Opiate receptors are coupled with G-protein receptors and function as both positive and negative regulators of synaptic transmission via G-proteins that activate effector proteins. Binding of the opiate stimulates the exchange of GTP for GDP on the G-protein complex. As the effector system is adenylate cyclase and cAMP located at the inner surface of the plasma membrane, opioids decrease intracellular cAMP by inhibiting adenylate cyclase. Subsequently, the release of nociceptive neurotransmitters such as substance P, GABA, dopamine, acetylcholine and noradrenaline is inhibited. Opioids also inhibit the release of vasopressin, somatostatin, insulin and glucagon. Alfentanil's analgesic activity is, most likely, due to its conversion to morphine. Opioids close N-type voltage-operated calcium channels (OP2-receptor agonist) and open calcium-dependent inwardly rectifying potassium channels (OP3 and OP1 receptor agonist). This results in hyperpolarization and reduced neuronal excitability.
Used for anesthesia in surgery. It is an analogue of fentanyl with around 1/4 to 1/10 the potency of fentanyl and around 1/3 of the duration of action, but with an onset of effects 4x faster than fentanyl. Alfentanil has a pKa of approximately 6.5, which leads to a very high proportion of the drug being uncharged at physiologic pH. This unique characteristic is responsible for its rapid onset. It is an agonist at mu opioid receptors.
The most common adverse reactions of opioids are respiratory depression and skeletal muscle rigidity, particularly of the truncal muscles. Alfentanil may produce muscular rigidity that involves the skeletal muscles of the neck and extremities. The management of respiratory depression and skeletal muscle rigidity.
The adverse experience profile from 696 patients receiving alfentanil for Monitored Anesthesia Care (MAC) is similar to the profile established with alfentanil during general anesthesia. Respiratory events reported during MAC included hypoxia, apnea, and bradypnea. Other adverse events reported by patients receiving alfentanil for MAC, in order of decreasing frequency, were nausea, hypotension, vomiting, pruritus, confusion, somnolence and agitation.
The following adverse reaction information is derived from controlled and open clinical trials in 785 patients who received intravenous alfentanil during induction and maintenance of general anesthesia. The controlled trials included treatment comparisons with fentanyl, thiopental sodium, enflurane, saline placebo and halothane. The incidence of certain side effects is influenced by the type of use, e.g., chest wall rigidity has a higher reported incidence in clinical trials of alfentanil induction, and by the type of surgery, e.g., nausea and vomiting have a higher reported incidence in patients undergoing gynecologic surgery. The overall reports of nausea and vomiting with alfentanil were comparable to fentanyl.
Incidence Greater than 1% - Probably Causally Related (Derived from clinical trials)
Gastrointestinal: nausea (28%), vomiting (18%)
Cardiovascular: arrhythmia, bradycardia (14%), hypertension (18%), hypotension (10%), tachycardia (12%)
Musculoskeletal: chest wall rigidity (17%), skeletal muscle movements*
Respiratory: apnea*, postoperative respiratory depression
Central Nervous System: blurred vision, dizziness*, sleepiness/postoperative sedation
*Incidence 3% to 9% All others 1% to 3%
Incidence Less than 1% - Probably Causally Related (Derived from clinical trials)
Adverse events reported in post-marketing surveillance, not seen in clinical trials, are italicized.
Body as a whole: anaphylaxis
Central Nervous System: headache*, myoclonic movements, postoperative confusion*, postoperative euphoria*, shivering*
Dermatological: itching*, urticaria*
Injection Site: pain*
Musculoskeletal: skeletal muscle rigidity of neck and extremities
Respiratory: bronchospasm, hypercarbia*, laryngospasm*
The dosage of Alfentanil HCl injection should be individualized and titrated to the desired effect in each patient according to body weight, physical status, underlying pathological condition, use of other drugs, and type and duration of surgical procedure and anesthesia. In obese patients (more than 20% above ideal total body weight), the dosage of Alfentanil HCl injection should be determined on the basis of lean body weight. The dose of Alfentanil HCl injection should be reduced in elderly or debilitated patients.
Both the magnitude and duration of central nervous system and cardiovascular effects may be enhanced when alfentanil is administered in combination with other CNS depressants such as barbiturates, tranquilizers, opioids, or inhalation general anesthetics. Postoperative respiratory depression may be enhanced or prolonged by these agents. In such cases of combined treatment, the dose of one or both agents should be reduced. Limited clinical experience indicates that requirements for volatile inhalation anesthetics are reduced by 30 to 50% for the first sixty (60) minutes following alfentanil induction.
The concomitant use of erythromycin with alfentanil can significantly inhibit alfentanil clearance and may increase the risk of prolonged or delayed respiratory depression.
Cimetidine reduces the clearance of alfentanil. Therefore smaller alfentanil doses will be required with prolonged administration and the duration of action of alfentanil may be extended.
Perioperative administration of drugs affecting hepatic blood flow or enzyme function may reduce plasma clearance and prolong recovery.
Alfentanil hydrochloride is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store alfentanil hydrochloride in the bathroom or the freezer. There may be different brands of alfentanil hydrochloride that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.
Before using this drug, tell your doctor if:
Obstructive airway disease or respiratory depression if not ventilating.
Concurrent administration with monoamine oxidase inhibitors or within 2 weeks of their discontinuation.
Administration in labor or before clamping of the cord during Caesarian section due to the possibility of respiratory depression in the new-born infant.
Delayed respiration depression, respiratory arrest, bradycardia, asystole, arrhythmias and hypotension have also been reported. Therefore, vital signs must be monitored continuously.