Pediatric and Geriatric Pharmacology

Pediatric and Geriatric Pharmacology

Pediatric and Geriatric Pharmacology

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Pediatric Pharmacokinetics & Dynamics - Tiny Patients, Big Challenges

  • Absorption (A):
    • Neonates: ↑ Gastric pH, delayed emptying.
    • Skin: ↑ Percutaneous absorption (thin, ↑ Surface Area to Body Weight ratio).
    • IM: Erratic (↓ muscle mass & flow).
  • Distribution (D):
    • Body Composition: Neonates ↑ Total Body Water (TBW, ~75-80%), ↓ Fat.
    • Vd: ↑ for water-soluble drugs, ↓ for lipid-soluble drugs.
    • Protein Binding: ↓ plasma protein binding → ↑ free drug fraction.
  • Metabolism (M):
    • Liver: Immature enzymes (Phase I CYP450 & Phase II glucuronidation ↓).
    • Risk: Chloramphenicol toxicity (Gray Baby Syndrome) due to ↓ glucuronidation.
  • Excretion (E):
    • Kidneys: ↓ Glomerular Filtration Rate (GFR) & tubular function in neonates.
    • Maturation: Renal function matures by 6-12 months; prolonged drug $t_{1/2}$ until then.
  • Pharmacodynamics (PD):
    • Receptors: Altered number, affinity, or post-receptor responses.
    • Reactions: Paradoxical drug effects possible (e.g., benzodiazepines → agitation).

⭐ Neonates have ↑ Total Body Water & ↓ body fat, significantly altering drug Volume of Distribution (Vd).

Pediatric Dosing & ADRs - Measure Twice, Dose Once

  • Dosing Methods:
    • Weight-based (mg/kg): Most common & reliable.
    • Body Surface Area (BSA): $Dose = \frac{BSA (m^2)}{1.73 m^2} \times AdultDose$. For chemotherapy, nephrotoxic drugs.
    • Age-based (Young’s, Clark’s rules): Less accurate, historical.
  • Flowchart: Choosing Dosing Method
  • Key Age-Specific ADRs: 📌 Remember CAST for major risks:
    • Chloramphenicol: Grey baby syndrome (neonates).
    • Aspirin: Reye's syndrome (children with viral illness).
    • Sulfonamides: Kernicterus (neonates, esp. premature).
    • Tetracyclines: Teeth staining & ↓bone growth (< 8 yrs).

⭐ Aspirin is contraindicated in children with viral fever due to risk of Reye's syndrome.

Geriatric Pharmacokinetics & Dynamics - Golden Years, Altered Drugs

  • Pharmacokinetics (ADME Changes):
    • Absorption: Variable; ↓ gastric acid & motility.
    • Distribution: ↓ Total body water, ↑ body fat (affects Vd); ↓ albumin (↑ free drug).
    • Metabolism: ↓ Hepatic blood flow & Phase I (CYP450) activity; Phase II often preserved.
    • Excretion: Crucial! ↓ Renal clearance (GFR). Use Cockcroft-Gault: $CrCl = \frac{(140-age) \times IBW (kg)}{72 \times SCr (mg/dL)} (\times 0.85 \text{ if female})$.
  • Pharmacodynamics:
    • Altered receptor sensitivity (e.g., ↑ to sedatives, ↓ to β-agonists/antagonists).
    • Impaired homeostatic mechanisms (e.g., postural hypotension). Aging and antibiotic use considerations

⭐ Renal function (eGFR or CrCl) is the most significant factor affecting drug dosing in the elderly.

Geriatric Prescribing & Polypharmacy - Pill Puzzles, Safe Solutions

Polypharmacy (use of ≥5 drugs) ↑risks: ADRs, drug interactions, non-adherence, falls, cognitive decline. Prescribing mantra: 'Start low, go slow,' individualize therapy, and conduct regular medication reviews.

  • Risk Mitigation Tools:

    • Beers Criteria: Identifies Potentially Inappropriate Medications (PIMs) to ↓ADRs. Key classes:
      • Strong Anticholinergics (e.g., diphenhydramine)
      • Benzodiazepines & Z-drugs
      • Chronic systemic NSAIDs
      • Certain Antipsychotics (e.g., haloperidol)
      • Sliding-scale Insulin (without basal)
    • STOPP/START Criteria: Tools to identify PIMs & prescribing omissions.
  • Common Drug-Related Problems & Culprits:

    • Falls: Benzodiazepines, antipsychotics, antihypertensives.
    • Cognitive Impairment: Anticholinergics (📌 "Can't see, can't pee, can't spit, can't shit"), sedatives.
    • Bleeding: Anticoagulants, NSAIDs, antiplatelets.

⭐ Anticholinergic drugs are a major cause of cognitive impairment and delirium in the elderly.

Medication use parameters in older adults

High‑Yield Points - ⚡ Biggest Takeaways

  • Pediatrics: ↑ Total body water affects Vd of hydrophilic drugs; immature liver/kidney function slows drug elimination.
  • Key pediatric ADRs: Gray baby syndrome (chloramphenicol), Reye's syndrome (aspirin), kernicterus (sulfonamides).
  • Geriatrics: ↓ Renal clearance is the most significant PK alteration; ↑ body fat affects Vd of lipophilic drugs.
  • Polypharmacy and ↑ sensitivity to CNS drugs (e.g., benzodiazepines) are prevalent in elderly.
  • Beers criteria helps avoid potentially inappropriate medications in older adults.

Practice Questions: Pediatric and Geriatric Pharmacology

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