Pharmacokinetics - Elimination: Nursing Pharmacology

Introduction to Pharmacokinetics

• Pharmacokinetics: Movement and modification of a medication in the body.
• ADME: Acronym for Absorption, Distribution, Metabolism, and Elimination.

Focus on Elimination

• Elimination: Removal of medications and their metabolites via excretion.
• Primary organ: Kidneys.
  • Glomerular filtration: Medications filtered out as blood flows through the glomerulus.
  • Renal tubules:
    • Active secretion: Medications from peritubular capillaries into the tubular lumen.
    • Passive reabsorption: Some medications reabsorbed into the bloodstream.
• Excretion: Medications not reabsorbed are excreted via urine.

Alternative Routes of Elimination

• Gastrointestinal (GI) tract:
  • Oral medications: Not absorbed, passed in feces.
  • Enterohepatic circulation: Medication transferred by liver to bile.
    • Bile release: Medication reabsorbed into portal circulation, returning to liver.
    • Cycle repeats: Eventually eliminated via feces.
• Other excretion methods: Lungs (exhaled air), sweat, saliva, tears, breast milk.

Factors Affecting Elimination

• Impaired renal function: Decreased cardiac output reduces glomerular filtration, leading to medication buildup.
• Urine pH:
  • Alkaline urine: Acidic medications not reabsorbed, excreted in urine.
• Impaired hepatic function: Slows metabolism, prolongs medication presence in the body.
• Drug interactions:
  • Example: Probenecid slows penicillin elimination, increasing effectiveness.

Medication Half-Life

• Definition: Time for blood concentration of medication to reduce by half.
• Influence: Depends on metabolism and elimination phases.
  • Example: 2-hour half-life means concentration drops from 100 to 50 mg/liter in 2 hours.

Key Takeaways for Nursing

• Consider pharmacokinetic principles before medication administration, focusing on elimination processes.

References

• "Focus on Nursing Pharmacology" LWW (2019)
• "Pharmacology" Elsevier Health Sciences (2014)
• "Mosby's 2021 Nursing Drug Reference" Mosby (2020)
• "Saunders Comprehensive Review for the NCLEX-RN Examination" Saunders (2016)
• "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education/Medical (2017)
• "Lehne's Pharmacology for Nursing Care" Saunders (2018)
• "Medication Safety Tips for the Breastfeeding Mom" Healthy Children (2015)