Determination of amitriptyline and some of its metabolites in blood by high-pressure liquid chromatography

High-performance liquid chromatographic determination of amitriptyline and its main metabolites using a silica column with reversed-phase eluent. Application in mice

A method was developed for the assay of amitriptyline, amitriptyline N-oxide, nortriptyline, desmethylnortriptyline and E (trans) and Z (cis) isomers of 10-hydroxyamitriptyline and of 10-hydroxynortriptyline in plasma and brain of animals, using high-performance liquid chromatography with ultraviolet detection (254 nm). Single extraction was performed at pH 10.5 from 0.25 ml of plasma or 1 ml of brain mixture. Chromatographic separations were achieved with a silica column and an aqueous methanol mobile phase containing ammonia. This procedure offers high sensitivity (8-10 ng/ml), high linearity (r > 0.99) and acceptable precision (coefficient of variation < or = 13.3%). The method was used to determine levels of amitriptyline and its major metabolites in mice 30 min after a single intraperitoneal administration of amitriptyline (20 mg/kg).

Retention characteristics in high-performance liquid chromatography of basic drugs and plasma extracts on an alumina column

The retention characteristics of 35 drugs on an alumina column using buffered aqueous methanolic mobile phases have been investigated. It has been shown that the effect of pH on retention depends on the pKa of the drug and the type of buffer ion used; that there is an inverse relation between ionic strength and solute retention; and that a decrease in the amount of methanol in the mobile phase causes the drugs to be held longer on the column. The chromatographic system was also coupled to an on-line column-switching assembly to facilitate extraction of the drugs from plasma, and results are presented which indicate that the alumina column lends itself well to this convenient method of plasma clean-up.

Two tricyclic antidepressant poisonings: levels of amitriptyline, nortriptyline and desipramine in post-mortem biological samples

Two deaths due to amitriptyline and desipramine overdoses are reported. The first case deals with a 20-year-old Caucasian male who was found dead at his residence. Toxicological analysis of the blood, urine, liver and kidney revealed the presence of amitriptyline (1.7 mg/l, 0.13 mg/l, 36.0 mg/kg and 98.0 mg/kg) and nortriptyline (0.66 mg/l, 0.74 mg/l, 12.0 mg/kg and 37.0 mg/kg). The gastric content contained only 220 mg of amitriptyline. The urine also contained norverapamil, which was consistent with previous verapamil therapy. The second case involved a 19-year-old Caucasian male who attempted suicide earlier and was on desipramine medication. The blood, urine, liver and gastric content disclosed the presence of desipramine in the concentrations of 14.2 mg/l, 33.7 mg/l, 112.5 mg/kg and 180 mg, respectively. The levels of these tricyclics analyzed by high pressure liquid chromatography were in agreement with the levels reported in the literature. Though with the amitriptyline poisoning no significant anatomic changes were noted, the desipramine-caused death was further supported by the multisystem vascular congestion and ischemic changes consistent with cardiopulmonary failure.

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.

Profiling of impurities in illicit amphetamine samples by high-performance liquid chromatography using column switching

A simple high-performance liquid chromatographic method, suitable for routine profiling of impurities in illegally produced amphetamine, has been developed. Amphetamine is dissolved in acetonitrile-citrate buffer (pH 3) (2:8) and injected directly without further sample pre-treatment. The impurities are enriched on-line on a C8 extraction column, while amphetamine and polar diluents are washed out with water. After washing for 1.5 min, a six-port valve is switched and an acetonitrile-0.2 M butylamine in water (pH 8) gradient elutes the impurities from the extraction column on to a C18 analytical column where they are separated. The compounds are monitored by UV detection at 220 and 254 nm. The total extraction and analysis time is 30 min. The method allows automated extraction and analysis to be performed.

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.

Gas chromatographic--mass spectrometric determination of amitriptyline and its major metabolites in human serum

A gas chromatographic--electron-impact ionization mass spectrometric method has been developed for the determination of amitriptyline (AMT) and its metabolites, nortriptyline (NT), 10-hydroxyamitriptyline (10-OH-AMT) and 10-hydroxynortriptyline (10-OH-NT) in human serum. The lower limit of detection was 2 ng/ml for all compounds except 5 ng/ml for 10-OH-NT. The calibration curves for AMT and 10-OH-AMT were linear up to 100 ng/ml, and up to 200 ng/ml for NT and 10-OH-NT. The accuracy of the assay in terms of coefficient of variation was less than 7%. The extraction efficiency was almost quantitative for all compounds except 60% for 10-OH-NT. Using this method, human serum samples which had been collected after oral administration of a single 50-mg dose of AMT were analyzed. Ratios of the conjugation of each metabolite were estimated, including AMT.

