Antiepileptic drugs categorised to help prescribers avoid switching risks
New guidance on prescribing antiepileptic drugs (AEDs) has been issued by the Medicines and Healthcare products Regulatory Agency because of the potential risks from switching between branded and generic products or between different generic products.
The agency said that, although there was no clear evidence of harm, an effect in some patients for some drugs could not be ruled out. Risks potentially associated with changing products include loss of seizure control and other side effects, the MHRA says in a statement issued following a safety review conducted by its Commission on Human Medicines.
The MHRA has now classified all AEDs into three categories — numbered 1, 2 and 3 — to help prescribers and patients decide whether it is necessary to maintain continuity of supply of a specific product. Drugs have been grouped according to their therapeutic index, solubility and absorption.
Category 1 is for phenytoin, carbamazepine, phenobarbital and primidone, for which prescribers are advised to ensure that patients are maintained on a specific manufacturer’s product.
Category 2 includes drugs where the need for continued supply of a particular manufacturer’s product should be based on clinical judgement and consultation with the patient or carer. Prescribers should take into account factors such as seizure frequency and treatment history. The AEDs in this category are: valproate, lamotrigine, perampanel, retigabine, rufinamide, clobazam, clonazepam, oxcarbazepine, eslicarbazepine, zonisamide and topiramate.
Category 3 covers levetiracetam, lacosamide, tiagabine, gabapentin, pregabalin, ethosuximide and vigabatrin. This category contains drugs where it is usually unnecessary for patients to be maintained on a specific manufacturer’s product, unless there are concerns relating to patient anxiety, and risk of confusion or dosing errors.
In a letter to health care professionals, CHM chairman Stuart Ralston issues specific advice for pharmacists. He writes: “Dispensing pharmacists should ensure the continuity of supply of a particular product when the prescription specifies it. If the prescribed product is unavailable, it may be necessary to dispense a product from a different manufacturer to maintain continuity of treatment of that AED. Such cases should be discussed and agreed with both the prescriber and the patient (or carer).”
Usual prescribing practice should be followed when a specific product is not requested, he advises.
Citation: The Pharmaceutical Journal DOI: 10.1211/PJ.2013.11130148
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