Liquid chromatography of amitriptyline and related tricyclic compounds

Development of a rapid extraction and high-performance liquid chromatographic separation for amitriptyline and six biological metabolites

The development of a rapid high-performance liquid chromatographic method for the determination of amitriptyline, amitriptyline-N-oxide, 10-hydroxyamitriptyline, 10-hydroxynortriptyline (E and Z isomers), nortriptyline and desmethylnortriptyline in plasma and liver tissue is described. A liquid--liquid extraction with hexane--butanol and back-extraction into phosphoric acid provides efficient extraction of amitriptyline-N-oxide along with amitriptyline and the other metabolites. A Supelcosil C8 reversed-phase column with 5-micron packing and a methanol--sodium phosphate buffer--amine modifier mobile phase was used. The combination of mobile phase pH and amine modifier concentration for the best separation within a reasonable analysis time for all seven solutes plus an internal standard was determined using a factorial design coupled with a multi-factor window diagram technique. Ultraviolet detection at 214 nm provided limits of detection of approximately 1 ng/ml.

Amitriptyline and oxaprotiline in the treatment of hospitalized depressive patients. Clinical aspects, psychophysiology, and drug plasma levels

Amitriptyline (AT) and the noradrenaline reuptake inhibiting antidepressant oxaprotiline (OT = hydroxymaprotiline) were compared in 59 primary depressive inpatients in a 4-week double blind parallel group design. In the Hamilton Depression Rating Scale and 2 self-rating scales AT proved to be more efficient than OT, mainly with respect to disturbances of appetite and sleep. Agitated patients receiving OT needed more additional tranquilizing medication. The number of side-effects did not differ. Both drugs increased heart rate and skin resistance level (SRL) to about the same degree and did not influence the number of spontaneous fluctuations of SRL, habituation of SRL orienting responses (OR), frequencies of respiration and blinking. Salivation was temporarily more impaired by AT. All physiological variables differed between patients and 30 healthy controls during the whole 4-week trial. Clinical outcome showed a linear relation to OT plasma levels. For AT a therapeutic window was confirmed for concentrations of AT and its metabolite nortriptyline between 125 and 200 ng/ml. Patients whose SRL-OR habituated rapidly had a better outcome than slow habituators. Urinary excretion of 3-methoxy-4-hydroxyphenylglycol was lower in patients than in controls but could not predict outcome with either drug.

Analysis of tricyclic antidepressant drugs in plasma and serum by chromatographic techniques

A review of methods for the determination of tricyclic antidepressants in plasma or serum, based on the application of chromatographic techniques, is presented. A general discussion of the techniques in terms of their precision, accuracy, sensitivity and selectivity, with respect to parent drug and metabolites, is used to facilitate a comparison of methods. No one technique can be claimed as the method of choice for these drugs, although gas-liquid chromatography with nitrogen selective detection has some strong claims, viz. generally good sensitivity and reproducibility of assays and ready availability of equipment in most laboratories. The ultimate choice of a method for determining tricyclics will be determined more by the clinical application (routine monitoring versus pharmacokinetics) than by other factors.

Solvent extraction of tricyclic amines from blood plasma and liquid chromatographic determination

The extraction of seven tricyclic antidepressant amines from human plasma at different pH values was investigated for dichloromethane, diethyl ether and hexane--1-pentanol (95:5). The amines were extracted as bases and back-extracted to sulphuric acid, 0.10 mol/l, prior to the separation by bonded-phase liquid chromatography. Ether and hexane--1-pentanol (95:5) were most suitable, tertiary amines being best extracted at pH 8, and secondary amines at pH 10. Using ether, both while 15 min ws sufficient for hexane--1-pentanol (95:5). UV detection allowed concentrations down to 10 ng in 1 ml of plasma to be determined. Three ammonium ions--octylammonium, dimethylammonium, and trimethylammonium--were added as modifiers to the mobile phase containing acetonitrile in phosphoric acid, 0.10 mol/l. In the concentration interval 0.010--0.030 mol/l all of the amine modifiers gave on Polygosil C8 peak asymmetry factors of sufficiently low magnitude, while on Li-Chrosorb RP-18 this was so only for di- and trimethylammonium in a concentration of 0.030 mol/l.

Antidepressants alter cerebrovascular permeability and metabolic rate in primates

External detection of the annihilation radiation produced by water labeled with oxygen-15 was used to measure cerebrovascular permeability and cerebral blood flow in six rhesus monkeys. Use of oxygen-15 also permitted assessment of cerebral metabolic rate in two of the monkeys. Amitriptyline produced a dose-dependent, reversible increase in permeability at plasma drug concentrations which are therapeutic for depressed patients. At the same concentrations the drug also produced a 20 to 30 percent reduction in cerebral metabolic rate. At higher doses normal autoregulation of cerebral blood flow was suspended, but responsivity to arterial carbon dioxide was normal.

Simultaneous determination of amitriptyline, nortriptyline and their respective isomeric 10-hydroxy metabolites in plasma by liquid chromatography

An ion-pair reversed-phase liquid chromatographic method for the determination of the tricyclic antidepressant amitriptyline, the demethylated metabolite nortriptyline, and their respective cis- and trans-hydroxylated metabolites in plasma is presented. After extraction from 1 ml of plasma, the reconstituted residue was chromatographed on a trimethylsilyl packed column using a mobile phase of acetonitrile and acetate buffer with sodium heptane-sulfonate and triethylamine. Recovery of the drugs and its metabolites from plasma ranged from 56 to 99%. The method is suitable for determining plasma concentrations as low as 5 ng/ml (C.V. less than 9%) for all six compounds. Plasma concentrations of amitriptyline and its metabolites from eleven different patients are presented.

A liquid chromatographic method for quantitating amitriptyline in brain tissue

A previously reported method for measuring tricyclic antidepressants (TCA) in plasma was modified to measure TCA, specifically amitriptyline (AMI) and nortriptyline (NOR) in rat brain tissue. Brains obtained from drug-free and AMI-treated rats were extracted and assayed using a Waters high-performance liquid chromatograph. Drug-free brain tissue contained no substances which interfered with the assay of these TCAs. Drug recovery averaged 90 +/- 3.4% (mean +/- SEM). Seven intra-run assays of a spiked brain tissue sample yielded coefficients of variation of 2.7% for AMI and 1.8% for NOR. Seven inter-run assays of the same sample varied 4.2% for AMI and 3.5% for NOR. Five separate assays of a brain homogenate sample spiked with 50 ng/ml of drug yielded values of 50 +/- 2.1 SEM ng/ml for AMI and 54 +/- 1.1 SEM ng/ml for NOR. Standard curves were linear when constructed from samples in a concentration range of 250--3,000 ng/g wet weight tissue (r = 0.96, P less than 0.001).