Paediatric Prescribing

Question 1

Why should aspirin be avoided in children?

Answer 1

Associated with Reyes Syndrome (excessive vomiting, tachypnoea, seizures, anxiety, hallucinations, irritability)

Question 2

How is GI motility (and therefore oral absorption) different in neonates and infants?

Answer 2

Gastric emptying is slower so there is increased oral absorption

Question 3

How is the luminal pH different in children under 3 years and how does this affect oral drug absorption?

Answer 3

After birth the gut pH is >4 which increases the absorption of acid-labile drugs.

Question 4

Why do topical drugs have a greater systemic effect in children?

Answer 4

Skin in thinner so more percutaneous absorption can occur

Larger surface area of skin relative to body weight

Question 5

Why are IM drugs more rapidly absorbed in children?

Answer 5

Increased capillary density in muscles so increased take up of drug into bloodstream

Question 6

Why are inhaled drugs more rapidly absorbed in children?

Answer 6

The lungs are immature so drugs can enter the bloodstream more easily

Question 7

How does % body water (and therefore volume of distribution) change from a premature neonate to an adult?

Answer 7

Premature neonate - 80% water
Full term - 70% water
10 years old- 65% water
Adult- 54% water

In infants the volume of distribution is higher and so water soluble drugs will be at a lower concentration in the body.

Question 8

Give 3 reasons why paediatric prescribing errors may occur

Answer 8

Doses are calculated individually off weight
Drugs are commonly prescribed off label
Shortage of paediatric clinical trials
Drugs not available in child friendly forms

Question 9

Give a risk of prescribing ibuprofen in children who are dehydrated

Answer 9

Renal damage

Question 10

How does fewer plasma proteins in the blood affect drug distribution in infants?

Answer 10

Fewer plasma proteins means more free/unbound drug in the plasma to exert therapeutic effects

Question 11

Give 5 factors that affect drug distribution in the body

Answer 11

% body water 
Plasma proteins
Regional blood flow 
Organ perfusion 
Cell membrane properties 
Cardiac output 
Acid-base balance

Question 12

Before the age of 3 how does the gastric pH affect drug absorption?

Answer 12

<3 years old- pH >4 which increases absorption of acid-labile drugs.

After 3 years, pH drops to 1-2

Question 13

Why can caffeine only be used as a respiratory stimulant before 3 months of life?

Answer 13

At 3 months old, the liver enzyme CYP1A2 develops which demethylates caffeine and starts phase 1 metabolism.

Question 14

What is the GFR of a term neonate?

Answer 14

2-4 ml/min/1.73squared

Question 15

How does a low neonatal GFR affect drug excretion?

Answer 15

Low GFR means renally excreted drugs will remain in the body for much longer

Question 16

How can weight be estimated in a child for emergency drug prescribing?

Answer 16

(Age + 4) x 2

Or:
0-12 months: (0.5 x age in months) + 4
1-5 years: (2 x age in years) + 8
6-12 years: (3 x age in years) + 7

Question 17

How is weight estimated from length in infants?

Answer 17

Use Breslow tape

Question 18

How is Body Surface Area calculated in infants?

Answer 18

Uses weight only- conversion chart in BNFC

Question 19

Why is body surface area used over weight in dosing toxic drugs like chemotherapy?

Answer 19

Thought to correlate more closely with variation in age, body size and body composition

Question 20

Which fluids are given as routine maintenance fluids in children?

Answer 20

0.9% Sodium Chloride

Isotonic crystalloid

Question 21

How is the maintenance fluid dose over 24 hours calculated in children?

Answer 21

100 ml/kg for 1st 10 kg
50 ml/kg for next 10 kg
20 ml/kg for every remaining kg

Add together and divide by 24 to get the hourly rate.

Question 22

How are maintenance fluids decided in neonates?

Answer 22

Depends on gestation, day of life, weight, BM and electrolytes.

Usually given 0.9% NaCl with 5-10% of glucose

Question 23

Give 4 red flag indicators that a child needs IV rehydration

Answer 23

Appears unwell 
Lethargic 
Sunken eyes 
Tachycardia
Tachypnoea 
Reduced skin turgor

Question 24

If rehydrating orally, how much should be given over 4 hours?

Answer 24

50 ml per kg in small frequent drinks or via NG tube

Question 25

If rehydrating parentally (IV), how much of what fluid should be given over 24 hours?

Answer 25

50 ml/kg of 0.9% sodium chloride + 5% glucose over 24 hours

+ maintenance fluids

Question 26

If a patient is in shock, what bolus of fluid is given before rehydration and maintenance fluids are started?

Answer 26

20 ml/kg bolus of 0.9% saline

Increase rehydration fluids to 100 ml/kg

Question 27

What is an off label drug?

Answer 27

Drug used for conditions outside marketing authorisation

Question 28

What is an unlicensed drug?

Answer 28

Drug with no marketing authorisation

Question 29

What criteria must be met to prescribe an off label or unlicensed drug?

Answer 29

No suitable licenced alternative
Sufficient evidence for its use
You take responsibility for prescription and patient care
Decision and rational documented in notes
Inform patient and parent and get consent.

Question 30

Give 4 ways to avoid paediatric prescribing errors

Answer 30

Check doses against BNFC
Check allergies 
Check weight, age, BSA
Avoid decimal points 
Get 2nd person to check 
Write clearly 
Write out units in full 
Round doses to a sensible value

Question 31

How can adherence be improved in children?

Answer 31

Shorter courses
Time doses to avoid school
Avoid unacceptable side effects
Age appropriate information
Nicer taste/ better administration methods
Educate parents on importance of adherence