On-line fully automated solid-phase extraction-liquid chromatography analysis of 1,2-dihydro-4-(1,2-dihydro-2-oxo-1-pyridyl)-2,2-dimethyl-1-oxonaphthale ne-6- carbonitrile (UR-8225), a new potassium channel opener, in plasma samples

A fully automated reversed-phase HPLC method for pharmacokinetic studies was developed for the determination in plasma samples of 1,2-dihydro-4-(1,2-dihydro-2-oxo-1-pyridyl)-2,2-dimethyl-1-oxonaphtha lene-6- carbonitrile (compound I), a new potassium channel opener. On-line solid-phase extraction was performed with disposable C18 cartridges. After clean up, the samples were eluted and transferred onto an RP-18 analytical column, where separation was performed with a mobile phase of acetonitrile-10 mM di-n-butylamine phosphate (28:72, v/v). Ultraviolet absorbance detection was used at 236 nm. The detector response was linear in the range 25-2500 ng/ml, and the lowest limit of quantitation was determined at 2.5 ng/ml. The inter-day variability was < 4% for samples at 1000 ng/ml and < 15% for samples at 10 ng/ml. This method was used for the pharmacokinetic study of compound I in rats at three different dosage levels.

An automated analytical method for the determination of felbamate in human plasma by robotic sample preparation and reversed-phase high performance liquid chromatography

An automated analytical method for the determination of felbamate in human plasma is described. Sample cleanup and preparation was performed by means of a Zymate II laboratory robot and consisted of a liquid-liquid extraction of felbamate and the internal standard, primidone, from human plasma to dichloromethane. The dichloromethane was evaporated and reconstituted in a phosphate buffer. Separation was performed by reversed-phase high performance liquid chromatography using a 5 microns Hypersil ODS column (150 x 4.6 mm) and a mobile phase consisting of a mixture of phosphate buffer (pH = 6.5, 0.015 M) and acetonitrile (79:21, v/v). Quantitation was performed by measurement of the UV absorbance at a wavelength of 210 nm. The lower limit of quantitation was 0.100 micrograms ml-1 using 200 microliters of plasma. The mean absolute analytical recovery of felbamate was 75.2% (n = 28). The recovery of the internal standard, primidone was 74.7% (n = 10). The within-day precision was below 3.8% at all concentration levels, except at the lower limit of quantitation (18.3%). The within-day accuracy varied between -3.7 and +7.4%. The between-day precision was below 5.0% at all concentration levels. The between-day accuracy of the method varied between -5.7 and +1.6%. The selectivity of the method towards several other anti-epileptic drugs has been demonstrated.

Determination of alpha-tocopherol in plasma and erythrocytes by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method for the determination of alpha-tocopherol in plasma or erythrocytes with photodiode-array detection is described. Using this detector, information about the spectrum, absorption maxima and purity of the peak is obtained. Tocopherol was separated on a 5-microns Spherisorb ODS-2 column with methanol as element at a flow-rate of 1.0 ml/min. As little as 100 microliters of plasma or 150 microliters of erythrocytes can be used for accurate analysis with direct extraction without saponification. The speed, specificity, sensitivity and reproducibility of this technique make it particularly suitable for the routine determination of alpha-tocopherol in plasma or erythrocytes.

Paired ion reversed-phase HPLC assay for the determination of iothalamic acid and para aminohippuric acid in urine

A paired ion reversed-phase high performance liquid chromatographic method for simultaneous determination of iothalamic acid (Io) and para aminohippuric acid (PAH) in urine is described. The method uses a single internal standard for both drugs. The only sample preparation required is dilution of urine (1:100 or 1:500) with deionized water. The internal standard is added to a small aliquot of the diluted specimen and injected. For HPLC, a C8 column and a mobile phase consisting of potassium phosphate buffer with dodecyl triethylammonium phosphate IP reagent, 25% organic modifier with UV detection at 254 nm was used. Within day and between day variation for the assay were in the range of 1.48-9.46% for iothalamic acid and 1.84-10.36% for para aminohippuric acid for four levels of concentration. Limits of quantitation were 50.0 micrograms ml-1 for iothalamic acid and 75.0 micrograms ml-1 for para aminohippuric acid. Mean recovery was 98.55% for Io and 97.79% for PAH. This isocratic HPLC assay is simple, rapid and relatively inexpensive.

