Pharmacokinetics and selected pharmacodynamics of trazodone following intravenous and oral administration to horses undergoing fitness training.

OBJECTIVE To measure concentrations of trazodone and its major metabolite in plasma and urine after administration to healthy horses and concurrently assess selected physiologic and behavioral effects of the drug. ANIMALS 11 Thoroughbred horses enrolled in a fitness training program. PROCEDURES In a pilot investigation, 4 horses received trazodone IV (n = 2) or orally (2) to select a dose for the full study; 1 horse received a vehicle control treatment IV. For the full study, trazodone was initially administered IV (1.5 mg/kg) to 6 horses and subsequently given orally (4 mg/kg), with a 5-week washout period between treatments. Blood and urine samples were collected prior to drug administration and at multiple time points up to 48 hours afterward. Samples were analyzed for trazodone and metabolite concentrations, and pharmacokinetic parameters were determined; plasma drug concentrations following IV administration best fit a 3-compartment model. Behavioral and physiologic effects were assessed. RESULTS After IV administration, total clearance of trazodone was 6.85 ± 2.80 mL/min/kg, volume of distribution at steady state was 1.06 ± 0.07 L/kg, and elimination half-life was 8.58 ± 1.88 hours. Terminal phase half-life was 7.11 ± 1.70 hours after oral administration. Horses had signs of aggression and excitation, tremors, and ataxia at the highest IV dose (2 mg/kg) in the pilot investigation. After IV drug administration in the full study (1.5 mg/kg), horses were ataxic and had tremors; sedation was evident after oral administration. CONCLUSIONS AND CLINICAL RELEVANCE Administration of trazodone to horses elicited a wide range of effects. Additional study is warranted before clinical use of trazodone in horses can be recommended.

The trazodone metabolite meta-chlorophenylpiperazine can cause false-positive urine amphetamine immunoassay results.

Amphetamines and methamphetamines are part of an important class of drugs included in most urine drugs of abuse screening panels, and a common assay to detect these drugs is the Amphetamines II immunoassay (Roche Diagnostics). To demonstrate that meta-chlorophenylpiperazine (m-CPP), a trazodone metabolite, cross-reacts in the Amphetamines II assay, we tested reference standards of m-CPP at various concentrations (200 to 20,000 g/L). We also tested real patient urine samples containing m-CPP (detected and quantified by HPLC) with no detectable amphetamine, methamphetamine, or MDMA (demonstrated by GC MS). In both the m-CPP standards and the patient urine samples, we found a strong association between m-CPP concentration and Amphetamines II immunoreactivity (r = 0.990 for the urine samples). Further, we found that patients taking trazodone can produce urine with sufficient m-CPP to result in false-positive Amphetamines II results. At our institution, false-positive amphetamine results occur not infrequently in patients taking trazodone with at least 8 trazodone-associated false-positive results during a single 26-day period. Laboratories should remain cognizant of this interference when interpreting results of this assay.

Trazodone, meta-chlorophenylpiperazine (an hallucinogenic drug and trazodone metabolite), and the hallucinogen trifluoromethylphenylpiperazine cross-react with the EMIT®II ecstasy immunoassay in urine.

A series of patients whose urine screened positive for 3,4-methylenedioxymethamphetamine (MDMA) using a commercial enzyme immunoassay test (Ecstasy EMIT II assay), failed to confirm by substance-specific liquid chromatography-tandem mass spectrometry tests for MDMA. Further evaluation of these urine specimens indicates that they were positive for trazodone and its metabolite meta-chlorophenylpiperazine (m-CPP). Independent tests of standards showed significant crossreactivity on the Ecstasy EMIT II assay with trazodone, m-CPP, and the related recreational drug trifluoromethylphenylpiperazine (TFMPP). This is of further forensic significance because m-CPP is emerging as an illicit recreational drug in its own right or as an adulterant in illicit cocaine and MDMA. The hallucinogen benzylpiperazine was also assessed but found not to cross-react significantly with this assay. Patients taking trazodone may get false-positive results on the urine EMIT test for MDMA.

General unknown screening procedure for the characterization of human drug metabolites in forensic toxicology: applications and constraints.

