This study was performed in order to determine concentration-effect, and graded and quantal dose-response relationships for the clinical administration of intravenous (IV) lidocaine to patients with neuropathic pain. Thirteen patients were administered 500 mg of IV lidocaine at a rate of 8.35 mg/min over 60 min. Visual analog pain scores and venous blood samples were obtained concomitantly at 10 min intervals for 60 min. Blood samples were also obtained for determination of serum and serum water lidocaine concentrations at the onset of analgesia and at the time complete pain relief was attained. Lidocaine concentrations were determined by gas chromatography. Graded dose-response curves were prepared individually and for the group as a whole, and a quantal dose-response curve was prepared for the entire group. The dose-response relationship for IV lidocaine was characterized by large increases in pain relief for concomitant minimal increases in dosage. The difference between the ED50 (372.0 mg) and the ED90 (416.5 mg) was 44.5 mg of lidocaine (5.3 min of infusion). The concentration-effect relationship was also steep with pain scores abruptly decreasing over a range of 0.62 microgram/mL of lidocaine. Interestingly, the free concentration of lidocaine had no better correlation with the onset of analgesia or the attainment of complete analgesia than the serum concentration of lidocaine. This suggests that the mechanism of analgesia to IV lidocaine may not be based upon a conventional concentration-effect relationship. In conclusion, the results of this study suggest that the analgesic response to IV lidocaine is best characterized by a precipitous "break in pain" over a narrow dosage and concentration range.

Background and Aims Data on adequacy of EUS guided biopsies using different tissue acquisition techniques and fine needle aspiration needle designs have been inconclusive. Data on newer fine needle biopsy (FNB) needles are scarce. This study compared the performance of 3 acquisition techniques and 2 fine needle biopsy designs in solid pancreatic lesions. Methods Single-center, randomized, pilot clinical trial (Trial registration number NCT03264092). Patients undergoing EUS biopsy of pancreatic lesions were randomized to 1 of 3 acquisition techniques (dry suction, wet suction, slow pull) and 1 of 2 22G FNB needle designs. The primary outcome was specimen cellularity. Secondary outcomes included blood contamination and number of passes needed for diagnosis. Results A total of 52 (35.3%), 49 (33.3%) and 46 (31.3%) specimens were obtained with slow pull, dry suction and wet suction, respectively. A total of 56 (38%) and 91 (62%) specimens were obtained with each needle, respectively. No difference in cellularity scores was identified by technique (3.28 vs 3.55 vs 2.94; p = 0.081) or needle type (3.45 vs 3.15; p = 0.19). The same was true for blood contamination and diagnostic pass. A diagnosis was reached after 3 passes in 51 patients (93%). Histological diagnosis was possible in 45 specimens (82%). No severe adverse events occurred. Conclusions Cellularity of pancreatic specimens obtained with FNB needles via EUS was not influenced by technique and needle design. Three passes were enough to obtain a histological diagnosis in most patients. Larger clinical trials are required to validate the results of this study.

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