Alfentanil

Alfentanil - It is an opioid 30 times more potent than morphine and its duration is shorter than that of fentanyl. The maximum effect occurs about 1 min after IV injection. Duration of action following an IV bolus is between 5 and 10 min. Its distribution volume and lipophilicity are lower than fentanyl. It is ideal for infusion and may be the agent of choice in renal failure.The context-sensitive half-life may be prolonged following IV infusion. In patients with hepatic failure the elimination half-life may be markedly increased and a prolonged duration of action may be seen.

Uses
Patients receiving short-term ventilation

Contraindications
Airway obstruction
Concomitant use of MAOI

Administration
• IV bolus: 500 μg every 10 min as necessary
• IV infusion rate: 1–5 mg/h (up to 1ug/kg/min)
Draw ampoules up neat to make infusion, i.e. 0.5 mg/ml or dilute to a convenient volume with glucose 5% or sodium chloride 0.9%

How not to use alfentanil:
In combination with an opioid partial agonist, e.g. buprenorphine (antagonizes opioid effects)

Adverse effects:
Respiratory depression and apnoea
Bradycardia
Nausea and vomiting
Delayed gastric emptying
Reduce intestinal mobility
Biliary spasm
Constipation
Urinary retention
Chest wall rigidity (may interfere with ventilation)

Cautions
Enhanced sedative and respiratory depression from interaction with:
• benzodiazepines
• antidepressants
• anti-psychotics
Avoid concomitant use of and for 2 weeks after MAOI discontinued (risk of CNS excitation or depression – hypertension, hyperpyrexia, convulsions and coma)
Head injury and neurosurgical patients (may exacerbate UP ICP as a result of UP PaCO2) Erythromycin (↓ clearance of alfentanil)

Organ failure:
Respiratory: UP respiratory depression Hepatic: enhanced and prolonged sedative effect