LC coupled to single (LC-MS) and tandem (LC-MS/MS) mass spectrometry is recognized as the most powerful analytical tools for metabolic studies in drug discovery. In this article, we describe five cases illustrating the utility of screening xenobiotic metabolites in routine analysis of forensic samples using LC-MS/MS. Analyses were performed using a previously published LC-MS/MS general unknown screening (GUS) procedure developed using a hybrid linear IT-tandem mass spectrometer. In each of the cases presented, the presence of metabolites of xenobiotics was suspected after analyzing urine samples. In two cases, the parent drug was also detected and the metabolites were merely useful to confirm drug intake, but in three other cases, metabolite detection was of actual forensic interest. The presented results indicate that: (i) the GUS procedure developed is useful to detect a large variety of drug metabolites, which would have been hardly detected using targeted methods in the context of clinical or forensic toxicology; (ii) metabolite structure can generally be inferred from their "enhanced" product ion scan spectra; and (iii) structure confirmation can be achieved through in vitro metabolic experiments or through the analysis of urine samples from individuals taking the parent drug.

Electro-oxidation and determination of trazodone at multi-walled carbon nanotube-modified glassy carbon electrode.

A simple and rapid electrochemical method was developed for the determination of trace-level trazodone, based on the excellent properties of multi-walled carbon nanotubes (MWCNTs). The MWCNT-modified glassy carbon electrode was constructed and the electrochemical behavior of trazodone was investigated in detail. The cyclic voltammetric results indicate that MWCNT-modified glassy carbon electrode can remarkably enhance electrocatalytic activity towards the oxidation of trazodone in neutral solutions. It leads to a considerable improvement of the anodic peak current for trazodone, and allows the development of a highly sensitive voltammetric sensor for the determination of trazodone. Trazodone could effectively accumulate at this electrode and produce two anodic peaks at about 0.73 V and 1.00 V. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the trazodone determination by differential-pulse voltammetry. Under optimized conditions, the concentration range and detection limit are 0.2-10 microM and 24 nM, respectively for trazodone. The proposed method was successfully applied to trazodone determination in pharmaceutical samples. The analytical performance of this sensor has been evaluated for detection of analyte in urine as a real sample.

Application of a trazodone-selective electrode to pharmaceutical quality control and urine analyses.

A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 x 10(-5)-1 x 10(-2) M) with a mean slope of 59.3 +/- 0.9 mV/dec of concentration, a mean detection limit of 1.8 x 10(-5) +/- 2.2 x 10(-6) M, a wide working pH range (5-7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability, reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite. The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples; no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size, based on a direct potentiometric determination with the new selective electrode is presented as well.

Determination of trazodone in urine and pharmaceuticals using micellar liquid chromatography with fluorescence detection.

A simple and reliable liquid chromatographic procedure is described for the determination of trazodone in pharmaceutical formulations and urine samples. The optimized procedure uses fluorimetric detection, a C18 column and a micellar mobile phase of sodium dodecyl sulfate (SDS) and 1-butanol. The mobile phase selected for use was 0.2M SDS and 8% 1-butanol fixed at pH 3 with phosphate buffer. The total analysis time was 10 min. For the analysis of urine samples, one great advantage of the method is that no extraction step is required. The quantification limit was 9.5 ng mL(-1), ensuring the analysis of the drug in biological fluids. The procedure shows good accuracy, repeatability and selectivity. Repeatability and intermediate precision were tested for several concentrations of the drug. Good claim percentages were obtained in the analysis of pharmaceutical formulations. Calibration repeatability in urine matrix was also studied in the 0.06-22.4 microg mL(-1) range. Good recoveries were obtained from spiked urine samples. No interferences from common additives frequently administered with trazodone or from endogenous compounds in urine samples were found. The results show that the procedure is suitable for routine analysis of the drug.

Piperazine-derived designer drug 1-(3-chlorophenyl)piperazine (mCPP): GC-MS studies on its metabolism and its toxicological detection in rat urine including analytical differentiation from its precursor drugs trazodone and nefazodone.

