• Are common but under-recognised in children.
  
• All suspected and proven adverse drug reactions (ADR) should be reported, even if seemingly trivial.
  
• Suspected allergic reactions should be assessed and followed up (e.g. by a drug allergy clinic).
  
• When an avoidable ADR is identified, patients should be given a permanent record (e.g. card or medical alert bracelet) as appropriate.

The important points to document on history are:

• The specific illness the medication was prescribed for (intercurrent viral infections may also cause urticaria).
  
• The name of the medication and preparation.
  
• Whether this was the first exposure to the medication.
  
• How many doses were given before a reaction occurred.
  
• The time of onset of the reaction from the last dose given.
  
• The symptoms of the reaction and its total duration.

There are two main types:

Type A adverse drug reaction

• These are predictable from the known pharmacology of the drug and are dose dependent.
  
• Examples include opiate sedation and tachycardia with â2-agonists.

Type B adverse drug reaction

• These are less common, unpredictable (idiosyncratic) and dose-independent.
  
• They are often serious and usually require ceasing the drug, e.g. Stevens–Johnson syndrome (most commonly associated with anticonvulsants).

• Relatively few drugs need therapeutic drug monitoring.
  
• It is beneficial in drugs with a narrow therapeutic index, or where serum levels are well-correlated with efficacy or toxicity.
  
• Therapeutic drug monitoring can be useful for:

– Antibiotics, e.g. gentamicin, vancomycin.

– Anticonvulsants, e.g. phenytoin, phenobarbitone.

– Immunosuppressants, e.g. tacrolimus, cyclosporin, methotrexate.

– Drug overdose, e.g. paracetamol, iron.

• Routine testing is not beneficial for:

– Carbamazepine.

– Valproate.

• Timing of samples for monitoring will vary depending upon the actual drug but accurate recording of the drug dose, administration time and sample time is essential.

• Paediatric patients are at high risk of drug errors.
  
• Certain drugs are commonly associated with medication errors in children (e.g. opiates, paracetamol, antibiotics, 50% dextrose and electrolytes such as i.v. Ca²⁺ and Mg²⁺). Extra care should be taken when prescribing or administering these medicines.
  
• When prescribing for children, the following factors should be taken into consideration:

– Children’s doses vary widely and so there is no standard dose (as there is with adults).

– Clarify if drug doses are given in mg/kg per day in divided doses (or mg/kg per dose given x times per day).

– Calculations are required for most childhood dosing and errors may occur during this step.

– Some paediatric preparations may cause confusion in those unfamiliar with their use, e.g. i.v. versus enteral paracetamol, or Painstop Night-Time which contains three active agents.

– The small doses used in children may cause measuring and administration errors. – Misplacing or misreading of decimal points can lead to error.

• Drug interactions are always possible when using more than one medicine.
  
• Only a few drug combinations result in clinically significant sequelae.
  
• Be aware that drug interactions are more common when:

– More drugs are prescribed – where possible, aim for monotherapy.

– Patients are sick, especially with multiple organ pathologies.

• Drugs with a narrow therapeutic window are more likely to result in more significant interactions.

Specific history of these should be sought, as:

• Complementary medicines and many herbal products are available ‘over the counter’ or through alternative medicine practitioners.
  
• Families often do not offer this information.
  
• Such products can be involved in adverse drug reactions and interactions.

Examples of potential drug interactions

• St John’s wort: anticoagulants, antidepressants, digoxin, MAO inhibitors, dextromethorphan, decreases effects of cyclosporin and antiviral drugs, and prolongs effect of general anaesthetics.
  
• Ginseng: anticoagulants, stimulants, antihypertensives, antidepressants, phenelzine, digoxin, potentiates effects of corticosteroids and oestrogens.
  
• Ginger: anticoagulants, antihypertensives, cardiac drugs, hypoglycaemic drugs and enhances effects of barbiturates.