3 Such patients may have opioid-induced hyperalgesia, which can occur even after brief exposure to opioids.26 Furthermore, based on the premise that supporting

glia, their receptors, and their secreted mediators may play an important role in neuronal function regulation and so may contribute to migraine,27 Watkins and others have posited a mechanism whereby chronic morphine exposure may modulate glial function, suggesting that the clinical efficacy of opiates for pain control is limited by analgesic tolerance and hyperalgesia.28 A recent study pointed to common cellular mechanisms of opioid-induced desensitization and sensitization mediated through activation of the central glutamatergic system.29 Opioid tolerance and opioid-induced

hyperalgesia are distinct pharmacologic phenomena, but over time, each results in decreased effectiveness of a Histone Methyltransferase inhibitor given opioid dose, leading to dose escalation.25 In opioid-induced hyperalgesia, patients experience pain or increased sensitivity to pain even when serum opioid levels are low. Even at baseline (before the start of the opioid infusion), their pain tolerance is decreased compared to that of opioid-naive patients. In opioid tolerance, the administered dose is no longer effective and the dose must be increased to get the same effect. This reflects desensitization of patients’ antinociceptive pathways from chronic use of opioid medications; no change in pain sensitivity occurs at baseline. How Migraine Medications Work.— Five medications commonly find more used in migraine prophylaxis – topiramate, valproate, propranolol, amitriptyline, and methysergide

– have a common mechanism of action.30 Chronic administration of these 5 migraine preventive medications, Quisqualic acid but not the control L-propranolol, has been shown to reduce CSD in rats, suggesting that suppression of CSD is a common mechanism of action for migraine preventive medications. Ayata et al tested the hypothesis that all of these medications suppress CSD, implicated in migraine attacks. The investigators administered various doses of each of the 5 medications to male Sprague–Dawley rats. Prophylactic efficacy of the 5 medications positively correlated with duration of treatment. Chronic treatment with each of the 5 medications almost completely suppressed CSD after a 17-week course of treatment,30 whereas in human beings, a trial of at least 3 months may be necessary to determine the efficacy of those medications in migraine prevention.3 The study also showed that the efficacy of the medications is dose-dependent.30 Therefore, physicians should begin with a low dose and titrate the dose up when prescribing any of those medications for their patients with migraine.