[Present status of the use of adjuvant analgesics in Japan]

Adjuvant analgesics are drugs that have primary indications other than pain but are analgesic in selected circumstances. Antidepressants, anticonvulsants, local anesthetics, and NMDA receptor antagonists are drugs used in the treatment of neuropathic cancer pain. Assessment of pain is very important in selecting appropriate adjuvant analgesics. The assessment includes visual analog scale for pain intensity, McGill Pain Questionaire for quality of pain, and the location of pain. It is also important to assess the effectiveness of immediate release opioids. Most neuropathic pain is thought to be refractory to opioids. In Japan, effective adjuvant analgesics such as gabapentin and pregabalin are not available. The main adjuvant analgesics are still tricyclic antidepressants such as amytriptylin and amoxapin, and anticonvulsants such as carbamazepin and clonazepam. Another problem is that morphine is the only rescue drug available for the assessment of opioid responsiveness since morphine is the only opioid with an immediately release form among the strong opioids available in Japan which are morphine, oxycodone, and fentanyl. Adjuvant analgesics also have side effects such as constipation and sleepiness, which may augment the side effects of morphine and may impair the QOL of cancer patients with neuropathic pain. There is a need to improve the systems of development and importation of adjuvant analgesics.