Dose comparison of remifentanil and alfentanil for loss of consciousness.
BACKGROUND
This study evaluated the efficacy and safety of remifentanil, a potent mu agonist opioid with a rapid onset and offset of effect, as a sole induction agent for loss of consciousness (LOC) and compared it with alfentanil.


METHODS
Remifentanil and alfentanil were administered intravenously over 2 min in ascending doses (remifentanil 2, 3, 4, 5, 6, 8, 10, 15, 20 microg/kg; alfentanil 40, 60, 80, 100, 120, 160, 200 microg/kg) to unpremedicated healthy patients. Patients were observed for rigidity and LOC for 30 s after the end of infusion. If patients had not lost consciousness, 2 mg x kg(-1) x min(-1) thiopental was administered until LOC was achieved. Arterial blood samples, obtained at specified time intervals, were analyzed for remifentanil and alfentanil whole-blood concentration. Blood pressure and heart rate were also recorded at preset time intervals.


RESULTS
Neither drug could reliably produce LOC. With both drugs, there was a dose-dependent decrease in thiopental requirements and a dose-dependent increase in the incidence and severity of rigidity (P < 0.05). The median effective dose (ED50) for LOC with remifentanil was 12 microg/kg, and for alfentanil it was 176 mcrog/kg. The median effective concentration (EC50; whole-blood concentration) of remifentanil was 53.8 ng/ml and for alfentanil it was 1,012 ng/ml. Minimal hemodynamic changes were observed after either drug was given.


CONCLUSIONS
Remifentanil is 15 times more potent than alfentanil, based on the ED50 to achieve loss of response to a verbal command and 20 times more potent than alfentanil based on the EC50. Neither opioid is suitable as a sole induction agent.
Jhaveri
R
R
Department of Anesthesia, Duke University Medical Center, Durham, North Carolina 27710, USA.
Joshi
P
P
Batenhorst
R
R
Baughman
V
V
Glass
P S
PS
D000328:Adult; D000368:Aged; D015760:Alfentanil / Q000008:administration & dosage* / Q000009:adverse effects; D003243:Consciousness / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D008875:Middle Aged; D009127:Muscle Rigidity / Q000139:chemically induced; D010880:Piperidines / Q000008:administration & dosage* / Q000009:adverse effects; D000077208:Remifentanil
D010880:Piperidines; D015760:Alfentanil; D000077208:Remifentanil