Alfentanil

Alfentanil (R-39209, trade name Alfenta, Rapifen in Australia) is a potent but short-acting synthetic opioid analgesic drug, used for anaesthesia in surgery. It is an analogue of fentanyl with around one-fourth to one-tenth the potency, one-third the duration of action, and an onset of action four times faster than that of fentanyl.[2] Alfentanil has a pKa of approximately 6.5, which leads to a very high proportion of the drug being uncharged at physiologic pH, a characteristi... [wikipedia]