Paediatrics vs. Geriatrics - Key Differences

1. Definition & Age Groups

2. Physiology

Paediatrics

• Organ systems are immature and still developing
• Higher metabolic rate and body surface area-to-weight ratio
• Thinner stratum corneum - greater risk of systemic toxicity from topical drugs
• Immature blood-brain barrier - risk of kernicterus (e.g., from ceftriaxone in neonates)
• Decreased gastric emptying and higher gastric pH in neonates - prolongs drug exposure before pylorus passage
• Immune system immature - higher susceptibility to certain infections

Geriatrics

• Organ function declines at ~1% per year after age 30 (Goldman-Cecil Medicine)
• Reduced cardiac reserve, renal function, hepatic metabolism, pulmonary capacity
• Sarcopenia (muscle loss), osteopenia/osteoporosis
• Decreased thirst sensation - risk of dehydration
• Reduced baroreflex sensitivity - orthostatic hypotension

3. Pharmacokinetics (Drug Handling)

Paediatrics

• Absorption: Slower gastric emptying, higher pH in neonates alters oral drug absorption
• Distribution: Higher total body water, lower plasma protein (altered drug distribution); weight-based dosing is essential but must account for age-related renal development - not just weight (e.g., gentamicin dosing)
• Metabolism: Immature hepatic enzyme systems (CYP enzymes); e.g., codeine via CYP2D6 ultrarapid metabolism can cause fatal morphine toxicity in neonates
• Excretion: Immature renal function, especially in neonates - drugs eliminated more slowly

Geriatrics

• Reduced renal clearance - many drugs accumulate (e.g., digoxin, aminoglycosides, NSAIDs)
• Reduced hepatic first-pass metabolism - higher bioavailability of some oral drugs
• Increased body fat, decreased lean mass - lipophilic drugs have longer half-lives
• Reduced albumin in frail elderly - more free (active) drug for highly protein-bound drugs
• Polypharmacy is the norm (64% of adults ≥65 have ≥2 chronic conditions) - drug interactions are common

4. Disease Patterns

Paediatrics

• Congenital/genetic disorders (heart disease, metabolic disorders, chromosomal syndromes)
• Infectious diseases - RSV, rotavirus, meningitis, otitis media
• Developmental disorders - autism, ADHD, cerebral palsy
• Malignancies - leukaemia, brain tumours, Wilms tumour (childhood-specific)
• Asthma, febrile seizures, failure to thrive
• Acute illnesses tend to be single-system in younger children

Geriatrics

• Multimorbidity is the rule - at age ≥65, 64% have ≥2 chronic conditions vs. only 7% of those aged 18-44 (Goldman-Cecil Medicine, Table 22-1)
• Cardiovascular disease - hypertension, heart failure, atrial fibrillation, coronary artery disease
• Neurodegenerative diseases - Alzheimer's, Parkinson's, vascular dementia
• Metabolic - type 2 diabetes, hypothyroidism, osteoporosis
• Geriatric syndromes (unique to this population): falls, delirium, frailty, urinary incontinence, pressure ulcers, malnutrition, cognitive impairment - these arise from accumulated impairments across multiple domains, not a single disease

5. Drug Safety Concerns - Specific Examples

Paediatric-Specific Drug Toxicities (from Rosen's Emergency Medicine)

Geriatric-Specific Drug Risks

• NSAIDs - GI bleeding, renal failure, fluid retention
• Benzodiazepines - falls, delirium, prolonged sedation
• Anticholinergics - confusion, urinary retention, constipation
• Antihypertensives - orthostatic hypotension and falls
• Anticoagulants - bleeding risk higher due to polypharmacy interactions

6. Assessment Approaches

7. Key Philosophical Differences

• Rosen's Emergency Medicine (paediatric pharmacokinetics, drug toxicity table, p. 3322)
• Goldman-Cecil Medicine (geriatric syndromes, multimorbidity table, geriatric assessment, p. 235-237)
• Kaplan & Sadock's Comprehensive Textbook of Psychiatry (paediatric drug dosing and PK extrapolation)

Differences Between Paediatrics and Geriatrics

Paediatrics deals with growing, immature organ systems in children requiring weight-based dosing, while geriatrics deals with declining, degenerated organ systems in the elderly requiring dose reduction and polypharmacy management.

Drugs That Decrease Breast Feeding (Reduce Milk Production / Suppress Lactation)

Mechanism First (Important for Viva)

Drugs That Decrease Breast Milk

1. Dopamine Agonists (Most Important Group)

"Dopamine agonists such as bromocriptine inhibit prolactin secretion" - Costanzo Physiology, 7th Ed.

2. Estrogens

• High-dose estrogen (e.g., combined oral contraceptive pills) suppresses lactation
• Mechanism: directly inhibits milk secretion at breast tissue level
• Low-dose progestin-only pills are safe during breastfeeding

3. Pseudoephedrine / Decongestants

• Reduces milk supply by vasoconstriction and direct glandular effect
• Even a single dose can reduce output

4. Diuretics

• Furosemide in high doses - reduces fluid available for milk
• Thiazides can also reduce milk volume

5. Ergotamine

• Dopaminergic activity - used in the past to suppress lactation

6. Alcohol (chronic heavy use)

• Inhibits oxytocin release - impairs milk ejection (let-down reflex)

7. Drugs that increase Dopamine (indirectly)

• Amphetamines, cocaine - dopaminergic, reduce prolactin

Memory Table

Prolactin Inhibitory Factors (Table from Costanzo Physiology)

Dopamine agonists (bromocriptine, cabergoline) are the main drugs that decrease breastfeeding by inhibiting prolactin secretion from the anterior pituitary.

Drugs Contraindicated During Lactation

Mechanism of Transfer

• Low molecular weight
• High lipid solubility
• Low protein binding
• Unionized form (high pKa for bases)

WHO Classification - Drugs & Breastfeeding

Detailed List by Drug Class

Absolutely Contraindicated

Avoid (Use Only if No Alternative)

Use With Caution / Monitor Infant

Drugs SAFE in Lactation (for comparison)

• Paracetamol (acetaminophen)
• Penicillins, cephalosporins
• Heparin (does not cross into milk)
• Insulin
• Progestin-only contraceptives
• Loratadine (antihistamine)

Viva One-Liner

Drugs absolutely contraindicated in lactation include anticancer drugs, radioactive iodine, amphetamines, ergotamines, statins, and chloramphenicol - they either harm the infant directly or suppress milk production.