Kids are not small adults

Medical Matters: "The adult may be safely treated as a child; the converse can lead to disaster." - Sir Lancelot Barrington-WardI have never been a fan of cough bottles. So I am glad to see that the US Food and Drug Administration (FDA) has advised the public not to use over-the-counter cough and cold products in children under the age of two, writes Muiris Houston.

The FDA also hinted that it may restrict the use of these remedies in all children up to the age of 11.

If I had a euro for every parent who consulted because of an older child's non-response to a cough bottle, I could be writing this column from a villa in the Caribbean. Companies market two types of cough medicine: expectorants, which are supposed to thin out phlegm and make it easier to cough up; and antitussives, designed to suppress the desire to cough.

In my experience, the availability of a wide range of over-the- counter products has merely worsened the exasperation of already sleep-deprived parents and led to an increased anxiety triggered by their child's poor response to a cough medicine.

While few cough and cold medicines are approved for use in under twos here, parents must be careful not to give products bought for older children to toddlers. According to the FDA, overdose with these drugs can cause potentially life-threatening side effects, including convulsions, dangerously fast heart rates and a reduced level of consciousness in small children.

Concerns about cough and cold remedies are just the tip of an even more alarming iceberg; almost two thirds of the thousands of medicines given to children have never been tested on them. Many drugs used in children have only ever been licensed for adult use, with paediatricians and other doctors exercising their right to prescribe drugs "off-label" in order to use a particular medication in a child under 12.

Why is this? There are obvious ethical issues when it come to testing drugs in children. Informed consent must be obtained by proxy. And how appropriate is it to offer financial incentives to parents to enrol their kids in research programmes that will not immediately benefit their child?

Economically, children consume quite a small proportion of prescription medicines so there is less financial incentive for pharmaceutical companies to carry out studies in a paediatric population. The disincentive is even greater for drugs primarily used in adults. If the companies feel that doctors are likely to use such a drug extensively in children on an "off-label" basis, then there is little economic incentive for them to evaluate the drugs in children.

Writing recently in the Irish Pharmacy Journal, editor Kate O' Flaherty said: "One of the most important points to remember when prescribing, dispensing or administering medicines to children may be stating the obvious, but children are not small adults, and can react quite differently to many drugs."

This is a key point. And from a prescribing perspective, there are five distinct categories of children: the premature baby; the newborn baby up to 28 days old; infants up to 24 months; children aged two to 11 years; and adolescents from 12 to 18 years.

Is "scaling down" adult doses when treating children acceptable? Certainly not, in the case of drugs with a narrow therapeutic index, where inaccurate dosing can make a medication both ineffective and dangerous.

How a drug is distributed, metabolised and excreted in the body differ considerably in different age groups. The distribution of a water-soluble drug will depend on the percentage of total body weight made up of water - it varies from 85 per cent in a premature baby to 55 per cent in an adult. The liver handles some drugs more rapidly in older children than adults. And the capacity of the kidneys to excrete drugs is greatly reduced in newborns.

So what is being done about the knowledge deficit in children's prescribing? In 2005, the first edition of the British National Formulary (BNF) for Children was published. Long a prescribing bible for adults, the availability of a BNF for younger people has undoubtedly helped both doctors and pharmacists.

A year ago this month, the EU brought in new legislation based on a previous consultation paper, "Better medicines for children - Proposed regulatory actions in paediatric medical products". In line with the legislation, the Irish Medicines Board has recently requested drug companies here to submit details of paediatric studies they have carried out on all drugs for which they hold a product licence.

In the meantime, it is estimated that more than 50 per cent of medicines used to treat children in Europe have not been appropriately tested. Every time a doctor writes a prescription for a child for an untested, unauthorised product, the doctor cannot be sure the medicine will be effective, he will be somewhat uncertain as to the appropriate dose, and cannot accurately predict what side effects the child may suffer.

And if this is the case with prescription-only medicines, clearly there is a need for caution with products that can be purchased over the counter. The best advice is not to give medication to children without first discussing it with your doctor or pharmacist.

Dr Muiris Houston is pleased to hear from readers at mhouston@irish-times.ie but regrets he is unable to reply to individual medical queries