Technical considerations in the gas chromatographic analysis of desipramine

UV-photodegradation of desipramine: Impact of concentration, pH and temperature on formation of products including their biodegradability and toxicity

Desipramine (DMI) is a widely used tricyclic antidepressant, and it is the major metabolite of imipramine (IMI) and lofepramine (LMI); IMI and LMI are two of the most commonly used tricyclic antidepressants. If DMI enters the aquatic environment, it can be transformed by the environmental bacteria or UV radiation. Therefore, photolysis of DMI in water was performed using a simulated sunlight Xenon-lamp and a UV-lamp. Subsequently, the biodegradability of DMI and its photo-transformation products (PTPs) formed during its UV photolysis was studied. The influence of variable conditions, such as initial DMI concentration, solution pH, and temperature, on DMI UV photolysis behavior was also studied. The degree of mineralization of DMI and its PTPs was monitored. A Shimadzu HPLC-UV apparatus was used to follow the kinetic profile of DMI during UV-irradiation; after that, ion-trap and high-resolution mass spectrometry coupled with chromatography were used to monitor and identify the possible PTPs. The environmentally relevant properties and selected toxicity properties of DMI and the non-biodegradable PTPs were predicted using different QSAR models. DMI underwent UV photolysis with first-order kinetics. Quantum yields were very low. DOC values indicated that DMI formed new PTPs and was not completely mineralized. Analysis by means of high-resolution mass spectrometry revealed that the photolysis of DMI followed three main photolysis pathways: isomerization, hydroxylation, and ring opening. The photolysis rate was inversely proportional to initial DMI concentration. The pH showed a significant impact on the photolysis rate of DMI, and on the PTPs in terms of both formation kinetics and mechanisms. Although temperature was expected to increase the photolysis rate, it showed a non-significant impact in this study. Results from biodegradation tests and QSAR analysis revealed that DMI and its PTPs are not readily biodegradable and that some PTPs may be human and/or eco-toxic, so they may pose a risk to the environment.

Prevention of tricyclic antidepressant adsorption loss with diethylamine during solvent evaporation

The authors evaluated the adsorption loss of tricyclic antidepressants in analytical procedures with solvent extraction and evaporation. In standard procedures with the use of triple solvent extraction between alkalinized and acidified samples before chromatographic analysis, the adsorption loss was more significant with the demethylated metabolites. As much as 50% adsorption loss can occur; this irreversible loss can be accounted for entirely during the solvent evaporation step. Because of differential adsorption loss among parent drugs, metabolites, and internal standards, the analytical methods usually had wide within-day and day-to-day variations. The authors found that the addition of as little as 0.05% diethylamine to the extract before evaporation completely eliminated the adsorption loss of amitriptyline-nortriptyline, imipramine-desipramine, and doxepin-desmethyldoxepin. with subsequent improvement in procedure performance. This simple modification can be adopted readily by all laboratories that use solvent extraction and subsequent chromatographic analysis of tricyclic antidepressants.

Antidepressants in serum determined by isolation with two on-line sorbent cartridges and liquid chromatography

A selective method for measuring tricyclic antidepressants in serum is reported. A single assay can be done within ca. 30 min and eight samples can be assayed in less than 150 min. A 1-ml serum sample was diluted and the drugs were extracted from it by passage through a graphitized carbon black (Carbopack B) cartridge. After one washing, this cartridge was connected on line to another one containing a silica-based strong acid exchanger. The tricyclics were removed from the Carbopack surface and selectively readsorbed onto the cation-exchange surface by passing 4 ml of methylene chloride-methanol (60:40, v/v) through the two cartridges. After another wash, the drugs were desorbed from the cation-exchange surface with 0.8 ml of acetonitrile-methanol-water (72:18:10, v/v) saturated with potassium chloride. An aliquot of this solution was chromatographed on a cyano column, and the absorbance of the effluent was measured at 215 nm. The mean analytical recoveries of tricyclic antidepressants added to serum within the range 10-200 micrograms/l exceeded 90%, except for 8-hydroxyamoxapine (mean recovery 85.3%) and amoxapine (mean recovery 83.8%) at the lowest serum concentration considered.

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.

