Determination of imipenem in human plasma, urine and tissue by high-performance liquid chromatography

A simple and reliable HPLC method is described for the new beta-lactam antibiotic imipenem; suitable extraction procedures for the drug in human plasma, urine and prostatic tissue are described. The figures of merit for the assays are reported and examples given of their application.     

Determination of a new phosphodiesterase V inhibitor,DA-8159, in plasma and urine by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method using liquid-liquid extraction for sample preparation was developed for the determination of a new phosphodiesterase V inhibitor, DA-8159, in rat plasma and urine using sildenafil citrate as an internal standard. A 100 microl aliquot of 0.1 M Na(2)CO(3) (containing sildenafil citrate, 3 microg/ml as free sildenafil) and a 1 ml aliquot of ether were added to a 100 microl aliquot of biological samples (urine samples were diluted 20 times with distilled water). After vortex centrifugation at 9000 x g for 3 min, the ether layer was collected and dried under nitrogen gas. The residue was reconstituted with a 150 microl aliquot of the mobile phase, centrifuged, and a 100 microl aliquot of the supernatant was injected onto a reversed-phase column. The mobile phases, 20 mM KH(2)PO(4) (pH 4.7):acetonitrile (70:30, v/v for plasma and tissue samples, and 75:25, v/v for urine samples), were run at a flow rate of 1.0 ml/min. The column effluent was monitored by an ultraviolet detector set at 292 nm. The retention times for DA-8159 and the internal standard were approximately 10.7 and 9.1 min, respectively, in plasma and tissue samples and the corresponding values in urine samples were 47 and 33 min. The detection limits for DA-8159 in rat plasma and urine were 20 and 100 ng/ml, respectively. The coefficients of variation of the assay were generally low: below 10% for plasma and 9.9% for urine. No interferences from endogenous substances were found.     

Determination of a new reversible proton pump inhibitor,DBM-819, in human plasma and urine,and rat tissue homogenates by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed for the determination of a new proton pump inhibitor, DBM-819, in human plasma and urine and rat tissue homogenates using KR-60461 as an internal standard. A 100-microl aliquot of acetonitrile (containing 0.5 microg/ml of the internal standard) and a 200-microl aliquot of 0.1 M Na(2)HPO(4) (adjusted pH 11 with 1 N NaOH) were added to a 100-microl aliquot of biological sample. After vortex-mixing, the mixture was extracted with 1 ml of ethylacetate. After centrifugation at 12000 x g for 3 min, the organic layer was collected and evaporated under nitrogen gas. The residue was then reconstituted with a 100-microl aliquot of mobile phase, and a 40-microl aliquot was injected onto the HPLC column. The mobile phase, 0.02 M phosphate buffer (pH 5): acetonitrile: methanol (46:44:10, v/v/v), was run at a flow rate of 0.5 ml/min and the column effluent was monitored by the fluorescence detector set at an excitation wavelength of 340 nm and an emission wavelength of 470 nm. The retention times for DBM-819 and the internal standard were approximately 10.5 and 12 min, respectively. The detection limits of DBM-819 in human plasma and urine, and rat tissue homogenates were 0.01, 0.02 and 0.02 (or 0.05) microg/ml. respectively. The coefficients of variation (CV) of the assay were below 11% for human plasma and urine, and rat tissue homogenates. No interferences from endogenous substances were found.     

高效液相色谱法测定注射用法罗培南在健康人血浆和尿中的浓度

目的:建立测定人血浆和尿中注射用法罗培南浓度的高效液相色谱(HPLC)法。方法:血浆样品经10%三氯醋酸沉淀蛋白,尿样直接稀释,以替硝唑为内标,采用乙腈:0.05 mol·L~(-1)磷酸二氢钾缓冲液(pH 3.5,16:84,V:V)为流动相,经Zorbax XDB-C_8柱分离,318 nm波长检测。结果:法罗培南的血浆样品和尿样线性范围分别为0.1～50 mg·L~(-1)和0.5～250 mg·L~(-1),提取回收率分别为51.2%～54.9%和99.6%～104%,日内、日间精密度(RSD)均低于9.14%。结论:本方法准确性好、操作简单,可满足药动学研究的要求。     

Determination of gabapentin in human plasma and urine by high-performance liquid chromatography with UV-vis detection

