Determination of levamisole, aminorex, and pemoline in plasma by means of liquid chromatography-mass spectrometry and application to a pharmacokinetic study of levamisole.

Levamisole is an anti-helminthic drug and gained forensic interest after it was found that it was used as a cocaine adulterant. A liquid chromatography-mass spectrometry (LC-MS) method for the determination of levamisole and its metabolite aminorex in human plasma is described. Selectivity is given; calibration curves were linear within a calibration range of 1 ng/mL-500 ng/mL. Limits of detection and quantification (LODs, LOQs) were 0.85 ng/mL for levamisole and 0.09 ng/mL, and 0.34 ng/mL for aminorex, respectively. Precision data was in accordance with the GTFCh guidelines. The validated method was successfully applied to study the pharmacokinetics of levamisole after administration of 100 mg of levamisole orally. Levamisole could be detected up to 36 h after ingestion in serum, while aminorex never exceeded the LOQ. A one-compartment model best described levamisole pharmacokinetics. The following parameters were calculated: ka = 1.2 [1/h], CL/F = 52 l/h, V/F = 347 l, f (renal) = 0.0005, t ½ = 2.0 h, AUC = 1923 ng/mL*h, cmax = 214 ng/mL, tmax = 1.98 h. Levamisole could be quantified in 42.5% of cocaine--positive plasma samples (2.2 to 224 ng/mL). Aminorex was positive in only 11.3% of the cases; however, it was never found higher than the LOQ. Pemoline, another stimulant detected in horse urine samples after administration of levamisole, was not found either in serum or in urine of this pharmacokinetic study. In post-mortem cases, levamisole and aminorex could be detected in femoral blood and the urine of cocaine users. Pemoline was not detected.

Chiral separation of pemoline enantiomers by cyclodextrin-modified micellar capillary chromatography.

Micellar electrokinetic chromatography (MEKC) was successfully applied to the chiral separation with the addition of cyclodextrins (CDs) as chiral selector to running buffer. Chiral separation depended on the type of CDs. Mono-3-O-phenylcarbamoyl-beta-CD was effective for the chiral separation of pemoline. We investigated the type and concentration of CD and other parameters such as buffer pH, the concentration of SDS and the effect of organic modifier. The conditions for enantiomeric separation of pemoline were as follows: 40 mmol/l borate buffer at pH 9.0 with 40 mmol/l SDS, 20 mmol/l mono-3-O-phenylcarbamoyl-beta-CD and 10% 2-propanol. Baseline separation (Rs=2.21) of pemoline can be achieved.

Determination of pemoline in plasma, urine and tissues by reversed-phase high-performance liquid chromatography.

A simple and selective high-performance liquid chromatographic method with ultraviolet detection at 215 nm for the determination for pemoline in rat plasma, urine and tissues is described. Pemoline in the samples was extracted with methylene chloride at pH 10 and the organic phase was evaporated after adding 5-methyl-5-phenylhydantoin used as an internal standard. Pemoline and the internal standard were separated on a Kaseisorb LC C8-60-5 reversed-phase column. The limits of determination of pemoline in 0.1-0.2 ml of plasma, urine and tissue homogenates were 2, 100 and 20 ng, respectively. The method should be useful for studies of the pharmacokinetics and distribution of pemoline in small animals.

Determination of pemoline in plasma, plasma water, mixed saliva, and urine by high-performance liquid chromatography.

A new determination method of pemoline in plasma, plasma water, mixed saliva, and urine using high-performance liquid chromatography was developed. The detection limit of pemoline using 0.2 ml of the sample was 0.02 microgram/ml in plasma, plasma water, saliva, and urine. The recoveries of pemoline added to plasma, saliva, and urine (each 6 micrograms/ml) were more than 98%. The coefficients of variation of within-run and between-run precisions for 5 concentrations of pemoline in plasma were less than 5 and 6%, respectively. The elimination half-lives of pemoline obtained from the plasma concentration-time curves after a single oral administration of pemoline in two subjects were 6.7 and 10.3 h. Mean values of the ratio between saliva and plasma total concentration in two subjects were 0.55 and 0.64, and mean values of plasma protein binding percent were 35.7 and 25.2%, respectively. The saliva concentrations were in proportion to the plasma unbound pemoline concentrations at simultaneous samplings, and the ratios between saliva and plasma unbound concentration were about 0.9 in two subjects. Usefulness of saliva in the estimation of plasma protein-unbound pemoline concentration was noted.

