The most potent and longest acting anaesthetic agent is:
Dubucaine is the most potent, most toxic , and longest acting local anesthetic Cinchocaine or dibucaine is an amide local anesthetic. Among the most potent and toxic of the long-acting local anesthetics, current use of cinchocaine is generally restricted to spinal and topical anesthesia. From KD Tripati 7th edition Page no 367
Dibucaine
Tetracaine
Bupivacaine
Lignocaine
Anesthesia