Alfentanil

Chemical

Synthetic opioid of PHENYLPIPERIDINE CLASS

Ultrashort onset, short acting

Use

  1. Analgesia
  2. 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

Halft Times

  • Elimination t ½ : 1.6hrs
    • Shorter cf. F because its VD is so small
B
  • C5HT
    • Although alfentanil has short t ½
    • C5HT = 60 min (which is longer cf. sulfentanil)
    • ∴ is the better choice with quicker effect + prolonged infusion time