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Background and Objectives: Use of regional anesthesia can result in faster recovery and better patient satisfaction. Addition of perineural adjuncts to local anesthetics may improve the duration of analgesia, but there is a paucity of data comparing them in a single randomized trial. We compared the effects of three adjuncts clonidine, dexamethasone, and buprenorphine, on the duration of analgesia of interscalene brachial plexus block.Methods: 160 patients, undergoing elective shoulder surgery, were randomized to four groups to receive an interscalene block with one of the following solutions: ropivacaine alone, ropivacaine with clonidine 75 µg, ropivacaine with dexamethasone 8 mg, or ropivacaine with buprenorphine 300 µg. The primary outcome variable was the duration of analgesia; secondary outcome measures were time to onset of the block, and the duration of sensory and motor blocks.Results: There was no statistically significant difference in the total analgesia time among the four groups; p=0.11. The pairwise comparison in analgesic time and 99% CI were: control versus clonidine (-1.94 hours (-7.33 to 3.12)), control versus dexamethasone (-4.16 hours (-9.50 to 0.58)) and control versus buprenorphine (-1.1 hours (-5.34 to 3.23)). There was no differences in block set-up time, or total sensory and motor block duration among the groups.Conclusion: There was no significant improvement in the duration of analgesia with addition of any of the three adjuncts to interscalene blocks. However, there was a larger than expected variability in patient response, hence the study may have been underpowered for the primary outcome. [ABSTRACT FROM AUTHOR]