Medication adherence in patients with chronic non-malignant pain: Is there a problem?

Abstract

Kosmidou and colleagues made a constructive contribution to our review (Broekmans et al., 2009). They added three additional issues to consider, when studying adherence with analgesic treatment. First, how do we define adherence and compliance to treatment? Second, are adherence and compliance numeric or qualitative factors? And finally, there are no studies focusing on neuropathic pain, a common cause of chronic non-malignant pain. The authors underline once more an important gap in the adherence literature: how much adherence is needed in patients suffering chronic non-malignant pain? Until now, no evidence is available to support a specific cut off percentage of adherence. There are no studies on how adherent patients have to be to ensure positive outcomes. Giannopoulos et al. (2007) used a cut off of 75% to define adherence: patients taking less than 75% of their medication were considered non-adherent. However, the authors did not report on outcome differences between adherent and non-adherent patients. Hence, evidence supporting the choice of this cut-off is currently lacking. Prospective studies are needed to provide evidence on the relationship between adherence and clinical outcome. At the moment, there is no evidence in a chronic pain population supporting the cut off of 75%. In other populations, where adherence is of the utmost importance (e.g. patients prescribed antiretroviral therapy) a 75% cut off would be regarded as excessively low. A second major finding of our review was that in patients with chronic non-malignant pain, two different types of medication non-adherence emerge: underuse and overuse. It can be expected that underusers and overusers do have a different profile. Future research should therefore investigate determinants of underuse and overuse non-adherence separately. Overuse of medication was not taken into account in the study of Giannopoulos et al. (2007). Our own research (Broekmans et al., unpublished results) showed that irrespective of pain diagnosis, these two types of non adherence are present. Among patients suffering from neuropathic pain, 31–48% is underusing their pain medication; 4–20% of these patients are overusing pain medication. These percentages do not differ significantly from the under- or overuse prevalence in other chronic pain diagnoses (e.g. low back pain, fibromyalgia). We agree with Giannopoulos et al. that adherence in chronic pain patients should take into account the type of pain (e.g., neuropathic versus nociceptive) and the type of pain medication (e.g. typical versus atypical analgesics). In conclusion, there is need for prospective adherence research in chronic non-malignant pain populations to determine an adequate level of adherence with regard to outcome. Both overuse and underuse of pain medication should be assessed, as well as different types of chronic pain and pain medications.