Alfentanil

VerwendenThe low pKa of alfentanil (6.9) results in it being largely unionised at plasma pH, allowing rapid diffusion to the effect site (t1.2keo ~1min) and rapid onset of action despite it being less lipid soluble than other opioids. It does not bind strongly to opioid receptors, and the effect-site concentration also decreases rapidly as plasma concentrations decrease. Alfentanil is metabolised by the hepatic cytochrome P450 isoform CYP3A4. Genetic variability in the activity of this enzyme may result in two- to threefold variations in pharmacokinetic values when given by infusion. Low, medium or high metabolisers have been identified; this has implications for duration of action when prolonged use is contemplated.