Pharmacokinetics - Absorption: Nursing Pharmacology

Overview of Pharmacokinetics

• Pharmacokinetics involves the movement and modification of medication within the body.
• Four key components of pharmacokinetics (ADME):
  • Absorption: Movement from the site of administration to the bloodstream.
  • Distribution: Dispersion throughout body tissues.
  • Metabolism: Chemical breakdown of the substance.
  • Elimination: Excretion from the body.

Absorption

• Definition: Process by which a drug moves from administration site to the bloodstream.

Mechanisms of Absorption

• Passive Transport: No energy required.
  • Passive Diffusion: Movement of small, lipid-soluble, nonpolar medications across membranes.
  • Facilitated Diffusion: Movement of larger, water-soluble, polar medications through transport proteins (channels/carrier proteins).
• Active Transport: Requires energy (ATP) to move substances against their concentration gradient.
  • Utilizes specific carrier proteins.

Factors Affecting Absorption

• pH of Environment:
  • Weak acids absorb better in acidic environments (proximal duodenum).
  • Weak bases absorb better in alkaline environments (distal ileum).
  • Stomach is not ideal for absorption due to thick mucus layer.
• Surface Area:
  • Larger surface areas, like the small intestine, enhance absorption.
• Blood Supply: Adequate blood supply to the absorption site enhances the rate & extent of absorption.
• Presence of Other Substances:
  • Certain foods can inhibit or promote drug absorption.

Routes and Preparations

• Sublingual Administration: Bypasses stomach acids, enhancing absorption rate and extent.
• Pharmaceutical Preparations:
  • Enteric coatings protect drugs from stomach acids, dissolve in the intestine.

Bioavailability

• Definition: The proportion of a drug that enters circulation when introduced into the body.
  • Example: If 100 mg of aspirin is taken orally and 60 mg is absorbed, bioavailability is 60%.

Clinical Considerations

• Review patient medical history for conditions affecting absorption (e.g., gastroparesis, decreased GI circulation).
• Apply pharmacokinetic principles when administering medication to ensure effective absorption and patient safety.