Simple high-performance liquid chromatographic assay for the determination of ciprofloxacin in human plasma with ultraviolet detection.

A simple high-performance liquid chromatographic method is described for the quantitative analysis of ciprofloxacin in human plasma. Following protein precipitation from plasma by means of 6% perchloric acid, the upper layer which contains the analyte and the internal standard lomefloxacin, was analysed on a reverse phase column LiChrospher 60 RP-select B (5 microm) (EcoCART 125-3) with ultraviolet detection at 280 nm. The mobile phase was acetic acid 5%-methanol-acetonitrile (90:5:5, v/v/v). The assay was linear for ciprofloxacin over the concentration range of 0.050 to 6.00 microg ml(-1). The limit of quantification (LOQ) was 0.050 microg ml(-1). The method was successfully applied to a bioavailability study with five different ciprofloxacin formulations.

Determination of the antidepressant fluoxetine in human plasma by LC with UV detection.

A selective and sensitive isocratic high-performance liquid chromatographic (HPLC) method was developed for the quantitative analysis of low concentrations of fluoxetine (FLX) in human plasma, with ultra-violet detection at 226 nm. A reversed-phase column, LiChrospher 60 RP-Select B (125 x 3 mm i.d., 5 microm) (Merck), was used to resolve FLX and diazepam (DZP) (internal standard) from endogenous matrix interferences. FLX was isolated from plasma by liquid-liquid extraction. Two identical HPLC systems were used, both validated under the same study conditions. Each chromatographic separation was completed in 30 min and the results showed a mean relative recovery of 101 and 99.3% and an overall precision (RSD%) of 4.78 and 6.09 for each HPLC system. The standard curve was linear for FLX concentrations over the range of 5.00-50.0 ng ml(-1) (R = 0.997 and 0.998). The limit of quantitation of FLX was 5 ng ml(-1) for both HPLC systems. The method described was applied to the analysis of plasma samples obtained from healthy subjects treated with one single oral dose of 40 mg of fluoxetine.

Comparative bioavailability of two immediate release tablets of cisapride in healthy volunteers.

Relative bioavailability of cisapride was investigated after oral administration of a test versus a reference formulation of immediate release tablets of cisapride, both with 10 mg per unit. The study was conducted in a two-way cross-over design, as a single dose open-label randomised trial. The two formulations were administered in two treatment days , separated by a washout period of 6 days, in fasted subjects who received one single oral dose of 20 mg of one study medication of cisapride as two 10 mg tablets. Multiple samples were collected over 24 h post-dosing. Plasma samples were assayed for cisapride using a selective and sensitive high-performance liquid chromatography (HPLC) method with UV detection. The pharmacokinetic parameter values (mean+/-RSD%) of cisapride as the test formulation were: AUC0-infinity=329+/-20.9 ng.h/ml, Cmax=52.8+/-22.6 ng/ml, tmax=1.26+/-22.0 h and t1/2=4.08+/-15 h. Following administration of the reference formulation the values obtained for the same parameters were: AUC0-infinity=317+/-19.2 ng.h/ml, Cmax=49.2+/-21.3 ng/ml, tmax=1.38+/-30.1 h and t1/2=4.52+/-24.8 h. These results show that the two cisapride formulations can be considered as bioequivalent, with respect to the above mentioned parameters.

Determination of apovincaminic acid in human plasma by high-performance liquid chromatography.

An isocratic high-performance liquid chromatographic method is described for the quantitative analysis of low concentrations of apovincaminic acid (AVA) in blood plasma. AVA, interfering plasma components and primidone (used as the internal standard) were separated on a reversed-phase column of LiChrospher 60 RP-Select B (125 mm x 3 mm i.d.; 5 microns) (Merck). A UV-Vis detector was used at a wavelength of 254 nm. Each chromatographic separation was completed in 14 min and the results showed a relative recovery which varied between 95.9 and 116%, a good overall precision (relative standard deviation, 7.00%) and sensitivity over a linear range of 5.00-300 ng ml-1 (R = 0.999) for AVA in plasma. The method was applied to the analysis of plasma samples obtained from healthy subjects treated with one single oral dose of 20 mg of vinpocetine. The results indicate the method to be suitable for pharmacokinetic studies.

A comparative bioavailability study to estimate the influence of an antacid on droxicam pharmacokinetics.

The influence of an antacid on droxicam pharmacokinetics was investigated in 12 healthy male volunteers. A two way cross-over study was performed after the oral administration of 20 mg of droxicam (Ombolan capsules) and droxicam together with an antacid (Mucal powder). The plasma concentrations of piroxicam, the active moiety of droxicam, were determined by a high-performance liquid chromatographic method. The pharmacokinetic parameter values (mean +/- RSD) of piroxicam after administration of droxicam alone were: AUC0-->infinity = 125.5 +/- 25.1 micrograms.h/l, Cmax = 2.08 +/- 19.9 micrograms/l, tmax = 7.08 +/- 36.8 h and t1/2 = 46.3 +/- 27.0 h. Following administration of droxicam together with the antacid the values obtained for the same parameters were: AUC0-->infinity = 135.1 +/- 24.1 micrograms.h/l. Cmax = 1.85 +/- 23.9 micrograms/l, tmax = 8.17 +/- 34.9 h and t1/2 = 52.0 +/- 22.4 h. These results indicate that concurrent administration of the antacid does not significantly change the bioavailability and pharmacokinetics of droxicam.

Sensitive method for the determination of phenytoin in plasma, and phenytoin and 5-(4-hydroxyphenyl)-5-phenylhydantoin in urine by high-performance liquid chromatography.

An isocratic high-performance liquid chromatographic method is described for the quantitative analysis of phenytoin (PHT) in plasma and both phenytoin and its main metabolite, 5-(4-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) in urine. Following ethyl acetate (plasma) and Extrelut-1 (urine) extraction, samples are analysed by means of a reversed-phase column (Nova-Pak C18), using a mobile phase consisting of methanol-water-tetrahydrofuran (40:60:4, v/v/v) with UV detection at 230 nm. The chromatography is complete in 10 min and the results show good precision (RSD 1.23-4.49%) and sensitivity for a linear range of 0.4-4.0 micrograms ml-1 for PHT in plasma, 0.1-1.0 microgram ml-1 for PHT in urine and 0.1-1.2 microgram ml-1 for p-HPPH in urine. The results indicate the method to be suitable for pharmacokinetic studies.

Application of non parametric methods to pharmacokinetic models of the Michaelis-Menten type.

Non linear parametric regression methods for data fitting as applied to complex pharmacokinetic models give rise to convergence difficulties which have not been completely solved. The Cornich-Bowden non parametric method was applied by Shelver to the one compartment open model with first order absorption to simulated data with different error structures. The application of his procedure was extended to a pharmacokinetic model with Michaelis-Menten elimination. Simulated concentration/time data were generated by a microcomputer program which imposed the appropriate error structure:constant and proportional standard deviation with or without one outlier of different magnitude. Parameter optimization was performed using either a Newton-Raphson algorithm based on the integrated form of the Michaelis-Menten equation and a standard non linear regression program: NONLIN. In the case of the non parametric method, the median of the parameter values obtained for each combination of data points was used as best estimate of the parameters. One hundred data sets were used and performance of the two methods was assessed by comparing bias and standard deviation of the mean parameter value thus obtained, given the true values of the parameters used to generate the data. The non parametric performed well with homoscedastic data and was less sensitive to the presence of outliers than the non linear regression technique. In the case of heterosocedastic data both methods performed poorly but the non parametric method was more sensitive to the presence of outliers.