Prescribing in special populations

Question 1

Problem meds in children (6 examples)

Answer 1

Antihistamines: paradoxical excitation

Aspirin: Reyes Syndrome-rash, vomiting, liver damage

Chloramphenicol (antibiotic): grey baby syndrome

Phenothiazine anti-emetics: prochlorperazine-extrapyramidal side effects

Sulphonamides: risk of kernicterus if under 2 mnths

Tetracyclines: teeth discolouration, impaired bone growth if under 8

Question 2

PK changes: Absorption-children

Answer 2

Acidic pH only develops in stomach by 2 years

Gastric emptying delayed in infants under 6-8 mnths, shorter in older infants

intestinal mucosa immature

Frequent feeding

IM: variable blood flow to muscles in neonates

Percutaneous absorption faster and more extensive

Rectal absorption does not change with age

Question 3

PK changes: Distribution-children

Answer 3

Increased body water: fat ratio (highest in neonates)

Plasma protein binding lower (neonates)

Membrane permeability: BBB immature, larger CNS volume

Question 4

PK changes: Metabolism-children

Answer 4

Reduced hepatic metabolism in neonates, reaching adult levels by 6-12 months, then exceed adult levels for 1-4 years, returning to adult levels by adolescence

Liver volume, blood flow and biliary function correlate well with Body Surface Area (BSA)

Question 5

PK changes: Excretion-children

Answer 5

Clearance increases non-linearly with weight so the maintenance dose per kg is highest around 2 years of age

Renal function reaches maturity ~ age 1-2 years, when the GFR correlates well with the BSA