We retrospectively evaluated the long-term effects of selective nerve root block in patients with lumbosacral monoradiculopathy associated with failed back surgery syndrome, lumbar disc herniation and lumbar spinal stenosis. We analyzed 72 patients including 27 patients with failed back surgery syndrome, 23 patients with lumbar disc herniation and 22 patients with lumbar spinal stenosis. Patients received selective nerve root block under fluoroscopy. Numerical Rating Scale (NRS: 0-10) and non-steroidal anti-inflammatory drugs (NSAIDs) consumption were analyzed to evaluate of pain relief. In all groups, NRS and NSAIDs consumption decreased significantly 1 and 3 months after nerve root block compared to the baseline. In the lumbar disc herniation group, NRS and NSAIDs consumption were the lowest among the three groups at 1 and 3 months. There were no significant differences in NRS and NSAIDs consumption between failed back surgery syndrome and lumbar spinal stenosis. These findings show that selective nerve root block for lumbar disc herniation induces superior a long-term pain relief for lumbosacral radiculopathy compared with those for failed back surgery syndrome and lumbar spinal stenosis. The pain relief for Failed back surgery syndrome was similar to that for lumbar spinal stenosis 3 months post treatment.

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Ketamine is an N-methyl-D-aspartate receptor antagonist widely used as an anesthetic. The subanesthetic dose of ketamine has been reported to have an analgesic effect. Since ketamine is currently not commercially available except in an injectable form in Japan, several pharmaceutical preparations of ketamine for oral administration have been proposed for hospital use. Previously, we described a new pharmaceutical preparation of ketamine using agar, ketamine Agar-Gel. In the present study, we examined the analgesic effect and plasma concentration profiles of ketamine Agar-Gel when buccally administrated to a patient with postherpetic neuralgia. Pain intensity was measured using a numerical rating scale (NRS). Furthermore, we determined the plasma concentrations of ketamine and norketamine after administration of ketamine Agar-Gel. When ketamine Agar-Gel was administered, the pain intensity was reduced to 33-86% of the previous level and the effect lasted 3-4 hours. Two months after administration of the preparation, the pain resolved and no further treatment was required. The plasma concentration profile of ketamine and norketamine after buccal administration of ketamine differed from that after oral administration of ketamine reported previously, while the plasma concentrations of norketamine were almost the same as those of ketamine. We will examine the usefulness of ketamine Agar-Gel in additional cases.

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[in Japanese]

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Ketamine has been widely used for analgesia in patients with neuropathic pain. However, only injectable forms of ketamine are commercially available in Japan. We have previously reported a new oral preparation of ketamine, the ketamine Agar-Gel. In the present study, we examined the pharmacokinetic characteristics of ketamine and norketamine after oral administration of the Agar-Gel in comparison with those after buccal administration. Four healthy volunteers were given the ketamine Agar-Gel orally or buccally in random order. Venous blood samples were obtained before and up to 6 hour after administration, and plasma concentrations of ketamine and norketamine, a metabolite form of ketamine, were measured by high-performance liquid chromatograph. The plasma concentration of norketamine was significantly higher than that of ketamine after oral administration (p<0.05). The AUC_0→6h value of ketamine after buccal administration was about twofold higher than that after oral administration, while the AUC_0→6h of norketamine after buccal administration was lower than that after oral administration. These results indicate that the extensive first-pass metabolism of ketamine would be inhibited by the buccal route.

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