Sensitive GLC assay for pemoline in biological fluids using nitrogen-specific detection.

Extractive alkylation was used to determine intact pemoline in serum and urine. Pemoline was extracted into methylene chloride as an ion-pair with tetrapentylammonium hydroxide under alkaline conditions. Evaporation of the solvent at 70 degrees in the presence of methyl iodide yielded the N,N-dimethylpemoline derivative. GLC analysis was performed on a 5% FFAP column with nitrogen-specific detection. Sensitivity was 0.05 microgram/ml with 1 ml of urine of serum. Calibration curves were linear to at least 4 microgram/ml with serum and 15 microgram/ml with urine. Precision was excellent with a pooled relative standard deviation of +/- 7.5% for serum samples in a 0.1-4 microgram/ml range.

Assay of pemoline in human plasma, saliva and urine by capillary gas chromatography with nitrogen-selective detection.

A simple gas chromatographic assay of the psycho-stimulant pemoline in human urine, plasma and saliva has been developed. Instead of direct extraction of the drug from urine, plasma and saliva, it is hydrolyzed to 5-phenyl-2,4-oxazolidine-dione with 1 N hydrochloric acid. After extraction this compound is methylated with diazomethane and determined by gas-liquid chromatography using a capillary SCOT column with a mixed stationary phase, a solid injection system and a nitrogen-selective detector. 5-Phenyl-2,4-oxazolidinedione, which was also found to be a metabolite of pemoline, could be determined quantitatively in human urine.

GLC determination of pemoline in biological fluids.

A specific GLC method for the determination of microgram quantities of the central stimulant pemoline in biological fluids is described. Extraction problems due to the low solubility of pemoline are avoided by acid hydrolysis of the drug to 5-phenyl-2,4-oxazolidinedione, which then can be easily isolated by two-phase extraction with dichloromethane, ether, or chloroform. Amide-imide tautomerism enables a cleanup of the extract. Quantitative determination at the microgram level is done on a methylated fraction of the dichloromethane extract by GLC using a suitable internal standard. For supporting evidence of the GLC method's specificity, the compound is also identified by examining an aliquot of the final dichloromethane extract by TLC.

Gas chromatographic determination of pemoline in biological fluids using electron capture detection.

A simple and sensitive gas chromatographic (GC) method for the determination of pemoline in biological fluids, utilizing electron capture detection is described. Plasma samples with a pemoline analog added as internal standard were deproteinized with sulfosalicylic acid, and the supernatants were heated at 80 degrees. The pemoline-dione formed was extracted with benzene, and the extract was analyzed on a gas chromatograph equipped with a tritium foil electron capture detector. Poly A-103 (3%) on Gas-Chrom Q (100-120 mesh) packed in a 3-ft. silanized glass column was used as the stationary phase, with nitrogen serving as carrier gass. Under the same GC conditions, benzene extracts of pemoline-dione from acid-hydrolyzed urine samples were analyzed. Us-ng 1 ml of plasma or urine, the lower limit for the assay was about 0.1 microgram/ml. The method is accurate and reproducible, with a relative standard deviation with +/-4%. Mandelic acid (a metabolite of pemoline) does not interfere with the assay.

Combined gas-liquid chromatographic-mass spectrometric analysis of pemoline in biological samples.

A description is given of a gas-liquid chromatographic (GLC) method for the detection and determination of pemoline in biological samples. On treatment with hydrochloric acid, pemoline is converted into 5-phenyl-2,4-dioxooxazolidine, an acidic compound, which can be easily extracted with dichloromethane and determined by GLC. A combined GLC-mass spectrometric method is described.

The application of quadrupole mass filters in field desorption mass spectrometry.

The advantages and limitations which quadrupole mass filters afford to the field desorption technique with respect to use for routine work are discussed and experimentally confirmed by the analyses of some drugs using a field desorption quadrupole mass spectrometer. The possibility of fast identification of drug intoxication is demonstrated by the analysis of the chloroform extract of urine in a case of overdose of hypnotics.

Pemoline levels in brain: enhancement by dimethyl sulfoxide.

Pemoline-C(14) dissolved in dimethyl sulfoxide and injected intraperitoneally into rats was found in larger amounts in the brain than was a similar dose given in 0.3 percent tragacanth suspension. This appeared to be related to a partial breakdown of the blood-brain barrier in vivo by the dimethyl sulfoxide.