There is a separate British National Formulary (BNF) for prescribing in children (BNFc). It is an indispensible resource and amongst other useful material, at the very back of the book it contains tables for estimating body surface area using a child’s weight and a guide table for ideal weight.
Doses differ depending on the child’s age and weight and some drugs doses are calculated using body surface area (see BNFc for body surface area table).
The maximum dose which can be given is the adult dose. So if the calculation of milligrams per kilogram comes to a total of 420 mg but the adult dose is 400 mg, you would prescribe 400 mg for the child.
Use ideal body weight for overweight children. If a child is obese, the dose must be calculated based on their ideal body weight to ensure that it is appropriate for their organ function at that age. Check the guide table in the BNFc or growth charts to estimate ideal body weight.
Round up or down to a sensible amount. Bear in mind when prescribing how the dose will be measured by the person drawing up and administering the medications; it may be more sensible to round up or down from the calculated dose. For example, co-amoxiclav comes in vials of 600 mg so if your calculation comes to 595 mg then rounding up and prescribing 600 mg is much more sensible. For unit sizes, check the BNFc, ask the pharmacist or the ward sister.
Don’t forget to specify the strength if prescribing by volume. Some drugs in the BNFc are given as volumes (mL) rather than doses (mg) and parents also tend to describe their child’s medication in volume (mL or spoonfuls), but you need to find out the strength of the preparation before you prescribe as some medicines come in different strengths, e.g. furosemide solution is available in four strengths from 5 mg/5 mL up to 50 mg/5 mL. This is particularly important when the preparation has been specifically tailored for the patient.
Never prescribe whilst distracted
Allergies
Calculate dose by weight or body surface area
Minimum number of doses per day
Some drugs are quoted as mg/kg/dose and some mg/kg/day
Never exceed adult dose
Write ‘micrograms’ and ‘units’ in full (don’t abbreviate and risk drug errors)
Always check the BNFc
Double check with pharmacist or senior colleague/paediatrician if unsure
Use ideal body weight to calculate doses for obese children
Be careful and clear in your use of decimal points
Be conscious of the potential for ten-fold prescribing errors (some of your patients may weigh 5 kg whilst others weigh 50 kg
Many drugs are prescribed ‘off-licence’. Most drugs have come to market following testing on adults but their use has never been researched in children. This means that many, even very commonly used drugs are prescribed ‘off-licence’ when they are prescribed for children. This does not make much difference in practical terms and the BNFc will list those which are not formally licensed for use in children (and then list a whole load of doses for that drug in different age groups!). It is useful to be aware of this so that you can consider trying to use a drug which is licensed for children in situations where there are several possible alternatives to choose from. The Medicines for Children Research Network has been created in order to co-ordinate and increase the volume of much-needed research into medicines for children. Its webpage (www.mcrn.org.uk) has some useful pages for parents and children about what research trials involve and how they can help improve care for children by taking part.
Top TipGetting children to actually take what you prescribe
A particularly important consideration in paediatric prescribing is compliance. It’s all very well writing a medication on the drug chart but if the child spits it all out, the drug won’t be doing much other than making a mess!
Some suggestions to aid compliance with medication include the following.
Try to keep regimes to a maximum of twice daily where possible.
Use the formulation that is the best tolerated – ask your ward pharmacist and nursing staff which formulations are best tolerated and if a particular drug can be disguised in something more tasty. In some instances, drugs are so poorly tolerated due to their taste that they are avoided completely in some paediatric departments (e.g. flucloxacillin).
Explain what the medication is for. In older children, explaining to them in simple terms what their medications are for can aid compliance. Always involve parents in decisions about medications in younger children. Teenagers may prefer not to have their parents involved and it is important to respect their requests where possible. See Chapter 3 on assessment of Gillick Competence and consent in teenagers.
Help children and families to understand more about their medications. The Medicines for Children website (www.medicinesforchildren.org.uk) is a fantastic resource. It contains lots of information about specific medications and more general principles of giving medication to children. You can print information leaflets about specific drugs for parents or refer them directly to the website itself.
Think about discharge plans. Consider how medications are going to be taken once the child has gone home. For outpatient or discharge medication, consider the timing of doses (avoid school-time doses if at all possible) and also prescribe doses rounded to easily measurable quantities (e.g. 5 mL spoonfuls) where possible.
Fluids
For initial intravenous (IV) fluid resuscitation of children in shock or with diabetic ketoacidosis, please also see Chapter 5 – Common Paediatric Emergencies.
Children who need to be kept nil by mouth or who are severely dehydrated will need IV fluids. When prescribing maintenance fluids (e.g. whilst a child is awaiting surgery), you need to meet their baseline requirements of fluids, electrolytes and glucose. For children who are dehydrated, assess the clinical severity of dehydration and from this, how much fluid they will need to be given in addition to their baseline requirements. Parenteral (i.e. oral or nasogastric) fluid is a much safer option where possible so only prescribe fluid intravenously when absolutely necessary.
Maintenance fluids
Please note that the fluid regimes below do not apply to babies who are less than 1 year old. For maintenance fluid regimes in babies under 1 year see Chapter 9 – Neonates.
For maintenance fluids in children, many hospitals use 0.9% sodium chloride and 5% dextrose, i.e. the bag contains equal parts 0.9% saline and 5% dextrose. 5% dextrose with ‘half normal saline’ (i.e. 0.45% saline and 5% dextrose) is rarely used now as it can cause hyponatraemia. Fluids are normally only available in 500 mL bags on the children’s ward. Add 10 mmol of potassium to each 500 mL of fluid to meet the daily requirements for children who have normal potassium levels. This is a commonly used regime but check your local hospital guidelines for the preferred fluid maintenance regime.
Top TipSee Box 7.2 for worked examples of calculations for maintenance fluid.
Replacement therapy
Oral replacement of fluids is the safest option where possible for a child with mild-to-moderate dehydration. If a child is not tolerating fluids orally you should also consider giving fluid via nasogastric (NG) tube before thinking of IV fluid replacement.
For trials of oral replacement, use oral rehydration salts solution (a common brand is Dioralyte). Aim to correct the child’s fluid deficit over a period of 4 h; this can either be given as a small volume every 10 min or as a continuous NG infusion (see example 1 in Box 7.4 for calculations).
For children who require IV fluids, you need to consider how dehydrated they are and how quickly to replace their fluid deficit.
Traditionally, a child’s additional fluid requirements are calculated by assessing their percentage dehydration. This is what people mean when they mention that a child needs ‘MAINTENANCE PLUS 5%.’ If you are saying you think that a child is 5% dehydrated, this means that you think they have lost 5% of their body weight as a result of fluid loss. Every 1 g of body weight lost is the equivalent of 1 mL of fluid loss. This means that if you have a recent weight for the child when they were well and today’s weight, you can calculate how much weight (and therefore how much fluid) they have lost. You then know exactly how much fluid they will need in addition to the normal maintenance requirements (as mentioned above). This is much more commonly used for babies, who are weighed frequently, but can be used for children if, for example, they have recently been weighed at an outpatient appointment.
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