A simple and reliable high-performance liquid chromatographic (HPLC) method with UV–vis detection has been developed and validated for the determination of gabapentin (GBP) in human plasma and urine. The clean up of the sample was carried out by solid-phase extraction with C18-cartridge. After the clean up procedure, the samples were pre-column derivatizated with 1,2-naphthoquinone-4-sulphonic acid sodium salt (NQS). A chromatographic separation was achieved on a C18 column with a mobile phase consisting of acetonitrile and 10 mM orthophosphoric acid (pH 2.5) with isocratic elution (35:65). Baclofen was used as an internal standard (I.S.). The method developed for GBP was linear over the concentration range of 0.05–5.0 μg/ml and 0.1–10.0 μg/ml for plasma and urine, respectively. The method is precise (relative standard deviation, R.S.D. <4.05%) and accurate (relative mean error, RME <0.15%); mean absolute recoveries were 72.21% for plasma and 72.73% for urine.     

Inhibition of human erythrocyte and gastroduodenal catechol-O-methyltransferase activity by nitecapone

Summary The effect of increasing single oral doses of the novel catechol-O-methyltransferase (COMT) inhibitor, nitecapone, on enzyme activity in red cells (RBC) and gastroduodenal COMT activity has been studied in healthy male volunteers.A dose-dependent decrease in RBC COMT activity was seen in all cases after 1 to 150 mg of the drug. The highest dose of 300 mg did not produce much more inhibition of COMT than 150 mg. The inhibition was not complete; at the highest doses the COMT activity was reduced by 50–60%. The effect and the duration of the inhibition in RBC COMT was strongly correlated with plasma nitecapone concentrations in the dose range up to 150 mg. RBC COMT activity recovered fully in 4 h after medication.Gastric mucosal COMT activity was several-fold higher than that in RBCs. It was also dose-dependently inhibited at the two doses (25 and 100 mg) studied. The inhibition of gastric and duodenal COMT was greater than that in RBCs. This also indicates that nitecapone is locally active in the gastroduodenal tract.The results confirm nitecapone as a potent COMT inhibitor in human tissues. New COMT inhibitors may provide a valuable approach to the treatment of Parkinson's disease in combination with L-dopa and dopa decarboxylase inhibitor therapy.     

The equine metabolism of the catechol-O-methyltransferase enzyme inhibitor nitecapone

The abuse of performance-enhancing catecholamine-based stimulants, such as levodopa, is controlled in horse racing through the application of a regulatory threshold for the common major metabolite. However, catechol-O-methyltransferase (COMT) enzyme inhibitors can be used to restrict the catalysis of the stimulant, and so the concurrent administration of both substances would be a viable strategy to enhance racing performance while removing the risk of exceeding the threshold. A 200 mg dose of nitecapone, a COMT inhibitor, was administered to a Thoroughbred horse, and we have analysed the blood (≤24 h) and urine (≤48 h) samples that were collected. The extracts, analysed by UHPLC coupled to a high-resolution accurate mass spectrometer, were consistent with the presence of nitecapone glucuronide in all the samples collected. An in-depth examination of the samples was then carried out using targeted accurate mass extracted ion chromatograms to identify whether the metabolites that have been found in other species were also present in the extracts. Once these were tentatively identified, MS/MS experiments were conducted on some of the metabolites (M1–M5), as well as decomposition products (DP1 and DP2), to verify that spectrum included MS fragments were consistent with their proposed structures. The accumulated data provided evidence that is consistent with this drug having been converted into many metabolites and a few decomposition products. An unexpected finding was that O-methylation was a very minor pathway until after the reduction of the 2,4-pentanedione side chain had occurred.     

Determination of pentamidine in whole blood, plasma, and urine by high-performance liquid chromatography

The analysis of pentamidine in whole blood, plasma, and urine by liquid chromatography is described. Extraction was made with a mixture of acetonitrile and chloroform followed by back-extraction into phosphate buffer. A reversed-phase chromatographic system with fluorescence detection was used. The precision of the method was 5-7% at the lower limit of determination (16 nmol/L in plasma and hemolyzed whole blood, 27.7 nmol/L in urine).     

