Alfentanil

Comparative studies

Alfentanil has been compared with morphine in the attenuation of experimental muscle pain in 28 healthy volunteers [ ]. The two opioids had similar analgesic effects, with limited effects in attenuating central hypersensitivity, showing that other drugs (in combination or alone) would be required for adequate muscle pain with a central component. The two drugs had similar adverse effects profiles, the main effects being dizziness, tiredness, itching, and flushing. Nausea was more common after morphine. No volunteers withdrew because of adverse effects.

Alfentanil has been compared with fentanyl and remifentanil in 135 patients undergoing stereotactic brain biopsy [ ]. All regimens (intravenous alfentanil 7.5 micrograms/kg followed by 0.25 micrograms/kg/minute; intravenous fentanyl bolus 1 microgram/kg; and remifentanil 0.05 micrograms/kg/minute) provided similar hemodynamic and respiratory effects; however, fentanyl produced a lower mean heart rate, providing less hemodynamic stability.

Cardiovascular

When alfentanil 30 micrograms/kg was given to six healthy volunteers there were no clinical changes in respiratory or cardiovascular function [ ].

Bradycardia often occurs with the combination of a potent short-acting opioid with suxamethonium during induction of anesthesia, and alfentanil has been reported to have caused sinus arrest in three patients [ , ].

In one study alfentanil was particularly likely to cause hemodynamic instability and myocardial ischemia; however, drug interactions or the dosage regimen may have been responsible [ ].

Respiratory

Significant respiratory depression occurs after alfentanil in doses in excess of 1000 μg and delayed-onset respiratory depression has been reported. Used as a general anesthetic for urgent cesarean section, alfentanil can cause marked neonatal respiratory depression, which is reversible with naloxone [ ].

• A 35-year-old man developed recurrent respiratory depression after being given alfentanil 0.0125 mg/kg for vitreoretinal surgery [ ]. General anesthesia was induced with a combination of propofol, rocuronium, and alfentanil, subsequent inhalation of isoflurane, and three additional doses of alfentanil (total 0.04 mg/kg over 2 hours). The pulse oxygen saturation fluctuated and was as low as 89% 180 minutes after extubation.

The severity of respiratory depression with alfentanil has been assessed in 49 patients undergoing abdominal hysterectomy under general anesthetic, who were randomly allocated to three groups [ ]. Group 1 did not receive alfentanil during surgery, group 2 received alfentanil 30 micrograms/kg, and group 3 received a bolus dose of alfentanil 10–20 micrograms/kg and an alfentanil infusion increasing in increments of 0.25–0.5 mg/kg/minute. In this randomized double-blind study alfentanil had respiratory depressant effects (measured by plethysmography and pulse oximetry), in one patient in group 1 and three each in groups 2 and 3, but there were no cases of clear-cut recurrent respiratory depression.

Alfentanil (20 micrograms/kg) and propofol (2 mg/kg) have been compared with propofol (2 mg/kg) and ketamine (1 mg/kg) in a prospective crossover study in 20 patients aged 2–15 years undergoing lumbar puncture [ ]. When alfentanil was used there was oxygen desaturation in 11, and nine required supplementary oxygen, compared with three when ketamine was used.

Nervous system

Increased intracranial pressure in normal pressure hydrocephalus patients has been described [ ]. An acute dystonic reaction has been reported in an untreated patient with Parkinson’s disease [ ].

Simultaneous scalp and depth electrode recordings were performed on five patients with complex partial epilepsy who underwent alfentanil anesthesia induction before depth electrode removal [ ]. Five equal bolus doses of alfentanil 100 μg were given to each patient at 60-second intervals (total dose 500 μg). Epileptiform activity was increased in three of the five, but without clinical evidence of seizure activity.

Gastrointestinal

Alfentanil is associated with a high incidence of nausea and vomiting. Droperidol can reduce emetic symptoms but metoclopramide does not [ , ].

• A 30-year-old woman with multiple body injuries required five general anesthetics in under 7 days for reconstructive surgery and dressing changes. In order to avoid further general anesthesia she was given a target-controlled infusion of alfentanil in 50 ml of 0.9% sodium chloride (a total dose of 5 mg over 35 minutes). There was one self-limiting episode of nausea with no vomiting. Oxygen saturation was 93–98% on air. There were no episodes of hypotension, cardiac dysrhythmias, or sedation [ ].

Musculoskeletal

Muscular rigidity involving many muscle groups has been described with alfentanil [ ].