Alfentanil

Question 1

Which class of opioid is Alfentanil

Answer 1

synthetic phenylpiperidine derivative

Question 2

Outline the pharmaceutical aspects

Answer 2

Presented as a colourless solution containing 500mcg/mL

Available as either 2 or 5mL vials

Question 3

What is the pKa and why is this significant

Answer 3

6.5
90% unionised at pH 7.4
10x more unionised drug is available at physiological pH
Rapid transfer across blood brain barrier -> very fast onset of action, and short lived response

Question 4

How much is protein bound

Answer 4

90%

Question 5

What is the morphine equivalence

Answer 5

10x more potent than Morphine

1mg of Alfentanil = 10mg Morphine

Question 6

What is the morphine equivalent lipid solubility

Answer 6

90x more lipid soluble than Morphine

Question 7

What is the volume of distribution

Answer 7

0.6L/kg

Question 8

What is the peak effect time

Answer 8

90 secs (1 1/2 mins)

Question 9

Outline the metabolism and excretion

Answer 9

Hepatic metabolism by CYP3A4 N-demethylation to Noralfentanil
(inactive)
Renal excretion

Question 10

What is the elimination half time

Answer 10

100 mins

Question 11

What are the advantages of Alfentanil

Answer 11

Low pKa equating to high amount of unionized drug available at physiological pH = very rapid onset
Shorter context sensitive half time cf Fentanyl
10% 1st pass pulmonary epithelial uptake (lower than Fentanyl)
No significant histamine release
Inactive metabolites

Question 12

What is the dose of Alfentanil

Answer 12

Induction 7-15mcg/kg

Brief analgesia while ventilated - upto 50mcg/kg