Siriwardena et al1 in their article move from their initial assertion of a ‘lack of evidence distinguishing short-acting benzodiazepines and the newer Z-drug hypnotics’ in their introduction; to an implied assertion in the title of their article and in the paragraph ‘how this fits in’ that there is evidence that there is no difference. A lack of evidence is not the same as evidence of no difference.
Indeed the NICE appraisal2 of this subject pointed to a need for research in this area, and also highlighted the reality that it was unlikely to occur.
In pharmacology training doctors are taught about half-lives, this was the argument put forward in the past for using less of, for example, nitrazepam as hypnotics. Z-drugs have significantly shorter half lives than short-acting benzodiazepines, it is not surprising then that GPs believe that Z-drugs cause less ‘daytime sleepiness/sedation’. In situations where evidence is lacking doctors will be influenced by guidelines, by their own experience, by their understanding of pharmacology, and, yes, by those who seek to influence their prescribing.
While it is true that the trend in hypnotic prescribing is not evidence based, it is not true that it goes against the evidence. The evidence is simply not there. This is an important axiom in evidence-based medicine.
- © British Journal of General Practice, 2007.
