<prompt> Longest acting L.A. a Bupivacaineb Tetracainec Xylocained Procaineacaadab  <response>: Dibucaine is the longest acting LA duration is 2.5-3.5 hours.Amongst the given options tetracaine bupivacaine are longest acting both have duration of 2-3 hours.Decreasing order of duration :- Dibucaine longest acting Bupivacaine Tetracaine Ropivacaine Etidocaine Prilocaine Lignocaine Mepivacaine Cocaine Procaine chlorprocaine. 