Reliable routine method for the determination of antidepressant drugs in plasma by high-performance liquid chromatography

We describe a rapid and reliable method using high-performance liquid chromatography for the simultaneous measurement of plasma concentrations of currently prescribed antidepressants and their main metabolites (amitriptyline, nortriptyline, trans-10-hydroxy-nortriptyline, clomipramine, desmethylclomipramine, imipramine, desipramine, zimeldine, norzimeldine, doxepin, desmethyldoxepin, trimipramine and mianserin). The method involves a single extraction of plasma at pH 10.1 with hexane-acetonitrile (98:2), solvent transfer to and evaporation in a disposable glass tube and subsequent chromatography of the residue on a CN bonded-phase column using acetonitrile-methanol-phosphate buffer (pH 7.0) as mobile phase. Protriptyline is used as the internal standard. Calibration curves remain linear up to at least 200 micrograms/l, detection limits are 5 micrograms/l, absolute recoveries are over 92%, and precision (coefficient of variation) is 6.9%. Norzimeldine and 10-hydroxynortriptyline show lower recoveries, protriptyline and 10-hydroxynortriptyline higher detection limits. Adsorption to glassware and chemical decomposition during analysis are shown to be negligible. Psychoactive and other drugs frequently prescribed in combination with anti-depressants have been tested for their chromatographic properties under the same conditions.

Measurement of progabide and its deaminated metabolite in plasma by high-performance liquid chromatography and electrochemical detection

Progabide (4- [[(4-chlorophenyl-5-fluoro-2-hydroxyphenol)-methylene] amino] butanamide) and its deaminated metabolite were measured simultaneously in plasma by high-performance liquid chromatography. Both compounds were extracted from plasma and the molecules were stabilized at the methylene--amino double bond with sodium borohydride reduction. Oxidative electrochemical detection was used for final quantitation. The method was used to measure progabide and progabide acid in plasma from a healthy volunteer who received a single 1200-mg dose of progabide orally. Lower limits of detection for progabide and progabide acid were 30 and 15 ng/ml, respectively. Coefficient of variation was less than 5% for both compounds.

Development of a standardized analysis strategy for basic drugs using ion-pair extraction and high-performance liquid chromatography — I. Philosophy and selection of extraction technique

The first of a series of papers on the development of a standardized analysis strategy for basic drugs explains the possible advantages and philosophy of the strategy. The scheme uses ion-pair extraction with direct injection of the extracts into an HPLC system emanating, from two previously-selected systems. The extraction efficiency of sodium-n-octylsulphate as the ion-pairing reagent is compared with that of di(2-ethylhexyl) phosphoric acid (previously shown to be generally applicable to the extraction of basic drugs). Direct injection of the ion-pair extracts into an HPLC system is possible because retention behaviour is independent of whether the basic drugs are injected as an ion-pair or as a base.

Determination of 2-hydroxydesipramine by high-performance liquid chromatography

A simple reversed-phase high-performance liquid chromatographic assay of 2-hydroxydesipramine (2-OH-DES) in plasma is described, using 2-hydroxyimipramine (2-OH-IMI) as the internal standard. Extraction of the plasma samples by methylene chloride-isoamyl alcohol was followed by back-extraction of 2-OH-DES into acidic phosphate buffer. Precautions include silanizing test tubes and rinsing pipettes to minimize adsorptive loss, and washing with extraction solution to eliminate chromatographic interference peaks. Analyses are carried out by using a high carbon load C-18 column (15%) with phosphate buffer-acetonitrile as the mobile phase at 43 degrees C. Detection of 254 nm was monitored at extended attenuation of 0.001 or 0.002 a.u.f.s. Peak height ratios of 2-OH-DES/2-OH-IMI were linearly correlated with 2-OH-DES concentration between 10 and 100 ng/ml of plasma. Detection limit was 3 ng. Coefficients of variation for within-run and day-to-day studies were 2.2% and 5.0%, respectively. A significant amount of 2-OH-DES was identified from the plasma extract of a psychiatric patient taking a daily dose of desipramine. This assay may be used for monitoring of 2-OH-DES in evaluating clinical side effects and for pharmacokinetics studies.

Sensitive high-performance liquid chromatographic analysis for chloroquine in body fluids. Application to studies of drug resistance in Plasmodium falciparum

A high-performance liquid chromatographic method has been developed for the sensitive determination of chloroquine in body fluids. THe method has been applied to quality-control assay of World Health Organization (WHO) In-Vitro, Macro-Test Kits for the assessment of susceptibility of Plasmodium falciparum to chloroquine. Experiments utilizing [14C] chloroquine demonstrated that water was not capable of efficiently desorbing chloroquine from the inside surfaces of kit vials. The addition of blood to the vials effectively desorbs chloroquine. Subsequent addition of the blood to aqueous base followed by hexane extraction permits quantitation by reversed-phase, ion-pair high-performance liquid chromatography utilizing ultraviolet detection at 344 nm. The method is capable of determining as little as 20 ng of chloroquine per vial. This method, utilizing the methyl ether of 9-anthra cenemethanol as internal standard, can quantify chloroquine in 1 ml of blood or urine with a minimum detection limit of 20 ppb (ng/ml). Measurement of blood levels of chloroquine in persons contracting falciparum malaria while following a prophylactic regimen complements in-vitro drug susceptibility measurements in characterizing resistant strains of the parasite.