Prescribing for Children: Paediatric Pharmacokinetics and Clinical Governance

Comprehensive practice flashcards reviewing paediatric pharmacokinetics, absorption routes, distribution, metabolic maturation, dosing calculations, licensing, and clinical governance.

According to paediatric prescribing terminology, what age ranges define a neonate, an infant, and a toddler?

A neonate is $0\text{--}28\text{ days}$, an infant is $1\text{--}12\text{ months}$, and a toddler is $1\text{--}2\text{ years}$.

According to paediatric prescribing terminology, what age ranges define a preschooler, a school-age child, and an adolescent?

A preschooler is $2\text{--}5\text{ years}$, a school-age child is $6\text{--}11\text{ years}$, and an adolescent is $12\text{--}18\text{ years}$.

Which four gastrointestinal factors affecting oral drug absorption are reduced in neonates?

Gastric emptying time, gastric acid secretion, bile salt formation, and intestinal motility are all reduced in neonates.

Why should oral medications not be added directly to a child's feed or milk?

Adding drugs to feed or milk creates a risk of incomplete dosing and potential food-drug interactions.

Why should intramuscular (IM) injections generally be avoided in neonates and young children?

IM injections are painful, can cause tissue damage, and result in erratic or decreased absorption because neonatal muscle mass is small and poorly perfused.

What three physiological factors lead to greater topical drug absorption in newborns and young infants?

An immature epidermal barrier, increased skin hydration, and a higher surface area to body weight ratio.

At what age should topical EMLA cream be avoided due to the risk of systemic toxicity?

Topical EMLA cream should be avoided in children under $1\text{ year}$ of age.

What are the main advantages and disadvantages of rectal drug administration in children?

Advantages: Avoids first-pass metabolism, stomach acid, and gastric irritancy. Disadvantages: Absorption is variable depending on retention, young infants may expel the drug prematurely, and the route can be distressing.

Why are dry powder inhalers generally unsuitable for children below school age?

Most children below school age lack the administration technique and inspiratory effort required to operate dry powder inhalers correctly.

How do total body water and body fat percentages change between a pre-term infant and a 1-year-old child?

Total body water decreases from $85\%$ in pre-term infants to $60\%$ at $1\text{ year}$, while body fat increases from $3\%$ in pre-term infants to a peak of $30\%$ at $1\text{ year}$.

Why do neonates require lower serum levels of phenytoin compared to older patients?

Neonates have lower levels of serum albumin, resulting in less protein binding and a higher proportion of free, active drug.

By what mechanism can sulphonamides induce kernicterus in neonates?

Sulphonamides displace bilirubin from binding sites on albumin, causing a rise in unbound plasma bilirubin that can cross the blood-brain barrier.

How does Phase I drug metabolism change between infancy, young childhood, and puberty?

Phase I metabolism is reduced in neonates and rises over the first $6\text{ months}$; it can exceed adult rates in young children (requiring higher doses per kg) and gradually declines during adolescence to adult levels at puberty.

At what age does the Phase II metabolic pathway of glucuronidation typically reach adult levels?

Glucuronidation does not reach adult levels until around $3\text{ years}$ of age.

How does paracetamol metabolism differ between paediatric patients and adults?

Paracetamol is metabolised primarily via the sulphate conjugation pathway in children and via the glucuronidation pathway in adults.

How does the elimination half-life of caffeine compare between a neonate and an adult?

The half-life of caffeine is $95\text{ hours}$ in a neonate compared to $4\text{ hours}$ in an adult.

At what ages do glomerular filtration rate (GFR) and renal blood flow reach adult levels in paediatric development?

GFR reaches adult levels by $3\text{--}5\text{ months}$, whereas renal blood flow reaches adult levels by $1\text{ year}$ of age.

At what age is complete maturation of renal function achieved, and how does this affect digoxin half-life?

Complete renal maturation occurs at $6\text{--}8\text{ months}$. Digoxin half-life is $20\text{--}70\text{ hours}$ at under $2\text{ months}$ of age, falling to $12\text{--}42\text{ hours}$ at $2\text{--}18\text{ months}$.

Why are inhaled $\beta_2$ agonists relatively ineffective in infants under $6\text{ months}$ of age?

In infants under $6\text{ months}$, $\beta_2$ receptors are relatively unresponsive to $\beta$ agonists.

What adverse pharmacodynamic effect are children more susceptible to when administered metoclopramide?

Children are more likely to experience extrapyramidal side effects from metoclopramide.

What percentage of medicines administered on a children's ward are typically prescribed off-licence?

Approximately $25\%$ of medicines on a children's ward are prescribed off-licence.

Who holds legal and clinical responsibility when harm occurs from an unlicensed medicine versus a licensed medicine?

The pharmaceutical company is responsible for harm resulting from a licensed medicine, whereas the Independent Prescriber bears full clinical and professional responsibility for prescribing an unlicensed or off-label medicine.

What is the RCPCH and NPPG guidance regarding consent for prescribing unlicensed medicines in children?

Informed use of unlicensed medicines is necessary in paediatric practice, and it is not legally necessary to obtain consent beyond that taken when prescribing licensed drugs.

How does the harm potential of paediatric medication errors compare to adult medication errors in a hospital setting?

Paediatric medication errors occur at similar rates to adults, but they have three times the potential to cause harm.

What specific adverse drug reaction restricts the use of tetracyclines in children?

Tetracyclines deposit directly into growing teeth and bones, leading to permanent staining and potential skeletal harm.

Which physiological parameter corresponds most closely to changing drug dose requirements across childhood?

Body surface area (BSA) corresponds most closely to changing paediatric drug dose requirements.

How are paediatric doses typically specified for drugs with narrow versus wide therapeutic indices?

Narrow therapeutic index drugs (e.g., cytotoxic agents like methotrexate) are dosed per square metre ($\text{m}^2$) of body surface area, while wide therapeutic index drugs (e.g., penicillins) are quoted for wide age bands.

According to Public Health England growth reference charts, which centiles define overweight and obesity in children?

Overweight is defined as the $91\text{st}\text{ centile}$ and over, and obese is defined as the $98\text{th}\text{ centile}$ and over.

Why does weight-based dosing using total body weight pose an overdose risk in obese paediatric patients?

The excess body weight in obese children does not consist of normal proportions of lean tissue and fat, risking drug overdose if dosing is calculated from total body weight.