The analysis of tricyclic antidepressant drugs at therapeutic blood levels by reversed-phase high-performance liquid chromatography using pairing and organic counter-ions

A serum assay method incorporating two internal standards suitable for routine clinical analysis of tricyclic antidepressant drugs at the therapeutic level is described. The method involves extraction and chromatography using a reversed-phase high-performance liquid chromatography system incorporating pairing and organic counter-ions. The quantitative characteristics of the method are reported and results are compared with consensus values for four commonly encountered drugs, amitriptyline, nortriptyline, imipramine and desipramine. The method is shown to be applicable to more recently developed antidepressants such as nomifensine and maprotiline and the flexibility of the chromatography is discussed. Sample chromatograms obtained from patient samples in the presence and absence of potentially interfering drugs and metabolites are discussed.

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.

Determination of cyclobenzaprine in tablets by high-performance liquid chromatography

A convenient high-performance liquid chromatographic method for the quantitative determination of cyclobenzaprine hydrochloride in tablets is described. Samples were dissolved in 0.05 N sulfuric acid and diluted with methanol. The cyclobenzaprine hydrochloride was chromatographed using an octylsilane column and the eluent acetonitrile-0.6% dibasic potassium phosphate aqueous buffer (pH 3.0) (75:25) at a flow rate of 1.5 ml/min. Naphazoline hydrochloride was used as an internal standard. The UV detector response at 254 nm was linear for cyclobenzaprine hydrochloride in the 0.005-0.03 mg/ml range under conditions of the analysis.

Reversed-phase liquid chromatography for the separation of chloropromazine, imipramine and some of their metabolites

Reversed-phase liquid chromatography on a C18 bonded silica with water-alcohol mixtures containing decylamine as the mobile phase was investigated for its applicability to the separation of chlorpromazine, imipramine and their metabolites. The addition of decylamine to the mobile phase was found to be necessary in order to obtain symmetrical peaks. The influence of the decylamine and ethanol concentrations and of the pH of the mobile phase was investigated and these parameters were found to be useful for the adjustment of the retention. The phase system developed was found to be suitable for the required separation. The phase system was applied to the analysis of imipramine and its metabolites, desmethylimipramine and didesmethylimipramine, and desmethylchlorpromazine in human plasma.

Determination of amitriptyline-N-oxide, amitriptyline and nortriptyline in serum and plasma by high-performance liquid chromatography

A method for the determination of amitriptyline-N-oxide, amitriptyline and nortriptyline in serum and plasma has been developed. After extraction from serum or plasma the drugs were analysed by high-performance liquid chromatography. The detection limit was 10 ng/ml (2 ml serum or plasma actually used). The coefficient of variation for all three compounds was below 10%. Amitriptyline-N-oxide was found in rat plasma after an oral dose (10 mg/kg) of amitriptyline-N-oxide.

Neuropharmacological properties of amitriptyline, nortriptyline and their metabolites

Amitriptyline, nortriptyline and their metabolites, desmethylnortriptyline, cis and trans 10-hydroxyamitriptyline, cis and trans 10-hydroxynortriptyline and amitriptyline-N-oxide, have been tested for inhibitory effect on the uptake of serotonin (rabbit thrombocytes in vitro) and noradrenaline (mouse atria in vitro and mouse heart in vivo), for anticholinergic activity (guinea-pig ileum in vitro) and for antagonism against tetrabenazine induced inactivity as well as apomorphine and 5-hydroxytryptophan potentiating effect in mice. Amitriptyline inhibits serotonin and noradrenaline uptake equally, whereas nortriptyline is a more potent inhibitor of noradrenaline than of serotonin uptake. The metabolites resemble nortriptyline in this respect. The 10-hydroxylated metabolites are equipotent with amitriptyline as regards noradrenaline uptake inhibition. All the metabolites are less anticholinergic than amitriptyline and nortriptyline. The in vitro results are reflected in the in vivo behavioural tests, although some discrepancies are found, probably due to differences in absorption, distribution, metabolism and excretion. The importance of knowledge concerning pharmacological properties of the metabolites in comparison with amitriptyline and nortriptyline for correlating plasma levels of these and their metabolites to clinical outcome is discussed.