Determination of pivaloylcarnitine in human plasma and urine by high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic (HPLC) method was developed for the determination of pivaloylcarnitine, one of the major metabolites of pivaloyloxymethyl (+)-(6R,7R)-7-[(Z)-2-(2-amino-4-thiazolyl)-2- pentenamido]-3-carbamoyloxymethyl-8-oxo-5-thia-1-azabicyclo[4.2.0] oct-2- ene-2-carboxylate hydrochloride hydrate (S-1108), an oral cephem antibiotic, in human plasma and urine. Fluorescence detection was done with 3-bromomethyl-6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone as the labeling reagent. Pivaloylcarnitine and cyclopropylacetylcarnitine, the internal standard, were selectively fractionated from plasma or urine on a disposable cation-exchange column. Derivatization was completed in 20 min at 40 degrees C in the presence of N,N'-diisopropylethylamine as the catalyst. A column-switching device was used to remove the excess reagent for HPLC analysis. The recovery of pivaloylcarnitine was greater than 98%, and average within-day and between-day coefficients of variation were less than 5% at concentration ranges of 0.05-2 micrograms/mL for plasma and 5-500 micrograms/mL for urine. Detection limits were 0.02 micrograms/mL for plasma and 1 micrograms/mL for urine. The urinary recovery of pivaloylcarnitine was 94% after the administration of S-1108, a result that suggested that S-1108 was almost quantitatively converted to pivalic acid and then conjugated with carnitine.     

Liquid chromatographic determination of a new catechol-O-methyltransferase inhibitor, entacapone, and its Z-isomer in human plasma and urine.

Assay procedures for analysis of entacapone, (E)-2-cyano-N,N-diethyl-3-(3,4-dihydroxy-5-nitrophenyl)-propenamide++ +, and its Z-isomer in human plasma and urine are described. The methods were based on reversed-phase liquid chromatography with amperometric detection. Entacapone and its Z-isomer were extracted with n-hexane-ethyl acetate mixtures after acidification with hydrochloric acid. From urine extracts the analytes were back-extracted into phosphate buffer (pH 7.2). During sample treatment 1-2% of entacapone was changed to the Z-isomer. With recoveries exceeding 75% the relative standard deviations for within-day precision were less than 11% for plasma and less than 6% for urine at the quantitation limit (10 ng ml-1) and less than 6% for both methods at higher concentrations (20-2000 ng ml-1). The assays were specific with respect to all known metabolites and selective, sensitive and precise enough for determination of entacapone and its Z-isomer in plasma and urine down to 10 ng ml-1. The methods are thus suitable for the kind of pharmacokinetic studies exemplified in this paper.     

Determination of procaine in equine plasma and urine by high-performance liquid chromatography.

The variability in plasma and urine equine procaine measurement between three independent laboratories using current methods led to the development of a sensitive, reliable, and reproducible high-performance liquid chromatographic method. Standardbred mares were administered either a penicillin G procaine preparation intramuscularly or procaine hydrochloride subcutaneously, and blood and urine were collected at defined time intervals. By HPLC the detection limits for procaine in plasma and urine were 1 and 10 ng/mL, respectively. In contrast procaine in plasma could not be detected by GC-NPD, while the urinary detection limit was 50 ng/mL. The concentration of fluoride in the collection tubes and repetitive freeze-thawing modified plasma procaine measurement. Urinary pH was a factor in estimation of urine procaine levels with greater recovery and reproducibility of results at pH 5 as compared to pH 7. This HPLC method provides a simple, sensitive, and reliable quantitation of procaine in equine plasma and urine.     

Determination of MK-0476 in human plasma by liquid chromatography

A simple and accurate assay for quantitating MK-0476 [sodium 1-(((1(R)-(3-(2-(7-chloro-2-quinolinyl)-(E)-ethenyl)phenyl)(3-(2-(1-hydroxy-1-methylethyl)phenyl)propyl)thio)-methyl)cyclopropane)acetate], which is a potent and selective leukotriene D₄-receptor antagonist, in human plasma has been developed. The method involves precipitation of protein and reversed-phase liquid chromatography with fluorescence detection. The assay is linear in the range of 30–3000 ng ml⁻¹ of MK-0476, and the limit of detection is 5 ng ml⁻¹. The interday precision (% relative standard deviation) values of this method at 51 and 2040 ng ml⁻¹ are 10 and 3%, respectively. The interday accuracy values at these concentrations are 94 and 104%, respectively. The absolute recovery of MK-0476 is 99%. The utility of this method to determine plasma concentrations of MK-0476 in humans receiving the drug orally was demonstrated.     