Quantitative measurement of BN50727 in human plasma and urine by combined liquid chromatography/negative ion chemical ionization mass spectrometry using a particle beam interface

A new sensitive assay has been developed for the quantitative measurement of BN50727 at the picomole level in human plasma and urine. The drug and the internal standard (BN50788) were measured by combined liquid chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. A simple solid-liquid extraction procedure was used to isolate BN50727 from the complex biological matrices. The mass spectrometer was tuned to monitor the intense and stable ion at m/z 333 which was generated in the ion source by a dissociative capture process. This assay was performed with 1 ml of plasma or 0.1 ml of urine and the quantification limit of the method was statistically calculated as 1 ng ml-1. The very low relative standard deviations and mean percentages of error calculated during the different within-day or between-day repeatability assays have clearly demonstrated the ruggedness of the technique for the routine determination of BN50727 in biological fluids. Some preliminary results on the pharmacokinetics of the drug are presented to illustrate the applicability of this powerful liquid chromatographic/mass spectrometric method.

Multiple-dose pharmacokinetics of ceftibuten after oral administration to healthy volunteers

The pharmacokinetics of ceftibuten in plasma and urine were investigated after oral administration. Twelve healthy subjects were treated orally twice daily with 400 mg of the drug for 7 days; on day 8, the subjects received a last dose of 400 mg of ceftibuten. Ceftibuten and its metabolite, the trans isomer of ceftibuten, were assayed in plasma and urine by a specific HPLC method with UV detection. Ceftibuten was rapidly absorbed, as evidenced by the mean time to the maximum observed cis-ceftibuten concentration of 2.4 h. To describe the drug intake process, a Weibull model was used. For the metabolite, the mean time to maximum concentration in plasma was 3.25 h. Mean values for the terminal half-life in plasma were 2.17 h for cis-ceftibuten and 3.19 h for trans-ceftibuten. The overall elimination half-life, tmax, and total and renal clearances of cis-ceftibuten were invariant with respect to duration of dosing. The area under the plasma concentration versus time curve from 0 to infinity and the Cmax of this drug were significantly higher on day 8 than the values predicted from the elimination half-life computed on day 1 of treatment and the dosing interval. The pharmacokinetic parameters of trans-ceftibuten were invariant with respect to duration of dosing. Ceftibuten was well tolerated; there were no clinically significant adverse clinical events. The results from the present study indicate that the levels of cis-ceftibuten in plasma as well as in urine remain above the MICs for susceptible organisms over the dosing interval.

Quantitative measurement of zacopride in human plasma and urine by combined gas chromatography/negative ion chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for routine analysis of zacopride at the femtomole level in human plasma and urine. Zacopride and the deuterated internal standard [(2H3)zacopride] were measured by gas chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. A multiple-step liquid-liquid extraction procedure was used to isolate the two compounds of interest from complex biological matrices. Zacopride was converted to the fluorinated derivative with pentafluoropropionic anhydride. The mass spectrometer was tuned to monitor the very intense [M-HF]- ion at m/z 435 which was generated into the ion source by a dissociative capture process. This assay was performed with 1 ml of plasma or 0.2 ml of urine, and the quantification limit of the method was calculated as 10 pg ml-1 using a suitable statistical test. The very low relative standard deviation and mean percentage error values calculated during the within-day or between-day repeatability assays have clearly demonstrated the ruggedness of the technique for the routine quantitative measurement of zacopride in plasma and urine. Some preliminary results on the pharmacokinetics of this potent drug are presented to illustrate the applicability of this new powerful gas chromatographic/mass spectrometric method.

