The rational design of ultra-short-acting (USA) agents for use in critical care has been described for 8-blockers, 2 antiarrythmi~ s,~ and analgesic^.^ Their short duration of action is based on the inactive metabolite approachs whereby the active species is enzymatically degraded in vivo to less or inactive products. The advantages of these drugs over their longer actingcounterparts is that the short biological half-life-normally 10-15 min-provides, ...