Intratracheal administration of fentanyl: pharmacokinetics and local tissue effects

To study the pharmacokinetics and local tissue effects resulting from the intratracheal administration of preservative-free fentanyl.

Prospective, randomized, blinded and controlled animal study.

University research laboratory.

Eighteen adult male New Zealand rabbits.

Preservative-free fentanyl citrate or normal saline was administered by the intratracheal (i.t.) and intravenous (i.v.) routes to randomized groups of rabbits. The animals were killed at 24, 48 and 72 h following administration.

Plasma concentrations of fentanyl were measured before administration and at 2, 5, 10, 30, 60 and 120 min following administration by a specific radioimmunoassay. A detailed histological examination of the lung and tracheal tissue was performed to identify local side effects. There were no significant differences in the plasma fentanyl concentrations resulting from the i.v. or i.t. route of administration. In both groups, the concentrations of fentanyl were within the therapeutic range (i.t. 2.37 ng/ml, i.v. 2.53 ng/ml) by 2 min after injection and reached a maximum concentration within 5 min. The bioavailability of i.t. fentanyl was 71%. Microscopic examination of the respiratory system did not show significant differences between the two random groups overall. However, in the sub-group of animals killed at 24 h, more animals in the i.t. group showed signs of inflammation in the lung parenchyma.

There is rapid absorption of fentanyl following i.t. administration. Pharmacokinetic parameters for fentanyl were not significantly altered by the route of administration. Although there were no signs that i.t. administration of preservative-free fentanyl produces lung injury, a transient and mild inflammatory response was detected at 24 h after administration.