Determination of clindamycin in plasma or serum by high-performance liquid chromatography with ultraviolet detection

A simple, sensitive high-performance liquid chromatographic assay for the determination of clindamycin in human plasma or serum has long been hampered by inability to separate it from endogenous compounds. We describe here such an assay. Proteins from a 200-microliters sample were precipitated by addition of acetonitrile containing the internal standard, triazolam. The sample was then vortex-mixed and centrifuged at approximately 3000 g for 10 min. The supernatant was evaporated to about 250 microliters under nitrogen, and 10-30 microliters were analyzed using an autoinjector. An octadecylsilane column with acetonitrile-water-phosphoric acid-tetramethylammonium chloride as mobile phase and ultraviolet detection at 198 nm provided a reproducibly quantifiable peak corresponding to 0.17 micrograms/ml. Retention times for clindamycin and triazolam averaged 8 and 11.8 min, respectively. Replicate standard curves run over a 36-h period showed no loss of integrity; r2 values generally exceeded 0.999. The method has successfully been applied to the analysis of samples taken up to 12 h after administration of intravenous infusions of 600-1200 mg in healthy volunteers.     

Determination of morphine 3-esters in rabbit plasma by high-performance liquid chromatography with ultraviolet detection

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of the morphine 3-esters 1[3-(2, 2-dimethylvaleroyl)-morphine (A), 3-(2-phenylbenzoyl)-morphine (B) and 3-(2,2-diphenylpropionyl)-morphine (C)] in rabbit plasma is described. Sample preparation was based on reversed-phase solid-phase extraction. The compounds were separated on C(18) reversed-phase analytical columns and then determined by ultraviolet detection. The recovery from plasma was 78.7 +/- 7.4%, 69.1 +/- 6.9% and 75 +/- 7.2% (mean +/- SD) for A, B, and C, respectively. The present method enabled the detection limit of 0.2, 0.2 and 0.1 ng and quantification limit of 20, 10 and 10 ng/ml for A, B and C, respectively. The developed method was used for determination of the plasmakinetics of these morphine 3-esters in rabbits.     

Determination of pindolol in human plasma and urine by high-performance liquid chromatography with ultraviolet detection

This paper presents a rapid, simple and economical method for assaying pindolol concentrations in plasma and urine by high-performance liquid chromatography using ultraviolet detection. It is sensitive enough for use in single-dose pharmacokinetic studies and may also be used to determine pindolol concentrations in the plasma from patients taking the drug, provided that the patient is not taking any of the drugs which interfere with the method. Drugs which were found to interfere with the pindolol peak are quinidine, n-acetylprocainamide and lidocaine. Disopyramide, oxprenolol and levobunolol interfered with the internal standard peak.     

Determination of dextromoramide in plasma and whole blood using high-performance liquid chromatography with ultraviolet absorbance detection.

Dextromoramide was determined in plasma and whole blood after solid-phase isolation by high-performance liquid chromatography using dextropropoxyphene as internal standard and ultraviolet detection at 215 nm. Owing to its good selectivity, sensitivity and reproducibility, the technique is available for forensic toxicology purposes as well as for clinical pharmacology. The concentrations of dextromoramide were determined in three cancer patients receiving intravenous treatment with one to three 5-mg daily doses. On the fourth day the plasma level was 13.85 +/- 3.27 ng ml-1 just before the first daily dose and 84.28 +/- 12.60 ng ml-1 30 min after dosing. The whole blood concentration, determined in one of the patients, was undetectable just before the dose and was 76 ng ml-1 30 min after dosing.     

Determination of different species of homocysteine in human plasma by high-performance liquid chromatography with ultraviolet detection

This assay measures reduced, free oxidized, protein-bound, and total homocysteine in human plasma. Oxidized species of homocysteine are converted to reduced form by sodium borohydride, and, after precolumn derivatization with 2-chloro-1-methylquinolinium tetrafluoroborate, homocysteine 2-S-quinolinium derivative is separated from those of other plasma thiol derivatives, and quantitated by ion-paired reversed-phase high-performance liquid chromatography with ultraviolet detection. The reduced homocysteine sulfhydryl groups are trapped with minimal oxidation by derivatizing blood samples at the time of collection. With the use of this precise and sensitive HPLC method utilizing popular ultraviolet detection, homocysteine in plasma can be detected and quantitated at the level of 0.1 and 0.2 for reduced fraction, and 0.3 and 0.5 nmol/ml for total homocysteine, respectively. The method is applied for determination of different fractions of homocysteine in plasma of apparently healthy men and women.     

Determination of diclofenac in plasma by high-performance liquid chromatography with electrochemical detection

A reversed-phase high-performance liquid chromatographic method with electrochemical detection for the quantitative determination of diclofenac potassium in plasma was developed. Naproxen was used as the internal standard. The drug and internal standard were isolated from plasma by extraction with dichloromethane and 2 M hydrochloric acid. Chromatographic separation was performed on a C18 column with methanol-water (68:32, v/v) adjusted to pH 3.2 with phosphoric acid as mobile phase. The oxidation potential for detection was established by constructing a voltammogram for diclofenac. The quantification limit for diclofenac in plasma was 5 ng mL(-1). Linearity of the method was confirmed in the range 5-2000 ng mL(-1), correlation coefficient 0.9998. Within-day relative standard deviations (RSDs) ranged from 0.66 to 14.00% and between-day RSDs from 0.59 to 15.78%. The method was successfully applied for the determination of pharmacokinetic parameters after ingestion of a 50 mg dose of diclofenac. Studies were performed on 18 healthy volunteers of both sexes.