Quantitative measurement of a new synthetic hetrazepine derivative, BN50730, in human plasma and urine by combined liquid chromatography-negative chemical ionization mass spectrometry using a particle beam interface

A new simple and sensitive assay has been developed for the quantitative measurement of BN50730 at the picomole level in human plasma and urine. The drug and the internal standard (BN50765) were measured by combined liquid chromatography-negative chemical ionization mass spectrometry with methane as the reagent gas. A simple solid-liquid extraction procedure was used to isolate BN50730 from complex biological matrices. Mild operating conditions were required to assay the parent drug with a particle beam interface from Hewlett-Packard. The mass spectrometer was tuned to monitor the intense ion m/z 333, which was generated in the ion source by a dissociative capture process. This assay was performed with 1 ml of plasma or 0.1 ml of urine, and the quantification limit of the method was statistically calculated as 1 ng ml-1. The very low relative standard deviation and mean percentage of error calculated during the different within-day or between-day repeatability assays clearly demonstrate the ruggedness of the technique for the routine determination of BN50730 in the biological fluids. Some preliminary results on the pharmacokinetics of the drug are presented to illustrate the applicability of this new powerful LC-MS method.

The influence of food on the disposition of the antiepileptic oxcarbazepine and its major metabolites in healthy volunteers

The effect of food on the pharmacokinetics of the antiepileptic oxcarbazepine (OXC) was investigated in healthy volunteers. Six healthy male volunteers were treated with single peroral doses of 600 mg of oxcarbazepine (Trileptal) after overnight fasting or a fat- and protein-rich breakfast. Mean (+/- SD) areas under the plasma concentration-time curves (AUC) of the major component in plasma, the active monohydroxy metabolite (MHD), which is responsible for the therapeutic effect in man, were 672 (25) mumol L-1 h when given to the fasted volunteers and 780 (31) mumol L-1 h (p = 0.042) when given after a substantial breakfast. Mean (+/- SD) maximum concentrations (Cmax) were 25.5 (4.8) mumol L-1 when given to the fasted volunteers and 31.4 (5.3) mumol L-1 (p = 0.025) when given after breakfast. Thus, the average AUC was increased by 16% and Cmax by 23% when oxcarbazepine was given with food. The times at which Cmax was reached (tmax) as well as the terminal half-lives were not influenced by concomitant intake of food. The tolerability was the same whether oxcarbazepine was given before or after food in healthy volunteers. The slight effect of food on the kinetics of oxcarbazepine should be of little therapeutic consequence.

A highly sensitive assay of melatonin at the femotogram level in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry

A highly sensitive and specific assay was developed for routine analysis of melatonin at the femotogram level in human plasma. Melatonin and the deuterated internal standard [(2H4)melatonin] were measured by gas chromatography/negative ion chemical ionization mass spectrometry with methane as the reagent gas. A simple liquid-liquid extraction procedure was used to isolate the two compounds of interest from the complex biological matrix. Melatonin was converted to the fluorinated derivative with pentafluoropropionic anhydride. The mass spectrometer was tuned to monitor the very intense and stable ions at m/z 320 and 323 which were generated into the ion source by a dissociative capture process. This assay was conducted with 1 ml of plasma and the quantification limit of the method was statistically calculated as 0.5 pg ml-1. The very low relative standard deviations and mean percentages of error calculated during the within-day or between-day repeatability assays have clearly demonstrated the ruggedness of the technique for the routine quantitative measurement of melatonin in plasma. Some results on the melatonin circadian rhythm are presented to illustrate the applicability of this powerful gas chromatographic/mass spectrometric method.

