Determination of 2',3'-dideoxycytidine in maternal plasma, amniotic fluid, placental and fetal tissues by high-performance liquid chromatography.

2',3'-Dideoxycytidine (DDC) is a nucleoside reverse transcriptase inhibitor that has been shown to inhibit the human immunodeficiency virus (HIV). DDC is a candidate for treatment of pregnant women to prevent prenatal transmission of HIV/AIDS to their unborn children. A quick and simple high-performance liquid chromatography (HPLC) method has been developed and validated for the determination of DDC concentrations in samples collected from a pregnant rat model (maternal plasma, amniotic fluid, placental and fetal tissues). Extraction of DDC and its internal standard 2',3'-dideoxy-3'-thiacytidine (3TC) in plasma and amniotic fluid was carried out by protein precipitation. Extraction from placental and fetal homogenates was achieved by solid phase extraction using Waters Oasis HLB solid phase extraction cartridges. Chromatographic separation was achieved on a Waters Spherisorb S3W silica column (4.6 mm x 100 mm) equipped with a Phenomenex guard column. The mobile phase used was 10% methanol in water with 22 mM formic acid. The flow rate was 0.5 ml/min, and the detection wavelength was optimized at 275 nm. Under these chromatographic conditions, DDC eluted around 12 min, and 3TC eluted around 10 min. The calibration curves for each day of validation and analysis showed good linear response through the range of 0.15-75.0 microg/ml in each of the four matrices. The relative recovery for DDC in each of the matrices ranged from 87.8% to 103.0%. Acceptable intra- and inter-day assay precision (<15% R.S.D.) and accuracy (<15% error) were observed over 0.15-75.0 microg/ml for all four matrices.

Validated RP-hPLC method for the assay of zalcitabine in drug substance, formulated products and human serum.

A HPLC method for zalcitabine determination in bulk form, pharmaceutical dosage forms and human serum has been developed and validated. The proposed method was conducted using a reverse phase technique, and UV monitoring at 265 nm. The mobile phase consisted of methanol: 0.01 M NaH2PO4 (85:15; v/v) adjusted to pH 4.62 with 1 M NaOH. The detector response was linear in the range of 0.015-50 microg mL(-1). The limit of detection and the limit of quantification of the procedure were 0.0066 microg mL(-1) and 0.022 microg mL(-1), respectively. The retention time was 2.5 min for zalcitabine and 3.5 min for the internal standard. No interferences from tablet additives were observed and analysing tablets containing zalcitabine proved the applicability of the method. This method was also applied for the determination of zalcitabine in spiked human serum samples.

Application of a radioimmunoassay for determination of levels of zalcitabine (ddC) in human plasma, urine, and cerebrospinal fluid.

A specific and sensitive radioimmunoassay for the determination of levels of zalcitabine in human plasma, urine, and cerebrospinal fluid has been developed. Commercially available radiolabel and antiserum (Sigma Chemicals) were used after dilution in assay buffer. Prior to the immunoassay, standard and patient samples were subjected to solid-phase extraction on silica columns in order to obtain purified samples. The lower limit of quantitation was determined to be 1 ng/ml. Intra- and interassay variations were less than 11% for a number of quality control samples of drug in plasma and urine. Results from parallelism studies with plasma and urine demonstrated that samples outside the standard range (1 to 30 ng/ml) could be diluted by blank plasma or assay buffer, respectively. A large number of related compounds and potentially coadministered drugs were tested for cross-reactivity. Stability tests showed that heat treatment for 30 min at 60 degrees C or storage for 1 month at -30 degrees C did not affect zalcitabine concentrations in plasma or urine. The radioimmunoassay with solid-phase extraction for sample cleanup discussed here has been successfully applied in a pharmacokinetic study of a single patient, demonstrating its applicability for clinical pharmacokinetic research with zalcitabine.

Automated high-performance liquid chromatographic analysis of (-)-2'-deoxy-3'-thiacytidine in biological fluids using the automated sequential trace enrichment of dialysate systems.

A fully automated HPLC procedure was developed for the analysis of a small volume of perfusion solutions from an isolated perfused rat kidney study. The method involved separation of (-)-2'-deoxy-3'-thiacytidine (3TC) from the matrix by dialysis with 10 mM potassium phosphate buffer pH 3.0. 3TC was subsequently separated from the dialysate as it flowed through a SCX cation-exchange cartridge. The trapped 3TC was then eluted with a mobile phase of 50 mM ammonium acetate buffer (pH 5.5)-methanol (90.5:9.5, v/v) at a flow-rate of 1.0 ml/min for 2 min. The eluent was directed to the HPLC system and chromatographed with a BDS C18 analytical column at a temperature of 45 degrees C. Detection of 3TC was carried out by UV absorption at 274 nm. The procedure was validated from 25 to 10,000 ng/ml. Coefficients of variance (C.V.) of 3TC quality control samples were less than 9%. C.V.s of the standard curve samples were also less than 10% except for the 25 ng/ml samples (11.5%). The mean interpolated concentrations were within 8% of the nominal concentrations for all samples. No interference from concurrent drugs was observed. Preliminary results suggested that this procedure may also be used for human serum and urine samples.

Determination of 3'-azido-3'-deoxythymidine, 2',3'-dideoxycytidine, 3'-fluoro-3'-deoxythymidine and 2',3'-dideoxyinosine in biological samples by high-performance liquid chromatography.

A simple and fast high-performance liquid chromatographic assay for the determination of 3'-azido-3'-deoxythymidine (AZT), 2',3'-dideoxycytidine (ddC), 3'-fluoro-3'-deoxythymidine (FT) and 2',3'-dideoxy-inosine (ddI) in complex biological matrices is described. The method allows rapid nucleoside determination using a phenyl column within extra- as well as intracellular media without further sample pretreatment and extraction procedures. The lower limit of detection is ca. 0.05 micrograms/ml for each nucleoside, and the separation can easily be optimized for AZT, ddC, FT and ddI by variation of the methanolic part of the mobile phase and the detector wavelengths.