Pediatrics Study Guide

📖 Core Concepts Pediatrics: Medical specialty caring for infants, children, adolescents, and young adults (up to 18 y in Commonwealth, 12 y in India, 21 y per AAP, sometimes 26 y for subspecialists). Pediatrician: Physician who practices pediatrics (also “paediatrician”). Physiologic principle: Children are not “small adults” – their immature organs change drug absorption, distribution, metabolism, and elimination. Absorption: Neonates have higher gastric pH and slower gastric emptying → greater oral absorption of acid‑labile drugs. Distribution: Higher total body water & extracellular fluid → larger volume of distribution (Vd) for hydrophilic drugs; fewer plasma proteins → less protein binding, more free drug. Metabolism: Hepatic Phase I & Phase II enzymes mature at different ages, altering clearance and half‑life across neonates → infants → older children. Elimination: Renal clearance relatively high in term infants (larger kidneys per kg) but markedly reduced in pre‑term neonates; disease can further impair clearance. Ethical/Legal: Consent – parents/guardians give legal permission; adolescents may have limited rights depending on jurisdiction. Assent – child’s affirmative agreement, supplementing parental consent. Best‑interest standard – ethical principle (UN CRC 1989; AAP 1995) guiding decisions for children. --- 📌 Must Remember Age limits: Commonwealth ≤ 18 y; India ≤ 12 y; AAP ≤ 21 y (some subspecialists ≤ 26 y). Neonatal gastric pH ≈ 6–7 (vs ≈ 1–3 in adults) → ↑ absorption of drugs degraded by acid. Total body water ≈ 75 % of body weight in neonates vs ≈ 60 % in adults. Plasma protein (albumin) concentration is lower in infants → ↑ free fraction of highly protein‑bound drugs. Phase I enzymes (e.g., CYP450) mature first; Phase II (e.g., glucuronidation) mature later → dosing adjustments needed especially in the first year. Pre‑term neonates: renal clearance markedly reduced → avoid adult dosing regimens. Assent is required when the child is capable of understanding (≈ 12–13 y onward). Best‑interest standard overrides parental wishes when a child's health is at risk. --- 🔄 Key Processes Oral drug absorption in infants Higher gastric pH → less acid degradation. Slower gastric emptying → prolonged absorption window. Age‑dependent intestinal enzyme activity → variable first‑pass metabolism. Hepatic metabolism maturation Phase I (oxidation, reduction, hydrolysis): activity rises rapidly in first months. Phase II (conjugation): slower, often reaches adult levels by 2–3 y. Result: drug half‑life shortens as child ages. Renal elimination development GFR rises from 30 % of adult value at birth to adult levels by 1 y. Pre‑term neonates: GFR < 30 % → dose reductions or extended dosing intervals required. Ethical decision workflow Obtain parental consent. Assess child’s capacity → seek assent if age/understanding permits. Apply best‑interest standard to resolve conflicts. --- 🔍 Key Comparisons Children vs. Adults Gastric pH: high (basic) vs. low (acidic). Gastric emptying: slower vs. faster. Plasma protein binding: low vs. high. Volume of distribution for hydrophilic drugs: larger vs. smaller. Term neonate vs. Pre‑term neonate Renal clearance: relatively high vs. markedly reduced. Kidney maturity: functional nephrons vs. under‑developed nephrons. Assent vs. Consent Assent: child’s affirmative agreement, based on capacity. Consent: legal permission from parent/guardian (or emancipated minor). --- ⚠️ Common Misunderstandings “Children are just small adults.” → Leads to adult dosing, ignoring higher water content and different protein binding. All adolescents can consent. → Legal age varies; many jurisdictions still require parental consent. Renal clearance is always high in infants. – True for term infants, false for pre‑term or those with renal disease. Assent replaces parental consent. – Assent supplements but does not replace consent. --- 🧠 Mental Models / Intuition “Water‑rich, protein‑poor” model: Imagine a newborn as a sponge (lots of water) with few “hooks” (protein). Hydrophilic drugs spread widely; highly protein‑bound drugs stay more free. “Maturation ladder” for metabolism: Phase I enzymes climb the ladder quickly; Phase II climbs later. Drug clearance improves as the child ascends. “Two‑voice decision” – Think of treatment decisions as a duet: one voice (parent) sings the legal part, the other (child) adds the assent melody; the harmony must follow the best‑interest score. --- 🚩 Exceptions & Edge Cases Pre‑term neonates: severely reduced GFR and tubular secretion → avoid drugs cleared renally or use extended intervals. Renal disease in any child: treat as adult with impaired renal function → dose reduction regardless of age. Adolescents with mature decision‑making capacity (≈ 13 y+): may consent to reproductive health, mental health, or substance‑use treatment in many jurisdictions. Subspecialty care (e.g., neonatology) may extend pediatric age limit up to 26 y for continuity of care. --- 📍 When to Use Which Hydrophilic antibiotics (β‑lactams) → dose based on total body water (mg/kg) rather than adult dosing. Highly protein‑bound drugs (e.g., warfarin) → consider free‑drug monitoring in infants because of low albumin. Acid‑labile oral meds (e.g., penicillin G) → expect increased absorption in neonates; may need lower dose or monitor levels. Renally cleared drugs → use age‑adjusted GFR (or Schwartz formula) to decide dosing interval; switch to weight‑based dosing for pre‑term infants. Ethical decisions → apply parental consent + child assent when child ≥ 12 y and capable; default to best‑interest if conflict arises. --- 👀 Patterns to Recognize High gastric pH + acid‑labile drug → anticipate greater systemic exposure. Low plasma protein + high protein binding → look for elevated free drug levels and potential toxicity. Rapid increase in Vd with age → dosing of hydrophilic agents shifts from mg/kg to mg/m² as child grows. Improving renal function curve → dosing intervals can be shortened after the first year of life. Assent present + parental dissent → check best‑interest standard for resolution. --- 🗂️ Exam Traps “Give adult dose to a 5‑year‑old” – distractor; ignore water‑distribution and protein‑binding differences. “All neonates have high renal clearance” – wrong for pre‑term infants; look for gestational age clues. “Adolescent consent is always sufficient” – many exams test jurisdictional limits; parental consent may still be required. “Assent replaces consent” – trap; assent is supplementary, not substitutive. “Best‑interest standard means parents decide everything” – misinterpretation; best‑interest can overrule parental wishes when child’s health is at risk.