Alfentanil
OVERVIEW
- Alfentanil is a potent synthetic mu-opioid receptor agonist analgesic drug
- It is a analogue of the synthetic opioid fentanyl that is only 10% as potent (on a weight-to-weight basis), but has quicker onset, quicker time to maximal effect, shorter duration of action (10 minutes), is more cardiovascularly stable and has more respiratory depression
PREPARATION
- Ampoules: 1 mg / 2 mL or 5 mg/10 mL
DOSES
Bolus IV sedation:
- The usual single IV bolus dose is around 5 -7 micrograms/ kg (e.g. 350 – 700 micrograms for a 70kg adult)
- further 2- 3micrograms/ kg doses q10-15min prn
- Higher doses may be given to mechanically ventilated patients with airway protection
Anaesthetic induction
- 10 – 50 mcg/ kg IV
MECHANISM OF ACTION
- Alfentanil binds opioid receptors, and is most active at the mu receptors.
- Effects are analesia, sedation, anxiolysis and induction of anaesthesia
PHARMACOKINETICS
- Absorption – IV bolus or infusion with maximal effect in 1-2 minutes
- Distribution – Vd varies from 0.4 to 1.0 L/kg (10% of that of fentanyl) due to limited liposolubility and extensive plasma protein binding (mainly to alpha1-acid glycoprotein)
- Metabolism – extensive liver metabolism
- Elimination – only 1% excreted in the liver in active form
INDICATIONS
- Adjunctive analgesia during anaesthetics for short duration procedures or longer duration proceudres (e.g. used as an infusion)
- Stand alone sedation for short painful procedures in the Emergency Department
CONTRA-INDICATIONS/ PRECAUTIONS
- Respiratory disease e.g. Severe obstructive airways disease, those at risk of upper airways obstruction, obstructive sleep apnea
- Depressed conscious state or concomitant CNS depressant use
- Hypotension
- Hepatic impairment (risk of excessive sedation)
- elderly (use lower doses)
- infants <12 months ( more susceptible to respiratory depression, use lower doses)
- allergy
- pregnancy (fentanyl is category C)
ADVERSE EFFECTS (typical of opioids)
- CNS
- decreased conscious state, with attendant risk of airway compromise (may cause death)
- Euphoria, dysphoria, delirium, hallucinations
- lowers seizure threshold
- RESP (increased with alfentanil cf fentanyl)
- Respiratory depression or arrest (may cause death; synergistic with other respiratory depressants)
- GI
- Nausea and vomiting (due to stimulation of the chemoreceptor trigger zone – consider prophylactic antiemetics)
- decreased GI motility with delay in gastric emptying and constipation
- CVS (decreased with alfentanil cf fentanyl)
- Hypotension, bradycardia (especially with large or rapid IV boluses)
- allergic reactions (uncommon), direct histamine release is rare for synthetic opioids such as alfentanil
- urinary retention (increased bladder sphincter tone)
- dependence, addiction, withdrawal, tolerance
ANTIDOTE
- Naloxone
References and Links
CCC Pharmacology Series
Respiratory: Bosentan, Delivery of B2 Agonists in Intubated Patients, Nitric Oxide, Oxygen, Prostacyclin, Sildenafil
Cardiovascular: Adenosine, Adrenaline (Epinephrine), Amiodarone, Classification of Vasoactive drugs, Clevidipine, Digoxin, Dobutamine, Dopamine, Levosimendan, Levosimendan vs Dobutamine, Milrinone, Noradrenaline, Phenylephrine, Sodium Nitroprusside (SNiP), Sotalol, Vasopressin
Neurological: Dexmedetomidine, Ketamine, Levetiracetam, Lignocaine, Lithium, Midazolam, Physostigmine, Propofol, Sodium Valproate, Sugammadex, Thiopentone
Endocrine: Desmopressin, Glucagon Therapy, Medications and Thyroid Function
Gastrointestinal: Octreotide, Omeprazole, Ranitidine, Sucralfate, Terlipressin
Genitourinary: Furosemide, Mannitol, Spironolactone
Haematological: Activated Protein C, Alteplase, Aprotinin, Aspirin, Clopidogrel, Dipyridamole, DOACs, Factor VIIa, Heparin, LMW Heparin, Protamine, Prothrombinex, Tenecteplase, Tirofiban, Tranexamic Acid (TXA), Warfarin
Antimicrobial: Antimicrobial Dosing and Kill Characteristics, Benzylpenicillin, Ceftriaxone, Ciprofloxacin, Co-trimoxazole / Bactrim, Fluconazole, Gentamicin, Imipenem, Linezolid, Meropenem, Piperacillin-Tazobactam, Rifampicin, Vancomycin
Analgesic: Alfentanil, Celecoxib, COX II Inhibitors, Ketamine, Lignocaine, Morphine, NSAIDs, Opioids, Paracetamol (Acetaminophen), Paracetamol in Critical Illness, Tramadol
Miscellaneous: Activated Charcoal, Adverse Drug Reactions, Alkali Therapies, Drug Absorption in Critical Illness, Drug Infusion Doses, Epidural Complications, Epidural vs Opioids in Rib Fractures, Magnesium, Methylene Blue, Pharmacology and Critical Illness, PK and Obesity, PK and ECMO, Sodium Bicarbonate Use, Statins in Critical Illness, Therapeutic Drug Monitoring, Weights in Pharmacology
Toxicology: Digibind, Flumazenil, Glucagon Therapy, Intralipid, N-Acetylcysteine, Naloxone, Propofol Infusion Syndrome
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
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