Pharmacokinetics and effects of 9-amino-1,2,3,4-tetrahydroacridine in the immediate postoperative period in neurosurgical patients.

STUDY OBJECTIVE

To determine the effects of intravenous (IV) 9-amino-1,2,3,4-tetrahydroacridine (THA) on postoperative somnolence in comparison to its pharmacokinetics.

DESIGN

Open-label study of the pharmacokinetics and effects of THA.

SETTING

Postoperative intensive care ward at the Department of Neurosurgery, Uppsala University Hospital, Sweden.

PATIENTS

Ten neurosurgical patients immediately after their operations were given 30 mg of THA for reversal of postoperative somnolence.

INTERVENTIONS

Plasma concentrations of THA and, in seven cases, the metabolite 1-hydroxy-THA were assayed using high-performance liquid chromatography. The pharmacokinetic data were compared to the degree of sedation and pain relief. After an IV dose of 30 mg THA, plasma concentrations were fit to an open two- or three-compartment model.

MEASUREMENTS AND MAIN RESULTS

The antagonistic effect of THA on sedation occurred immediately following IV administration and lasted 60 to 90 minutes. At a mean plasma THA concentration of 44 +/- 18 ng/ml, patients were resedated. There was no obvious relation between analgesia and plasma THA concentrations. Side effects such as nausea, salivation, and lower heart rate (HR) were observed in several patients. Plasma clearance (C1) was high and showed a twofold inter-individual variation, with a mean of 2.64 +/- 1.17 L/h. Volume of distribution (Vd gamma) varied between 300 and 850 liters, with a mean of 477 +/- 185 liters. The plasma half-lives of rapid and slow distribution, and elimination were 2.1 +/- 0.7 minutes, 26 +/- 18 minutes, and 133 +/- 48 minutes, respectively. Maximum plasma concentrations of 1-hydroxy-THA were 27 to 90 ng/ml in five patients; the concentration was below 1 ng/ml in two other patients.

CONCLUSIONS

The duration of the effects of THA as an antagonist of postoperative sedation was only about double that seen previously after the IV administration of physostigmine in a similar group of patients, although the elimination half-life of THA was six times longer than that of physostigmine. A larger dose of THA possibly could have been given to prolong the period of antagonism of sedation, but the profile of adverse effects seen even at the doses used precluded that option.