Sum of Pain Intensity Differences (SPID) in migraine trials. A comment based on four rizatriptan trials

Sum of Pain Intensity Difference (SPID) is an outcome measure that summarizes treatment response over a clinically relevant period. SPID is widely reported in clinical trials of analgesics but has been little used in migraine trials. We compared SPID over 2 h with the standard migraine outcome measures of pain-free at 2 h and headache relief at 2 h using data from four published clinical trials of rizatriptan in migraine patients. In assessing treatment response (rizatriptan and sumatriptan versus placebo, rizatriptan versus sumatriptan, within-treatment dose effects), SPID usually yielded similar results to the more easily understood pain-free measure.