Watchful dosing of morphine or morphine equivalent dosing in the treatment of chronic non-cancer pain

The Canadian guideline for safe and effective use of opioids for chronic non-cancer pain by the National Opioid Use Guideline Group (NOUGG) was published in 2010 and defines a watchful dose of morphine or equivalent as being in excess of 200 mg/day. The American Pain Society and American Academy of Pain Medicine similarly identify high dose opioid therapy as constituting a total daily oral morphine (or equivalent) dose above 200 mg in their opioid treatment guidelines for chronic non-cancer pain (CNCP). Although not explicitly stated in the Canadian guidelines, the reason for establishing a threshold dose would appear to have arisen at least in part out of concern over the rising pattern of opioid prescribing that has occurred during the past ten years in Canada and its particular association with overdose and death. The 'watchful dose' would seem to act as an alert for clinicians contemplating exceeding this threshold to first reassess pain (including potentially, diagnosis), response to opioid therapy, risk for drug-related aberrant behaviors, among other issues such as health status and adherence, before proceeding. What is less clear for policymakers, however, is whether there are important public health safety concerns at morphine-equivalent doses below 200 mg/day. The present review therefore sought to examine the available safety evidence base for the 200 mg/day watchful morphine (or equivalent) dose in comparison to doses below this threshold.