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Ketamine, an N-methyl-D-aspartate antagonist, reduces pain by decreasing central sensitization and pain windup. However, chronic ketamine use can cause tolerance, dependency, impaired consciousness, urinary symptoms, and abdominal pain. This study aimed to investigate the effects of repeated ketamine injections and ketamine readministration after discontinuation in a rat model of neuropathic pain. To induce neuropathic pain, partial sciatic nerve ligation (PSNL) was performed in 15 male Wistar rats, and these animals were divided into three groups: PSNL (control), PSNL + ketamine 5 mg/kg (K5), and PSNL + ketamine 10 mg/kg (K10; n=5 each). Ketamine was injected intraperitoneally daily for 4 weeks, discontinued for 2 weeks, and then readministered for 1 week. Following PSNL, the mechanical withdrawal threshold was determined weekly using the Von Frey. The K10 group showed a significant increase in the mechanical withdrawal threshold, presented here as the target force (in g), at 21 and 28 days compared to the time point before ketamine injection (mean±SE, 276.0±24.0 vs. 21.6±2.7 and 300.0±0.0 vs. 21.6±2.7, respectively; P2 weeks, but this ketamine effect decreased after drug readministration.

BackgroundIntravenous (IV) dexamethasone prolongs the duration of a peripheral nerve block; however, there is little available information about its optimal effective dose. This study aimed to evaluate the effects of three different doses of IV dexamethasone on the duration of postoperative analgesia to determine the optimal effective dose for a sciatic nerve block.MethodsPatients scheduled for foot and ankle surgery were randomly assigned to receive normal saline or IV dexamethasone (2.5 mg, 5 mg, or 10 mg). An ultrasound-guided popliteal sciatic nerve block was performed using 0.75% ropivacaine (20 ml) before general anesthesia. The duration of postoperative analgesia was the primary outcome, and pain scores, use of rescue analgesia, onset time, adverse effects, and patient satisfaction were assessed as secondary outcomes.ResultsCompared with the control group, the postoperative analgesic duration of the sciatic nerve block was prolonged in groups receiving IV dexamethasone 10 mg (P < 0.001), but not in the groups receiving IV dexamethasone 2.5 mg or 5 mg. The use of rescue analgesics was significantly different among the four groups 24 h postoperatively (P = 0.001) and similar thereafter. However, pain scores were not significantly different among the four groups 24 h postoperatively. There were no statistically significant differences in the other secondary outcomes among the four groups.ConclusionsThis study demonstrated that compared to the controls, only IV dexamethasone 10 mg increased the duration of postoperative analgesia following a sciatic nerve block for foot and ankle surgery without the occurrence of adverse events.