The Minimal Clinically Important Difference In Efficacy Trials Of Analgesics

The objective of analgesic medication is to relieve discomfort and ameliorate the patient’s dissatisfaction with his/her overall clinical state related to pain. Because pain can be perceived only by the patients/subjects themselves, subjective patient reports are the only measures of pain intensity currently available. Even if an objectively measurable physiologic variable correlated with the neurologic basis of pain could be established, the perceived level of discomfort and the dissatisfaction associated with a given “physiologic level” of pain would likely vary widely between individuals and in differing circumstances for a given individual. Therefore, various patient-reported outcomes (PROs) will likely remain the gold standard measures in clinical trials for analgesics.

Statistical analysis methods can assess the likelihood that an improvement in the score on a PRO pain scale after treatment with an analgesic could be due to chance, but they do not indicate whether the magnitude of the improvement would be meaningful to patients. Small differences may be statistically significant, but not indicative of a change in pain intensity which many individuals would consider important and worth the expense and possible risks associated with taking that medication. Therefore, for trials of the efficacy of analgesics, it is necessary to determine the smallest change in a PRO pain scale score that would be considered important by patients, i.e., the minimal clinically important difference (MCID). Participants who have improvements of magnitude equal to or greater than the MCID are classified as “responders”.