Very large doses and multiple doses prolonged respiratory depression and delayed recovery could occur.
useful as a sedative / analgesic premedication : 25 to 50 µg IV.
A transmucosal delivery system is effective premedicant for pediatric and adult patients as well as an effective treatment for “breakthrough” pain in chronic pain patients, should be administered in a monitored environment .
Severe hypotension has been observed when alfentanil is given after 0.125 mg / kg diazepam .
Alfentanil can also cause bradycardia.
Minimized by premedication with atropine and by the vagolytic effect of pancuronium .
Alfentanil 50 µg/kg combined with propofol 1 mg/kg for induction of anesthesia can produce significant bradycardia and hypotension after intubation, but premedication with glycopyrrolate prevents these effects.
Remifentanil is an ester functional group that hydrolyzed by blood and tissue nonspecific esterases and results in very rapid metabolism .
Because butyrocholinesterase ( pseudocholinesterase ) does not appear to metabolize remifentanil, plasma cholinesterase deficiency and anticholinergic administration do not affect remifentanil clearance .
Unlike other opioids, redistribution plays only a minor role in remifentanil clearance .
The most commonly reported remifentanil - based regimen for anesthetic induction and laryngoscopy consists of remifentanil 0.5 to 1 µg / kg given over 60 seconds plus propofol 1 to 2 mg / kg , followed by remifentanil infusion of 0.25 to 0.5 µg / kg / min .
Patients who received low - dose ( 12.5 to 25 µg ) intermittent bolus injection of remifentanil with or without infusion at 0.05 µg / kg / min reported better analgesia than continuous infusion of 0.1 µg / kg / min alone .
The observed effect of the combination of A and B is expressed as a fraction of the maximal effect of the full agonist . As the concentration of the partial agonist increases, the effect of the combination converges on the maximum effect of the partial agonist . When added to a low concentration ( e . g . , [ A ] = 0.25 ) of agonist, the partial agonist increases the response; but when added to a large concentration of the agonist, the response decreases—that is, B acts like an antagonist .
Nalbuphine and butorphanol have been reported to be antagonists at the µ opioid receptor, they do cause respiratory depression, which is not a function of κ agonists . Thus, they appear to have at least partial agonist activity at the µ - opioid receptor .
During an infusion, the peripheral ( fast and slow ) compartments begin to “fill up . ” After the infusion is stopped, drug will be eliminated, but will also continue to be redistributed as long as the concentration in a peripheral compartment is lower than that in the central compartment . This leads to a rapid drop in central compartment drug concentration .
When central compartment ( plasma ) concentration drops below that of the peripheral compartment ( s ) , the direction of drug redistribution will reverse and will slow the decline in plasma concentration .
The degree to which redistribution will affect the rate of drug elimination depends on the ratio of the distributional to elimination time constants . Thus, a drug that can rapidly redistribute will have a correspondingly larger contribution from the peripheral compartment ( s ) , and plasma concentration will drop progressively more slowly as infusion duration continues .