nursing. This quiz focuses on clinical decision-making processes essential for providing quality patient care and clinical judgment.