Alfentanil HCL (Alfenta)

By | 2013-06-08

Opiate Anesthetic Adjunct

Highlights Of Prescribing Information

Injectable, potent opiate that may be useful for adjunctive anesthesia, particularly in cats

Marginal veterinary experience & little published data available to draw conclusions on appropriate usage in veterinary species

Dose-related respiratory & CNS depression are the most likely adverse effects seen

Dose may need adjustment in geriatric patients & those with liver disease

Class-ll controlled substance; relatively expensive

What Is Alfentanil HCL Used For?

An opioid analgesic, alfentanil may be useful for anesthesia, analgesia, or sedation similar to fentanyl; fentanyl is generally preferred because of the additional experience with its use in veterinary patients and cost. Alfentanil may be particularly useful in cats as adjunctive therapy during anesthesia to reduce other anesthetic (i.e., propofol or isoflurane) concentrations.


Alfentanil is a potent mu opioid with the expected sedative, analgesic, and anesthetic properties. When comparing analgesic potencies after IM injection, 0.4-0.8 mg of alfentanil is equivalent to 0.1-0.2 mg of fentanyl and approximately 10 mg of morphine.


The pharmacokinetics of alfentanil have been studied in the dog. The drug’s steady state volume of distribution is about 0.56 L/kg, clearance is approximately 30 mL/kg/minute, and the terminal half-life is approximately 20 minutes.

In humans, onset of anesthetic action occurs within 2 minutes after intravenous dosing, and within 5 minutes of intramuscular injection. Peak effects occur approximately 15 minutes after IM injection. The drug has a volume of distribution of 0.4-1 L/kg. About 90% of the drug is bound to plasma proteins. Alfentanil is primarily metabolized in the liver to inactive metabolites that are excreted by the kidneys into the urine; only about 1% of the drug is excreted unchanged into the urine. Total body clearance in humans ranges from 1.6-17.6 mL/minute/kg. Clearance is decreased by about 50% in patients with alcoholic cirrhosis or in those that are obese. Clearance is reduced by approximately 30% in geriatric patients. Elimination half-life in humans is about 100 minutes.

Before you take Alfentanil HCL

Contraindications / Precautions / Warnings

Alfentanil is contraindicated in patients hypersensitive to opioids. Because of the drug’s potency and potential for significant adverse effects, it should only be used in situations where patient vital signs can be continuously monitored. Initial dosage reduction may be required in geriatric or debilitated patients, particularly those with diminished cardiopulmonary function.

Adverse Effects

Adverse effects are generally dose related and consistent with other opiate agonists. Respiratory depression, and CNS depression are most likely to be encountered. In humans, bradycardia that is usually responsive to anticholinergic agents can occur. Dose-related skeletal muscle rigidity is not uncommon and neuromuscular blockers are routinely used. Alfentanil has rarely been associated with asystole, hypercarbia and hypersensitivity reactions.

Respiratory or CNS depression maybe exacerbated if alfentanil is given with other drugs that can cause those effects.

Reproductive / Nursing Safety

In humans, the FDA categorizes alfentanil as a category C drug for use during pregnancy (Animal studies have shown an adverse effect on the fetus, hut there are no adequate studies in humans; or there are no animal reproduction studies and no adequate studies in humans). If alfentanil is administered systemically to the mother close to giving birth, offspring may show behavioral alterations (hypotonia, depression) associated with opioids. Although high dosages given for 10-30 days to laboratory animals have been associated with embryotoxicity, it is unclear if this is a result of direct effects of the drug or as a result of maternal toxicity secondary to reduced food and water intake.

The effects of alfentanil on lactation or its safety for nursing offspring is not well defined, but it is unlikely to cause significant effects when used during anesthetic procedures in the mother.

Overdosage / Acute Toxicity

Intravenous, severe overdosages may cause circulatory collapse, pulmonary edema, seizures, cardiac arrest and death. Less severe overdoses may cause CNS and respiratory depression, coma, hypotension, muscle flaccidity and miosis. Treatment is a combination of supportive therapy, as necessary, and the administration of an opiate antagonist such as naloxone. Although alfentanil has a relatively rapid half-life, multiple doses of naloxone may be necessary. Because of the drug’s potency, the use of a tuberculin syringe to measure dosages less than 1 mL with a dosage calculation and measurement double-check system, are recommended.

How to use Alfentanil HCL

(Note: in very obese patients, figure dosages based upon lean body weight.)

Alfentanil HCL dosage for dogs:

As a premed:

a) 5 mcg/kg alfentanil with 0.3-0.6 mg of atropine IV 30 seconds before injecting propofol can reduce the dose of propofol needed to induce anesthesia to 2 mg/kg, but apnea may still occur. ()

As an analgesic supplement to anesthesia:

a) 2-5 mcg/kg IV q20 minutes. ()

b) For intra-operative analgesia in patients with intracranial disease: 0.2 mcg/kg/minute ()


■ Anesthetic and/or analgesic efficacy

■ Cardiac and respiratory rate

■ Pulse oximetry or other methods to measure blood oxygenation when used for anesthesia

Client Information

■ Alfentanil is a potent opiate that should only be used by professionals in a setting where adequate patient monitoring is available

Chemistry / Synonyms

A phenylpiperidine opioid anesthetic-analgesic related to fentanyl, alfentanil HCL occurs as a white to almost white powder. It is freely soluble in alcohol, water, chloroform or methanol. The commercially available injection has a pH of 4-6 and contains sodium chloride for isotonicity. Alfentanil is more lipid soluble than morphine, but less so than fentanyl.

Alfentanil may also be known as: alfentanyl, Alfenta, Fanaxal, Fentalim, Limifen, or Rapifen.

Storage / Stability/Compatibility

Alfentanil injection should be stored protected from light at room temperature. In concentrations of up to 80 mcg/mL, alfentanil injection has been shown to be compatible with Normal Saline, D5 in Normal Saline, D5W, and Lactated Ringers.

Dosage Forms / Regulatory Status

Veterinary-Labeled Products: None

The ARCI (Racing Commissioners International) has designated this drug as a class 1 substance. See the appendix for more information.

Human-Labeled Products:

Alfentanil HCL for injection: 500 mcg/mL in 2 mL, 5 mL, 10 mL, and 20 mL amps; preservative free; Alfenta (Akorn); Alfentanil HCL (Abbott); (Rx, C-II).