Switching of anti-epileptic drugs (AEDs)
Epilepsy is a complex medical condition that has a variety of clinical manifestations, but in all cases it involves a change to the normal electrical conductivity in the brain. The result is a 'seizure' of one type or another which disrupts brain activity and can interrupt normal consciousness. Seizures have a significant impact on the health and well-being of epilepsy sufferers and the principle aim of pharmacological treatment is to prevent the occurrence of attacks whilst minimising the risk of side effects. Any factor that influences the likelihood of a seizure occurring could have a significant impact on a patient's quality of life.
Despite the existence of regulatory standards to demonstrate the bioequivalence of generic products, patients and prescribers have expressed concerns over their relevance to AEDs. It is felt that the bioequivalence test does not necessarily demonstrate clinical equivalence - different formulations of the same drug may not have the same clinical effect and switching between formulations could result in breakthrough seizures and other adverse events. There a number of reasons why these concerns may be valid; principally the relatively narrow therapeutic range of many AEDs coupled with the potentially serious consequences of therapeutic failure. Other important factors are the complex nature of drug-drug interactions with many AEDs and the low solubility and bioavailability of some AEDs.
In their clinical guidelines for epilepsy NICE recommends that patients receive the same manufacturer’s product unless this is deemed unnecessary by the prescriber and patient.2
NICE guideline 137:1.9.1.4
"Consistent supply to the child, young person or adult with epilepsy of a particular manufacturer's AED preparation is recommended, unless the prescriber, in consultation with the child, young person, adult and their family and/or carers as appropriate, considers that this is not a concern. Different preparations of some AEDs may vary in bioavailability or pharmacokinetic profiles and care needs to be taken to avoid reduced effect or excessive side effects."
The NICE guideline implies that should there be a need to switch between products, for instance due to a stock shortage, the prescriber and the patient, or their representative, should be consulted and agreement obtained. While this makes no reference to the dispensing pharmacist it is clear that consistent supply can only be achieved with pharmacy involvement.