Effect of Opioids in Neuropathic Pain in Postherpetic Patients

Postherpetic neuralgia (PHN) is often associated with pain and sensory changes and is the leading type of neuropathic pain in modern clinical pain research. It is characterized by a variety of sensory patterns, which may be categorized into "irritable nociceptor" and "impairment of nociceptor". At date, several lines of evidence lead to the assumption, that mechanical hyperalgesia in PHN is based - at least in part - on central nervous processes of sensitization. In animal studies the investigators have discovered a previously unrecognized effect of opioids, the reversal of long-term potentiation (LTP) at C-fibre synapses, i.e. an opioid-induced depotentiation. In principle, synaptic depotentiation may be permanent or transient. In our study the clinically used ultra-short acting MOR agonist remifentanil normalized synaptic strength after wash-out of the drug. At present it is not known whether opioid-induced depotentiation can be used to the benefit of pain patients. The aim is to study the hypothesis, that pain in a group of PHN patients with predominant mechanical hyperalgesia is reversed by intravenous remifentanil at a plasma target concentration of 18ng/ml (corresponding to about 0.75 µg/kg/min) for 60 minutes compared with PHN patients of other sensory types.