Dynamic cation-exchange systems for the separation of drugs derived from butyrophenone and diphenylpiperidine by high-performance liquid chromatography and applied in the determination of halopemide in plasma

Dynamic (solvent generated) cation-exchange systems for the separation of drugs and main metabolites derived from butyrophenone and diphenylpiperidine (haloperidol, pimozide, halopemide) were investigated. The effect of organic modifier, detergent, counter-ion concentration and of the pH on the retention has been determined. The results show that variation of these parameters permits adjustment of the retention of these drugs over a wide range. The dynamic cation-exchange system developed was applied to the determination of halopemide and its main metabolite in plasma. The precision and detection limit of the method and the extraction efficiency were established. The time course of halopemide and plasma levels of patients chronically receiving halopemide are reported.

High-performance liquid chromatographic assay for imipramine, desipramine, and their 2-hydroxylated metabolites

High-performance liquid chromatographic method is presented for the simultaneous determination of imipramine, desipramine, and their 2-hydroxylated metabolites in plasma. The method involves a simple plasma extraction at basic pH with organic solvent, chromatography on a silica gel column, and fluorescence detection. Correlation with a GLC-mass spectrometric method for imipramine and desipramine is illustrated. The method can detect 1 ng of each component/ml of plasma, sufficient sensitivity for pharmocokinetic studies.

Reliable routine method for the determination of plasma amitriptyline and nortriptyline by gas chromatography

A gas chromatographic method has been developed for the determination of amitriptyline and nortriptyline in plasma. OV-17 is used in a 1 m long packed column, with a flame ionization detector and an electronic integrator. Five internal standards are added. The base-specific extraction procedure and the method of calibrating the chromatograph are described in detail. The accuracy, precision and reliability of the method are demonstrated by the results of nearly 700 determinations of each drug, at concentrations ranging from 5 to 400 ng/ml in the plasma. An interlaboratory comparison with a double radioactive isotope derivative assay for nortriptyline has also shown satisfactory agreement.

Separation of geometric isomers of retinyl ester, retinal and retinol, pertaining to the visual cycle, by high-performance liquid chromatography

A method for the analytical and/or preparative separation of the 13-cis, 11-cis, 9-cis and all all-trans isomers of retinyl palmitate ester, retinal and retinol by high-performance liquid chromatography is described. A straight-phase adsorption system consisting of Si 60 silica gel as the stationary phase and mixtures of n-hexane and dioxane as mobile phases were employed, using photometric detection at either 320 or 360 nm, depending on the nature of the compounds being studied. With simple adaptation of the phase system, all geometric isomers within each group could be separated. The precision of the method was 0.5% at the 10-microgram (about 40-nmole) level and 4% at the 10-ng (about 40-pmole) level (n = 3). The detection limit was about 0.5 ng (about 2 pmole). The suitability of the phase system is demonstrated by chromatograms of test mixtures and of eye extracts. The fractionation of 0.5 mg of an isomeric sample could be achieved on a column of length 250 mm and I.D. 10 mm.

Ion-pair liquid chromatography of amitriptyline and metabolites in plasma

A method is described for the determination of amitriptyline and nortriptyline in the plasma of patients during treatment. The method is based on liquid chromatography of the amines as ion-pairs with perchlorate. The separation column is packed with silica gel, and a mixture of diisopropyl ether, dichloromethane, methanol and water containing the counter ion is used as eluent. High efficacy and stability of the system is achieved. The separation of metabolites is demonstrated. The cis- and trans-10-hydroxy isomers of amitriptyline and nortriptyline are easily resolved with this chromatographic system.

Determination of the metabolites of bezitramide in urine. II. The basic metabolite

A high-performance liquid chromatographic method for the determination of low levels (less than 1 microgram/ml) of the basic metabolite of bezitramide, 1-(4-piperidinyl)-1,3-dihydro-2H-benzimidazol-2-one, in human urine is described. Special attention is given to the separation from the basic metabolite of droperidol, a drug frequently co-administered with bezitramide.

Liquid chromatography in the monitoring of plasma levels of antiarrhythmic drugs

High-performance liquid chromatography has been employed in the development of assay methods for six antiarrhythmic drugs, disopyramide, lidocain, tocainide, procainamide, aprinidine and quinidine. Liquid-solid chromatography has been used and separation times of about 5 min have usually been sufficient. Owing to the capacity of the liquid chromatographic system, sample preparation has been minimized to a single extraction and direct injection of a considerable part of the extract. The overall time of analysis is very short and the methods are well suited for monitoring of plasma levels of the antirrhythmic drugs and in some instances (procainamide and disopyramide) also for their main metabolites. UV detection at the optimal wavelength has permitted determinations down to 50 pmole (20 ng) in 1 ml of plasma for the amines with high absorbance.