Prescribing for Children

Dr U Mahamithawa Senior lecturer Paediatrics

“I used to think I was the only one kids hated... I don't know what I'd do if it weren't for you guys.”

What is Paediatrics? What are the challenges of prescribing for

children? Do children have the same pharmacokinetic

and pharmacodynamic responses to drugs as adults?

Are there special features in relation to paediatric prescriptions?

Are drugs given to lactating women secreted into their milk?

Is poisoning from accidental ingestion of drugs common among children?

Objectives

Paediatrics is concerned with the health of infants, children and

adolescents their growth and development their opportunity to achieve full potential as

adultsIn Sri Lanka children <12yrs of age come under the care

of paediatricians

Paediatrics

Paediatrics includes a range of ages – preterm and term neonate, infant, child and adolescent

Dramatic differences in pharmacokinetics, pharmacodynamics and psychosocial changes in the different age groups

Variation in bioavailability depending on age, route of administration and illness

Children detest medicines that have an unpleasant taste or cause discomfort

Dosage errors are common due to need for calculation based on size of child, dilutions for iv drugs

Challenges of prescribing for children

Pharmacogenetics genetically determined variations in drug

response Pharmacokinetics a drug’s disposition within the body absorption, distribution, metabolism and

elimination Pharmacodynamics relationship between drug

dose/concentration and response – effectiveness or toxicity

Definitions

Factors affecting oral absorption of medications

Pharmacokinetics

Parameter

Neonate Infant Child

Gastric acid secretion

Reduced Normal Normal

Gastric emptying time

Decreased Increased Increased

Intestinal motility

Reduced Normal Normal

Billiary function

Reduced Normal Normal

Microbial flora

Acquiring Adult pattern

Adult pattern

Increased total body water as a % of total body weight

total body water and ECF volume decreases with age

Neonates require higher doses of water soluble drugs on a mg/kg basis

Plasma protein binding reduced in neonates low levels of albumin and globulin altered binding capacity high bilirubin levels can displace drugs from

albumin

Distribution

Enzyme systems mature at different times may be absent or present in reduced

amounts at birth Altered metabolic pathways for some drugs Metabolic rate increased in children may need more frequent dosing or

increased doses (mg/kg)

Metabolism

Complete maturation of renal function not reached until 6-12 months of age

Before 34 wks of gestation GFR is markedly reduced

Excretion

Dosage form spitting of foul-tasting medicine inaccurate measurement of small volumes

of liquid medicines Drug interactions with food – especially milk Drug being mixed with large quantity of

food or milk – full dose might not be taken Drugs should not be mixed or administered

in a baby’s feeding bottle

Other factors affecting bioavailability

Compliance in children influenced by formulation, taste, appearance and ease of administration

Whenever possible painful IM injections should be avoided

Children should be involved in decisions about taking medicine and encouraged to take responsibility for using them correctly

Dosage form

Rate of absorption faster with a liquid compared with solid formulations

Liquid>suspension>capsule≥tablet>sustained release tablet

Children >5yrs ( and some older children!) find a liquid formulation more acceptable than tablets and capsules

For long term treatment it is possible to train a child to take tablets

An oral syringe should be used for accurate measurement and controlled administration of

liquid medicine especially if the dose is <5ml

Dosage form contd…

Liquid preparations containing sugar encourage dental caries

Sugar free medicines are preferred for long term use

Try to use products which avoid the need for administration during school hours eg. modified release prep or drugs with long half lives

Intravenous route is assumed to be the most dependable and accurate route for drug delivery but there are potential sources of error

Dosage form contd..

Children are not mini-adults paediatric doses should be obtained from a

paediatric dosage reference text NOT extrapolated from adult doses

Dosages

Most drugs calculated for body weight In over weight children body weight

calculation could result in over dosing Dose should be calculated for an ideal

weight based on height and age Body surface area calculation more

accurate than body weight

Dose calculation

Full name and address

Age and date of birth

Legal requirement in the case of prescription only medicines to state age for children <12yrs

Whenever possible state the current weight to enable dose prescribed to be checked

Unnecessary use of decimal points should be avoided eg 3mg not 3.0mg 500mg not 0.5mg

If decimals are unavoidable a zero should be written in front of the decimal point 0.5ml not .5ml

Prescription writing

Communicate, communicate, communicate with patient and family

Prescription writing

Important to report adverse reactions because..

Action of the drug and its pharmacokinetics may be different in children

Drugs are not extensively tested in children Many drugs are not specifically licenced for

use in children and are used off-label

Adverse drug reactions

Almost all drugs given to lactating women are secreted to some extent into their milk

Drug use should be as minimal as possible during (pregnancy) and lactation

Very few drugs are contraindicated during lactation

Drugs in human milk

>50% of human poisoning exposures occur in children <5ys

Almost all these exposures are unintentional

>90% of these occur in the home

Ingestion is the most common route of poisoning

Safety in the home