The Editorial Executive Committee welcomes letters, which should be less than 250 words. Before a decision to publish is made, letters which refer to a published article may be sent to the author for a response. Any letter may be sent to an expert for comment. When letters are published, they are usually accompanied in the same issue by their responses or comments. The Committee screens out discourteous, inaccurate or libellous statements. The letters are sub-edited before publication. Authors are required to declare any conflicts of interest. The Committee's decision on publication is final.
Letter to the editor
Editor, – I read with interest the article by Professor Birkett on generics (Aust Prescr 2003;26:85-7). However, the recent introduction of a generic form of the immunosuppressive drug cyclosporin confuses one of the key messages.
The abstract of the article states, 'There are no generic formulations of drugs with a narrow therapeutic index as it would be difficult for them to meet the required standard of bioequivalence'. The body of the article then explains why there are no generic forms for drugs such as digoxin and phenytoin where the dose is critical. It is therefore difficult to understand the reasoning behind the current situation with cyclosporin. This is arguably the most critical dose drug on the market. The fine balancing act between immunosuppressive efficacy and nephrotoxicity (and other dose-dependent adverse effects) is perhaps the most challenging part of practice for transplant clinicians, and requires careful and frequent monitoring of drug concentrations. The use of cyclosporin is further complicated by numerous significant drug interactions.
The generic form of cyclosporin seems to invalidate a key message in Professor Birkett's article and has left this reader confused. Generic forms of established medications have an important place in the Australian market, however, clinicians and consumers need to be very aware of the need for careful monitoring when a generic form of a 'difficult' drug such as cyclosporin becomes available. It is critical to minimise interchange between formulations without clear awareness by all parties involved in the patient's care.
Royal Adelaide Hospital
Editor, – In the article 'Generics - equal or not' (Aust Prescr 2003;26:85-7), Professor Birkett mentions that '...there are no generic products in Australia, for example, for digoxin...' Unfortunately there is! There is a generic of digoxin called Sigmaxin/Sigmaxin PG made by Fawns and McAllan which is available on the Pharmaceutical Benefits Scheme. I have not had a look at the tablets to see how similar they are to Lanoxin/Lanoxin PG and as I have recently come back from overseas, I am not sure how long they have been available.
Maureen M. Hendry
Quality Medication Care Clinical Pharmacy Services
Editor, – The recent article by Professor Birkett (Aust Prescr 2003;26:85-7) was an interesting contribution to the debate on generic drugs. However, we wish to point out a serious flaw in the argument for patients with chronic paroxysmal diseases like epilepsy. Generics are licensed for use if they show acceptable bioequivalence in short-term pharmacokinetic studies. We have no argument with this standard for drugs used to treat short-lived conditions, often using supra-therapeutic doses, such as antibiotics for bacterial infection. Similarly, for chronic conditions like hypertension or diabetes where there is a physiological marker that is a continuous variable, minor dosage adjustments can easily be made using a generic without adverse clinical consequences even if bioequivalence is imperfect.
In contrast, epilepsy is characterised by a state where the patient is apparently physiologically normal with seizures punctuating their lives in an episodic and unpredictable manner. Issues related to antiepileptic drugs are often identified as the cause for unpredictable seizures, including poor absorption associated with intercurrent infection, other drugs, diarrhoea or non-compliance. The type of evaluation done for generics to establish bioequivalence simply does not match what is required for conditions with a narrow therapeutic window such as epilepsy. There are many uncontrolled and anecdotal reports of patients having breakthrough seizures on changing from one form of an antiepileptic drug to another.1,2 Unfortunately, because of the nature of the problem, it is difficult to plan rigorous clinical trials to test the frequency and severity of such adverse events.3
We have no problem with the use of generic antiepileptic drugs, if a patient uses the same formulation continuously. However, the principle that patients requiring chronic therapy can be safely switched from one formulation of the drug to another, based on short-term bioequivalence studies, is a view that we cannot endorse. The consequences of a single seizure in an otherwise controlled patient can be devastating in terms of loss of driving licence, loss of job, physical injury or even loss of life. The temptation for the patient to take the cheaper alternative, often without the doctor's knowledge, needs to be corrected. The importance of this issue should be reinforced by the prescribing doctor and other healthcare professionals, particularly pharmacists.
Samuel F. Berkovic
Epilepsy Research Institute
University of Melbourne
President, Epilepsy Society of Australia
Frank J.E. Vajda
Australian Centre for Clinical Neuropharmacology
Raoul Wallenberg Centre
Chair, Standing Committee on Antiepileptic Drugs
Epilepsy Society of Australia
- Crawford P, Hall WW, Chappell B, Collings J, Stewart A. Generic prescribing for epilepsy. Is it safe? Seizure 1996;5:1-5. 2. Guberman A, Corman C. Generic substitution for brand name antiepileptic drugs: a survey. Can J Neurol Sci 2000;27:37-43. 3. Lesser RP, Krauss G. Buy some today: can generics be safely substituted for brand-name drugs? Neurology 2001;57:571-3 .