Studies on the metabolism and the toxicological analysis of the piperazine-derived designer drug 1-(3-chlorophenyl)piperazine (mCPP) in rat urine using gas chromatography-mass spectrometry (GC-MS) are described. mCPP was extensively metabolized, mainly by hydroxylation of the aromatic ring and by degradation of the piperazine moiety to the following metabolites: two hydroxy-mCPP isomers, N-(3-chlorophenyl)ethylenediamine, 3-chloroaniline, and two hydroxy-3-chloroaniline isomers. The hydroxy-mCPP metabolites were partially excreted as the corresponding glucuronides and/or sulfates, and the aniline derivatives were partially acetylated to N-acetyl-hydroxy-3-chloroaniline isomers and N-acetyl-3-chloroaniline. Our systematic toxicological analysis (STA) procedure using full-scan GC-MS after acid hydrolysis, liquid-liquid extraction, and microwave-assisted acetylation allowed the detection of mCPP and its previously mentioned metabolites in rat urine after single administration of a dose calculated from the doses commonly taken by drug users. The hydroxy-mCPP metabolites should be used as target analytes being the major metabolites of mCPP. Assuming similar metabolism, our STA procedure should be suitable for detection of an intake of mCPP in human urine. Furthermore, possibilities for differentiating an intake of mCPP from that of its precursor drugs trazodone or nefazodone, two common antidepressants, are described. Within the context of these studies, N-(3-chlorophenyl)ethylenediamine was identified as a new metabolite of these two antidepressants.

Voltammetric analysis of trazodone HCl in pharmaceuticals and biological fluids.

The voltammetric behavior of trazodone (TRZ) HCl was studied using direct current (DC(t)), differential pulse (DPP) and alternating current (AC(t)) polarography. The drug manifests cathodic waves over the pH range of 10-14. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 10, the diffusion current-concentration relationship was found to be rectilinear over the range 4-32 and 0.8-24 microg ml(-1) using DC(t) and DPP modes, respectively, with minimum detectability (S/N=2) of 0.104 microg ml(-1) (2.45 x 10(-6) M) and 0.314 microg ml(-1) (7.397 x 10(-6) M) using the DPP and DC(t) modes, respectively. The diffusion-current constant (I(d)) is 4.31+/-0.02 (n=6). The proposed method was successfully applied to the determination of the studied compound either in pure form or in formulations. The results obtained were favorably compared with those given using a reference method. Furthermore, the proposed method was applied to the determination of TRZ in spiked human urine and plasma adopting the DPP technique. No prior extraction step is needed in case of urine. The percentage recoveries were 98.43+/-0.79 and 97.44+/-0.705 (n=4) in spiked human urine and plasma, respectively. A pathway for the electrode reaction was postulated.

High-performance liquid chromatographic assay with ultraviolet detection for the determination of etoperidone and two active metabolites, 5-(1-hydroxyethyl) etoperidone and 1-(3-chlorophenyl)piperazine, in plasma.

A selective and sensitive high-performance liquid chromatographic assay with ultraviolet detection for the determination of the antidepressant drug etoperidone and two active metabolites in plasma is described. The drug, metabolites and internal standard are isolated from plasma using a two-step liquid-liquid extraction procedure. The resulting sample is chromatographed on a C18 column (10 cm x 2.1 mm I.D.) with ultraviolet detection at 254 nm. Standard curves are linear for each compound over the concentration range 2-1000 ng/ml. The accuracy and precision of the assay, expressed as the percentage deviation of measured values from the true value and the relative standard deviation (inter-run), are less than or equal to 10% at all concentrations except the minimum quantification limit. Using an automated injector and computerized data acquisition, eighty samples can be routinely processed in one day. The assay has been successfully used for the analysis of plasma samples from pharmacokinetic studies in mice, rats, dogs and humans.

Studies on metabolism of trazodone. III Species differences.

1. After oral administration of (14C) trazodone HCl (4 mg/kg) to rabbits, the blood level of radioactivity shows a peak at 3 h; unchanged trazodone concentration in brain is higher than that in plasma at 3 h after dosage. 29 The metabolic fate of trazodone in rabbits is different from that in rats and a new, basic metabolite is present in rabbit liver, brain, plasma and urine. 3. The concentration pattern in blood of humans given a single dosage (50 mg) of trazodone HCl is similar to that in rabbits rather than that in rats. 4. The rate of metabolism of trazodone by liver microsomes from mice is approximately 1-5 times higher than that with rat or rabbit liver microsomes.