Critical Dose Medicines And Brand Substitution: Issues With Anti-epileptic Drugs

February 9, 2009 at 11:00 am Leave a comment

Doctors and pharmacists are urged to exercise care when considering brand substitution for anti-epileptic drugs used for epilepsy, even if they are listed as bioequivalent on the Pharmaceutical Benefits Scheme.

Questions have been raised with NPS about whether brands of anti-epileptic drugs used for epilepsy should be substituted. Patients have also reported being offered alternative brands by pharmacy staff despite the ‘brand substitution not permitted’ box being checked.

“Once a patient’s epilepsy is under control, the brand of medicine they are prescribed should not be changed,” NPS CEO, Dr Lynn Weekes said.

“While the risk of loss of seizure control or toxicity arising from brand substitution is considered small and the evidence uncertain, the ramifications of loss of seizure control for some patients can be severe and therefore warrants avoidance.”

In its position statement, the Epilepsy Society of Australia recommends that ‘patients with epilepsy should first obtain the advice of their treating doctor before having the preparation of anti-epileptic drug interchanged’.

PBS-listed generic brands exist for several anti-epileptic drugs, including sodium valproate and carbamazepine. Examples of other critical dose medicines, i.e. medicines with a narrow therapeutic index, include warfarin, cyclosporin and digoxin.

“NPS encourages pharmacists to support patients using anti-epileptic drugs and other critical dose medicines by providing appropriate information about brand substitution, avoiding offering brand substitution at prescription intake and if necessary, referring the patient back to their prescriber,” Dr Weekes said.

Pharmacists and pharmacy staff are reminded that where the ‘brand substitution not permitted’ box is checked by the prescriber, brand substitution should not be offered at the time of prescription intake as this causes confusion for the consumer.

For further information about bioequivalence, critical dose medicines and brand substitution visit

The National Prescribing Service Limited (NPS) is an independent, non-profit organisation for Quality Use of Medicine funded by the Australian Government Department of Health and Ageing.

National Prescribing Service Limited



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