Warfarin, medicinal drugs and road traffic accidents

Abstract

Delaney et al . [1] have recently reported that warfarin use has not been linked to an increase in road traffic accidents as previously reported [2].The finding of no increase in the risk of motor vehicle accidents following warfarin use is reasonable, as there is no evidence that this medicinal drug impairs psychomotor performance. Furthermore, in the summary of product characteristics and package insert within the European Union (EU) it is not mentioned that this drug impairs driving performance, as the authors also indicated for Canada [1]. Within the EU, according to the existing rules, information about the effect of medicinal drugs on driving and the use of machinery should be included in the summary of product characteristics and package insert [3, 4]. Furthermore, a classification regarding the effects of drugs on driving performance has been proposed [5]. Spain introduced a three-level categorization system after Belgium, and warfarin was rated as a non-impairing medicinal drug of driving performance.One aspect of relevance is that, in the sample of the mentioned study [1], both the cases (78%) and controls (76%) were taking 'sedating drugs' quite frequently. Many of these drugs (benzodiazepines, barbiturates, classic antidepressants and antipsychotic drugs) have shown a clear deteriorating effect on psychomotor performance [6] and appropriate warnings appear in the summary of product characteristics and package inserts. They are frequently rated as category III (likely to produce severe effects) or II (likely to produce minor or moderate effects). Nevertheless, the new antidepressants (selective serotonin reuptake inhibitors and antipsychotic drugs) have a less impairing effect on driving performance and are classified as low impairing drugs. What is of relevance is that in clinical practice, when prescribing to a driver (the majority of the population in Western countries), appropriate drug selection and information regarding driving should be provided. An additional aspect to be considered, as mentioned by the authors [1], as well as in previous studies [5], is the possibility of interaction between the prescribed drugs, as well as with alcohol.Regarding the study design, the authors noticed [1] that they were not able to control by exposure (distance driven), which is a key issue. The question has also recently been raised that those drivers who drove less distance are more frequently involved in road accidents in any age group [7]. Alcohol consumption is another confusing factor for which results has not been controlled. Alcohol consumption varies according to age, decreasing as age increases but still frequent in older people [8]. This may be of relevance, as many of the subjects in the study were taking 'sedating drugs'.Within the EU policy of reducing road traffic accidents, the target is a 50% reduction between 2000 and 2010. To achieve this, the action programme is making continuing efforts 'to combat the scourge of drinkdriving and find solutions to the issue of the use of drugs and medicine...

Warfarin: almost 60 years old and still causing problems

“…However, the association between warfarin and road traffic accidents was not replicated in a recent study published in the Journal [19], and this is again emphasized in this issue [20]. Nevertheless, as Alvarez points out [21], assessment of whether drugs cause road traffic accidents is highly complex, and confounding by indication, concomitant medications, alcohol intake, and driving experience can all influence the findings. It is therefore not surprising that replication of initial findings is often difficult.…”