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, – The article, 'Frequently asked questions about generic medicines' (Aust Prescr 2007;30:41-3), provides a clear and useful precis of some of the key issues that can impact on the decision to substitute an equivalent generic medicine.
However, the question of whether or not to substitute a medicine with a narrow therapeutic index with a bioequivalent generic remains open to debate. Perhaps the prescriber and pharmacist could approach this decision with more confidence if we consider the criteria used to define the term narrow therapeutic index, or more correctly narrow therapeutic ratio, by regulatory agencies.
The US code of federal regulations (Part 320.33(c) - Bioavailability and bioequivalence requirements) defines a medicine displaying a narrow therapeutic ratio as follows:
There is less than a 2-fold difference between median lethal dose and median effective dose
There is less than a 2-fold difference between minimum toxic concentrations and minimum effective concentrations in the blood
Safe and effective use of the drug products requires careful dosage titration and patient monitoring.1
The US Food and Drug Administration (FDA) specifically mentions only five medicines falling into this category, namely digoxin, lithium, phenytoin, theophylline and warfarin. However, the FDA recommends that even medicines with narrow therapeutic indices may be evaluated for bioequivalence using the conventional confidence interval limits of 0.80 to 1.25.2
In reality, the number of medicines matching the definition of narrow therapeutic ratio is very small indeed. In clinical practice, the dosage and plasma concentration of these medicines is usually carefully titrated and monitored.
Alphapharm Pty Ltd
Letter to the Editor
Editor, – I note that the problem of generic medicines has been mentioned again in your April edition (Aust Prescr 2007;30:41-3).
I am a firm believer in not using generic names - not from habit, but from practicality. When a drug is marketed the makers go to a lot of trouble to find a name that is easily recognised and remembered and unlikely to be confused with other drugs. The same cannot be said about generic names which are often complicated chemical names and the possibility of confusion arises.
John B Walker
Ear, Nose and Throat Specialist
The Editorial Executive Committee believes that the use of generic names in Australian Prescriber is appropriate. There are several reasons for this.
1. Medical students are not taught brand names, so it is appropriate that educational material uses generic names.
2. There are many different brand names for commonly prescribed drugs. It would be impractical to include all the brand names of each drug mentioned in Australian Prescriber.
3. The variety of brand names can cause confusion. There is a possibility of medication error with badly written prescriptions for drugs such as Losec and Lasix, Mobilis and Movalis, MS Contin and Oxycontin, Provera and Proviron.
4. The brand names are devised as part of a drug company's marketing strategy. As Australian Prescriber is independent of the pharmaceutical industry it avoids brand names.
5. Many thousands of people overseas visit the Australian Prescriber website. As brand names vary from country to country it is helpful if the articles use internationally approved names.
While the Editorial Executive Committee appreciates other views, generic names will continue to be used inAustralian Prescriber.
- Williams RL. FDA position on product selection for 'narrow therapeutic index' drugs. Am J Health Syst Pharm 1997;54:1630-2.
- http://www.fda.gov/cder/news/ntiletter.htm [cited 2007 Jul 10]
- Benet LZ. Relevance of pharmacokinetics in narrow therapeutic index drugs. Transplant Proc 1999;31:1642-4.