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Serotonin noradrenaline reuptake inhibitors: A new generation of treatment for anxiety disorders

A variety of agents are currently used to treat the different anxiety disorders. Benzodiazepines, such as diazepam, are still preferred by some for the treatment of acute anxiety, with the advantage of a rapid onset of action, but they are less suitable for long-term treatment due to their potential for memory disturbances, sleepiness, lethargy, physical dependence and withdrawal. Compounds acting on monoamine neurotransmission are more suitable in the treatment of long-term or chronic anxiety disorders. Tricyclic antidepressants, such as imipramine, and monoamine oxidase inhibitors have been shown to be effective anxiolytics, but their side effects and safety concerns have limited their use. The probable role of disturbed serotonergic neurotransmission in anxiety is widely accepted and is the theoretical basis for the use of serotonergic agents such as the 5-HT1A receptor partial agonist, buspirone, and the selective serotonin reuptake inhibitors (SSRI), such as sertraline and paroxetine, which have largely replaced the earlier antidepressants. There is clear evidence for decreased serotonergic function in anxiety as well as in depression. Studies of patients with anxiety disorders show reduced levels of serotonin in cerebrospinal fluid (CSF) as well as reduced serotonin transporter binding. The role of noradrenaline in the control of anxiety is less well understood, although there is considerable evidence to suggest that a disturbance of noradrenergic neurotransmission may also contribute to the symptoms of anxiety. Noradrenaline modulates the activity of brain regions such as the amygdala which are associated with anxiety. In addition, anxiety states are associated with increases in the metabolite of noradrenaline, 3-methoxy-4-hydrophenylglycol (MHPG), and hypersecretion of noradrenaline in plasma and CSF. It appears likely that modulation of both serotonin and noradrenaline systems by dual-reuptake inhibitors may prove to be an advantage in the treatment of anxiety disorders. The serotonin–noradrenaline reuptake inhibitors (SNRI), venlafaxine, milnacipran and duloxetine are efficacious in relieving anxiety symptoms within depression, and some have proven efficacy in certain anxiety disorders. Initial studies suggest that dual acting agents may have an advantage over selective reuptake inhibitors in certain anxiety disorders, such as post-traumatic stress disorder (PTSD), and in patients with comorbid anxiety and depression.