高效液相色谱法测定人血浆中左布比卡因的浓度

目的建立高效液相色谱法测定人血浆中左布比卡因的浓度。方法以罗哌卡因为内标,色谱柱为Hypersil C_(18)柱(200 mm×4.6 mm,5μm),流动相采用0.01 mol·L~(-1)磷酸二氢钾-乙腈(87:13,V:V,pH=3.4),流速2.0 mL·min~(-1),检测波长为210 nm,柱温40℃。结果标准曲线方程为Y=0.310 1 X+ 0.008 9,r=0.999 7,左布比卡因的质量浓度在0.012 5～2 mg·L~(-1)范围内呈良好的线性关系,最低检测限为0.01 mg·L~(-1);方法回收率在96%～105%之间;日间、日内精密度RSD均<5%。结论本方法可用于临床上左布比卡因血药浓度的监测和药动学研究。     

高效液相色谱法测定血浆中氟哌啶醇浓度

目的：建立高效液相色谱法测定血浆中氟哌啶醇浓度的方法。方法：以乙腈甲醇０ ．０２５ｍｏｌ／Ｌ 磷酸二氢钾（４５∶５∶５０ ,ｖ／ｖ） 为流动相,氯氟哌啶醇作内标,紫外波长２４８ｎｍ 处检测。结果：血浆中氟哌啶醇的最低检测浓度为０ ．５ｎｇ／ｍｌ,平均提取回收率为８６ ．６ ％ ±４ ．９ ％ ,线性范围１ ～５０ｎｇ／ｍｌ（ｒ ＝ ０ ．９９９８） ,日内和日间ＲＳＤ 分别小于８ ％ 和９ ％ 。结论：方法灵敏、快速、准确,可满足临床治疗药物的监测工作     

高效液相色谱法测定人血中表阿霉素的浓度

目的:建立人血浆中表阿霉素的HPLC测定方法。方法:采用Hypersil ODS-C18柱为分析柱;乙腈-甲醇-水(32∶50∶18,v/v)为流动相,流速为1.0mL.min-1;荧光检测器的激发波长480nm、发射波长560nm;以柔红霉素作为内标,采用沉淀蛋白-脱水法提取样品。结果:表阿霉素、内标与人血浆中其他成分分离良好,在10~1 000μg.L-1的范围内线性良好,r=0.999 1(n=5),回收率为102.63%,日内及日间RSD均小于5%,最低检测限为5μg.L-1。结论:本法取样量小,操作简便快速,适用于临床表阿霉素的血药浓度监测和药动学研究。     

高效液相色谱法测定人血浆中氟罗沙星浓度

目的：建立HPLC方法测定人血浆中氟罗沙星的浓度。方法：取0.1ml血浆样品,二氯甲烷提取,挥干溶剂,残渣加流动相进样;用C18分析柱,以甲醇－20mmol.L^-1磷酸二氢钾－10mmol.L^-1四丁基溴化铵（20：70：10）为流动相,流速：0.8ml.min^-1,紫外检测波长268nm,用峰面积定量。结果：标准曲线在0.25-8μg.ml^-1范围内线性关系良好（r=0.9999),最低检测浓度为0.1μg.ml^-1;方法回收率为95．93％－101．32％,日内RSD＜4％,日间RSD＜8％。结论：本法准确,精密,简便,快速,取样量少,可满足临床血药浓度测试要求。     

Determination of celecoxib in human plasma by high-performance liquid chromatography

A high performance liquid chromatographic method for the quantitation of celecoxib (CEL) in human plasma is presented. The method is based on liquid-liquid extraction with chloroform and reversed-phase chromatography using a Nucleosil CN column (250 mm x 4.6 mm i.d., 5 microm particle size) and UV spectrophotometer detection at 260 nm. The mobile phase consists of acetonitrile:water (60:40 (v/v)). Flutamide was used as internal standard (IS). The assay was linear in the concentration range of 10-1000 ng/ml when 0.5 ml aliquots of plasma were extracted. Within-day and between-day precision expressed by relative standard deviation is less than 4% and inaccuracy does not exceed 3%. The assay was used to analyze samples collected during human clinical studies.     

Rapid determination of atenolol in human plasma and urine by high-pressure liquid chromatography

A rapid, specific, high-pressure liquid chromatographic determination of atenolol in plasma and urine was developed. This method employs the high sensitivity of fluorescence detection together with selective extraction and reversed-phase chromatography to measure concentrations as low as 20 ng of drug/ml of plasma with a coefficient of variation of 3.91%. The assay is specific enough to be valid in the presence of plasma and urine substances. The detection limit (i.e., three times baseline noise) is 3 ng/ml.