Dr. David Lyness
Synthetic phenylpyperidine derivative structurally related to fentanyl; it has 10-20% of its potency.
Comes in vials such as 1mg/ml - colourless solution
Used in anaesthetic inductions and infusions in ICU
Agonist at MOP receptor
Introduced in 1980
10mcg/kg as bolus dose to attenuate laryngoscope reflex
0.5-2 mcg/kg/min infusion in ICU for sedation/ETT
Quicker onset to fentanyl and shorter duration of action - it moves out from the brain into other tissues rapidly
Much lower lipid solubility than fentanyl... (6-7x less)
Yet more alfentanil = unionised form compared to fentanyl (89% compared to 9%)= rapid onset
Less alfentanil is distributed to muscles and fat but...
Vd is relatively small and more of the dose remains in blood from which it can be cleared by the liver.
Alfentanil has a lower clearance rate, yet offset by its reduced Vd and its half life is relatively short.
1mg = 70p
Essentially VERY similar to FENTANYL but shorter duration (1/3) of action and 4x QUICKER onset
Alfentanil has a pKa of 6.5, which leads to a very high proportion of the drug being uncharged at physiologic pH.
Fewer CVS complications compared to other opioids, but more profound respiratory depression
Duration = 15mins
Onset = ~1.5mins
Half-life = 90-111min
92% Protein Binding
Numerous Inactive Metabolites
Compared to remifentanil, it has a variable context-sensitive half-life,
but is still more predictable than fentanyl with greater lengths of infusion....
GOOD CHOICE FOR SHORT CASES
GOOD POTENT ANALGESIA FOR SHORT BURST STIMULI