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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