Alfentanil
Chemical
Synthetic opioid of PHENYLPIPERIDINE CLASS
Ultrashort onset, short acting
Use
- Analgesia
- Blunt CV response to laryngoscopy
Presentation
2mg ampoule → 0.5mg/mL
Clear, colourless
pKa 6.5 → 90% UNIONISED pH 7.4
* crucial to rapid onset → UNIONISED crosses BBB *
Partition coefficient 130 → much less lipid soluble cf. F → but huge UNIONISED 90% ∴ large proportion of dose can cross BBB → ↑ speed
Dose
x 10 potency of Morphine
- Intubation = 15mcg/kg
- Analgesia = 5 – 50mcg/kg
- Infusion = 0.5 – 1mcg/kg/min
Onset / DoA
Peak 90 secs
DoA 5 – 10mins
MoA
µ-OP +++
k-OP ++
PD
CNS
- Analgesia
- Miosis
- ↓IOP
CVS
- CV stable
- Bradycardia
GU
- ↑smooth m. contraction
- Ureter, bladder
PK
A
–
D
PPB 92%
α1 acid glycoprotein
VD 0.86L/kg
Low lipid solubility & high PPB keeps it in central compartment
M
Liver
V. efficient
Cleared from plasma in 60 mins
PIPERIDIN N dealkylation to noralfentanil (majority)
AMIDE N dealkylation to N phenylpropionamide
E
<0.5% excreted unchanged in urine
Adverse Effects
- Resp D → APNOEA *monitor*
- Bradycardia
- N & V
- Dependence