Quantitative determination of CGP 53,437, a new HIV protease inhibitor, in plasma by high-performance liquid chromatography and fluorescence detection

A specific and sensitive liquid chromatographic assay for CGP 53,437 (I), a potent HIV protease inhibitor, is described. The method is based on a deproteinization step, followed by a liquid-liquid extraction with diisopropyl ether. Then a deprotection step of the primary amine and derivatization using fluorescamine is performed. Chromatography is achieved by isocratic elution with a mobile phase of 63 mM borax buffer (pH 9)-acetonitrile (58:42, v/v). The flow-rate of the mobile phase is 1 ml/min. The derivatives of compound I and its internal standard CGP 54,451, II, fluoresce at 480 nm on excitation at 395 nm. The limit of quantitation which is the lowest concentration of the analyte that can be measured with a coefficient of variation and a deviation from theory of less than 20%, was 5 nmol/l plasma. The analyte is stable for at least seven months in spiked human plasma samples. It is also stable after freezing and thawing cycles. Different human plasma sources and plasma samples from three different species (dog, marmoset, and rat) were tested and no interferences from plasma constituents was observed.

Development and validation of an LC method for the quantitation of carbenicillin in human serum

An LC method for the quantitation of carbenicillin in human serum has been developed and validated. After protein precipitation with acetonitrile and evaporation, the residue was taken up by citric acid at pH 1.9. Carbenicillin and the internal standard (I.S.), piperacillin, were extracted with ethyl acetate, evaporated to dryness and reconstituted with a buffer solution. The separation of carbenicillin,, the I.S., and matrix peaks was achieved on a Microsorb C18, 3 microns column with a mobile phase of acetonitrile-tetrabutylammonium-phosphate buffer (pH* 6.6). The detection was by UV at 208 nm. The run time was 8 min. The established linearity range was 0.25-20 microgram ml-1 (r2 > 0.99) with a limit of quantitation of 0.25 microgram ml-1. Interday precision (RSD) and bias over the entire range were 1.1-6.9% and -1.83 to +2.80%, respectively. The interday precision (RSD) and bias for the QC samples at 0.75, 3.0 and 12 micrograms ml-1 were 5.9-7.9% and -2.80 to +2.30%, respectively. Stabilities of on-system, bench top, freeze-thaw cycles and sample storage were established.

High-performance liquid chromatographic determination of ceftibuten and its metabolite in biological fluids: applications in pharmacokinetic studies

An HPLC method with UV detection was developed for the analysis of ceftibuten (cis-isomer) and its metabolite (trans-isomer of ceftibuten) in plasma and urine. The detection was performed at 254 nm. The procedure for the plasma assay involves the addition of an internal standard (ceftazidime), followed by treatment of the samples with acetonitrile and dichloromethane. The urine samples, after dilution (10- to 40-fold), were analyzed by a column-switching technique without internal standard. The proposed technique is reproducible, selective, reliable, and sensitive. Linear detector responses were observed for the calibration curve standards in the ceftibuten conentration range of 0.10 to 20 mg/L for plasma and 0.10 to 50 mg/L for urine, and in the metabolite concentration range of 0.20 to 4 mg/L for plasma and 0.20 to 16 mg/L for urine. The limit of quantitation is 0.1 mg/L for ceftibuten and 0.2 mg/L for the transisomer in plasma and urine. The reproducibility of the analytical method according to the statistical coefficients is approximately 7%. The accuracy of the method is good; that is, the relative error is < 5%. The methods were applied to pharmacokinetic studies of ceftibuten after multiple oral administration (400 mg every 12 h for 8 days) to healthy volunteers.

Pharmacokinetics of rec-hirudin in healthy volunteers after intravenous administration

The pharmacokinetics of recombinant hirudin (rec-hirudin, Ciba-Geigy, CGP 39,393) in healthy volunteers after iv administration was investigated on the basis of the data from five different studies. A total of 77 plasma profiles following a single iv bolus dose of either 0.1, 0.3, 0.5, or 1 mg/kg of rec-hirudin was used for the evaluation. Plasma concentrations and especially AUC were proportional to the dose. Kinetics of rec-hirudin after a bolus iv injection were best described by a three-compartment open model. Mean apparent terminal half-life was 2.8 hr and the total clearance 0.138 L/hr per kg.

