Pharmacological synergy: the next frontier on therapeutic advancement for migraine

The burden of migraine significantly impacts the individual sufferer, their families, the workplace, and society. The World Health Organization has identified migraine as an urgent public health priority and has initiated a global initiative to reduce the burden of migraine. Underlying the World Health Organization initiative is the need to discover means of optimizing migraine treatments and make them accessible to the broader portion of the world population. Development of acute migraine medications over the past several decades has largely centered on engineering highly specific receptor molecules that alter migraine pathophysiological mechanisms to abort or reverse the acute attack of migraine. The first product of this line of discovery was sumatriptan and heralded as a landmark therapeutic breakthrough. Sumatriptan is a 5-HT-1B/D receptor agonist considered to activate receptors involved in the pathophysiology specific to migraine. Large-scale regulatory/clinical studies demonstrated statistical superiority for sumatriptan over placebo in reduction or elimination of headache, nausea, photophobia, and phonophobia. Since the introduction of sumatriptan, 6 other triptan products have been released in the United States as acute treatments for migraine, all having the same mechanism of action and similar efficacy. Despite their utility as migraine abortive medications, the triptans do not successfully treat all attacks of migraine or necessarily treat all migraine associated symptoms. In fact, in less than 25% of attacks do subjects obtain and maintain a migraine-free response to treatment for at least beyond 24 hours. A wide range of non-triptan medications also have demonstrated efficacy in acute migraine. These include non-steroidal anti-inflammatory drugs (NSAIDs), opioids, phenothiazines, and valproic acid to name a few. Given the distinctly different mechanisms of actions of these various medications, it is likely that several unique pathophysiological mechanisms are involved in terminating acute episodes of migraine. Clinicians now capitalize on this observation and use migraine medication in combination with another to improve patient outcomes, for example, using an antiemetic with an opioid or a triptan and NSAIDs. More recently, the Food and Drug Adminstration has approved a combination product containing 85mg of sumatriptan plus 500mg of naproxen sodium for acute treatment of migraine. Clinical trials conducted prior to approval demonstrated that the combination of sumatriptan and naproxen was more effective as a migraine abortive than either of its components but that each component and the combination were more effective than placebo. Exactly how sumatriptan and naproxen interact to create therapeutic synergism is unknown though its mere occurrence suggests that models assisting medical understanding and prediction of pharmacological synergism may improve clinical outcome over products acting through a single receptor mechanism. Migraine is a syndrome, meaning it is defined by observed symptoms rather than known pathophysiology. Multiple pathogenic mechanisms are likely involved in generating this diverse array of symptoms understood as the migraine symptom complex. Sumatriptan and naproxen have independent mechanisms of action and target distinct aspects of the vascular and inflammatory processes hypothesized to underlie migraine. Sumatriptan acts on the 5-HT(1B) and 5-HT(1D) receptors, whereas naproxen inhibits the COX-1 and COX-2 enzymes. Sumatriptan has vasoconstricting effects as well as effects on neurogenic inflammation by decreasing the release of substance P and calcitonin gene-related peptide. In contrast, naproxen affects prostaglandins and other inflammatory mediators. Because sumatriptan and naproxen both relieve migraine yet interact with different cellular targets within the migraine pathway, it is reasonable to assume there is a unique synergy between these medications that improves treatment outcomes. Clinical trials supported this contention by demonstrating the combination of sumatriptan/naproxen alleviated migraine pain quickly (primarily based on the sumatriptan mechanism of action), and sustained the response longer (primarily based on the naproxen mechanism of action) than is possible when either drug is given alone. The working hypothesis is that when sumatriptan and naproxen are given at the same time, they affect different mechanisms of the migraine pathway and produce an enhanced therapeutic effect. The purpose of this article is to apply statistical analyses to data from phase II and phase III studies of the combination of sumatriptan and naproxen to determine if this enhanced therapeutic effect is synergistic. This methodology of accessing synergy can be used in the development of future combination migraine treatments to improve treatment outcomes.