Alfentanil is synthetic opioid Phenylpiperidine series-Tetrazole derivative of fentanyl Introduced in 1980. Less potent(1/5th to 1/10th ) and Has 1/3rd the duration of action of fentanyl. It is Agonist at µ-receptor.
PHARMACODYNAMICS Central nervous system: Generalized slowing of the EEG. Intense muscle rigidity accompanied by loss of consciousness. No significant changes in ICP. Increases CSF pressure in patient with brain tumour(Jung R et al;Anaesth Analog 1990).
RESPIRATORY SYSTEM Decreases respiratory rate,Tidal volume and increases airway resistance Ventilatory response to CO2 is decreased by 50% of the baseline value. Higher doses may produce apnea and a longer duration of respiratory depression.
CARDIOVASCULAR SYSTEM: Blunt cardiovascular and catecholamine responses to laryngoscopy and intubation. MAP,SVR and Pulmonary capillary wedge pressure are unaffected. Bradycardia and hypotension occurs when combined with propofol(1mg/kg).
GASTROINTESTINAL SYSTEM Nausea and vomting. Decreases GI motility and secretions. Increases common bile duct pressure-spasm of Sphincter of Oddi.
PHARMACOKINETICS Less lipid soluble, weaker base than other opioid pKa 6.8(others>7.4) results in 90% unbound plasma alfenatanil being non ionized at 7.4. Distribution:85-92% protein bound,volume of distribution(0.4-1 L/kg)smaller than fentanyl(3-8L/kg).
Distribution half life:1 to 3.5 minutes. Elimination half life:84 to 90 minutes. Context-sensitive half life(time necessary for the plasma concentration to decrease 50% after discontinuation of the infusion):after 4 hours of infusion is 60 mins.
DOSAGE AND USES: Premedication: Dose: 250-500mcg. Induction with hypnotic: Dose:25-50mcg/kg IV
Maintenance of anaesthesia: Intermittent bolus dose:- 5-10mcg/kg. Infusion:- 0.5-2mcg/kg/min.Total dose: Dependent on duration of procedure
MONITORED ANESTHESIA CARE (MAC) (For sedated and responsive,spontaneously breathing patients). Induction of MAC: 3-8 mcg/kg Maintenance of MAC: 0.25 to 1 mcg/kg/min Total dose: 3-40 mcg/kg.
Anilidopiperidine derivative. Introduced in 1991. Analgesic potency similar to fentanyl. (20-30 times more potent than alfentanil) Ultra short acting
PHARMACODYNAMICS CNS: Concentration dependent slowing of EEG. Muscle rigidity-bolus doses. No effect on ICP. Preserves cerebral autoregulation. Less suppression of MEP compared to other opioids. Dose dependent decrease in CPP. No seizure activity.
CARDIOVASCULAR SYSTEM: Dose dependent decrease in MAP. Dose dependent hypotension and bradycardia
RESPIRATORY SYSTEM: Dose dependent respiratory depression. Ventilatory response to CO2 is decreases by 50% of the baseline value. Recovery from remifentanil-induced respiratory depression is rapid-minute ventilation returns to baseline by 5-10 mins after the infusion s stopped.
GASTROINTESTINAL SYSTEM: Nausea(44%) and vomiting(21%). Delays gastric emptying and biliary drainage
PHARMACOKINETICS: Smaller volume of distribution Vd-100ml/kg. Rapid clearance-40ml/min/kg. Metabolised by non specific plasma and tissue esterases to inactive metabolites. Clearance is not affected by Cholinesterase deficiency or anticholinergics.
Distribution half life:1 minute Elimination half life:3-10 minutes. Context-sensitive half life:4 minutes-independent of the duration of infusion.
DOSAGE AND USES:1)Induction: Dose:0.5-1mcg/kg IV over 60 to 90 seconds.2)Maintenance of anaesthesia: -N2O(66%)+Isoflurane(0.4-1.5MAC) Dose:0.05-0.2mcg/kg/min. -Propofol(100-200mcg/kg/min) Dose:- 0.05-0.2mcg/kg/min
3)Maintenance of anaesthesia in pediatric patients: -Birth to 2mnths of age N2o(70%):- 0.4-1mcg/kg/min. -1 to 12 yrs of age halothane/sevoflurane/isoflurane dose:-0.05-1.3mcg/kg/min.
4) Monitored Anesthesia Care: -Single dose: 0.5-1mcg/kg over 30 to 60 seconds,give 90 seconds before the local anaesthetics. -Conti.infusion:Begining 5mins before local anaesthetics 0.1mcg/kg/min. after local anaesthetics 0.05mcg/kg/min.
REFERENCES:1)Clinical Anesthesia 6th edn,Paul G.Barash.2)Pharmacology and Physiology in Anesthetic Practice 4th edn,Robert K. Stoelting.3)Miller’s Anesthesia 7th edn.4)Internet references.