Development, application and comparison of an enzyme immunoassay and a high-performance liquid chromatography method for the determination of the aromatase inhibitor CGS 20,267 in biological fluids

CGS 20,267 is a new potent and selective, nonsteroidal, oral aromatase inhibitor. For its determination in human plasma and urine, an enzyme immunoassay (EIA) and an HPLC method were developed. The EIA showed good precision and accuracy (intra- and interassay variation between 3.0 and 17.7%, recoveries between 81 and 106%) and a quantitation limit of 0.7 nmol/L. A strong cross reactivity of the antibodies with the hydroxy metabolite of CGS 20,267 (CGP 44,645) was observed. The HPLC method showed a quantitation limit in plasma of 28 and 34 nmol/L for CGS 20,267 and CGP 44,645, respectively. For urine, concentrations down to 180 nmol/L (CGS 20,267) and 210 nmol/L (CGP 44,645) could be measured. A cross check between EIA and HPLC on plasma samples from healthy male volunteers or breast cancer patients treated orally with CGS 20,267 revealed an excellent correlation (slope = 0.934, intercept = 26, r = 0.991). However, the EIA measurements of urine samples yielded 3-25 times higher concentrations than those obtained by HPLC. Further, HPLC analysis revealed the presence of CGS 20,267 and cross-reacting metabolites in urine but not in plasma. Therefore, the EIA can only be used for the determination of CGS 20,267 in plasma samples.

Development and validation of a liquid chromatographic method for the quantitation of ibuprofen enantiomers in human plasma

A method for the quantitation of ibuprofen enantiomers in human plasma has been developed and validated. Separation of R- and S-ibuprofen was achieved on a silica-bonded beta-cyclodextrin column with a mobile phase of acetonitrile-0.02% (v/v) triethylamine in water adjusted to pH 4.0 with glacial acetic acid in water (60:40, v/v). The UV detection was performed at 220 nm. The established linearity range was 1-25 micrograms ml-1 (r > 0.99). The limit of quantitation was designed as 1 microgram ml-1 for each enantiomer. Interday precision and accuracy for the standards were 2.2-5.9% relative standard deviation (RSD) and -2.9(-)+3.5% relative error for R-ibuprofen, and 1.9-6.3% RSD and -7.1(-)+4.4% relative error for S-ibuprofen. Interday precision and accuracy for quality controls at 2.5, 7.5 and 17.5 micrograms ml-1 were 6.1-6.4% RSD and -1.4(-)+0.8% relative error for R-ibuprofen, and 5.7-5.9% RSD and -1.2(-)+2.8% relative error for S-ibuprofen. p-Isopropylbenzoic acid was used as an internal standard. The run time was 26 min. Interference from various lots of human plasma were not observed. Stability results of on-system, re-injection, bench-top, freeze-thaw cycles and sample storage were established.

Simultaneous determination of dihydrocodeine and its metabolites in dog plasma by high-performance liquid chromatography with electrochemical and ultraviolet detection

An HPLC method with electrochemical and UV detection was established for the simultaneous determination of dihydrocodeine and its metabolites, dihydronorcodeine, dihydromorphine, and dihydrocodeine glucuronide, in dog plasma using N-ethylnormorphine as the internal standard. The method involved sample pretreatment with a C18-bonded disposable column, and the injected fraction was separated and detected on the C18-bonded column with serially coupled UV and coulometric detectors. Dihydromorphine was detected with the coulometric detector at 0.4 V, and dihydrocodeine and dihydronorcodeine at 0.8 V. Dihydrocodeine glucuronide was detected with UV at 210 nm. Recoveries of the studied compounds were quantitative at the individual assay ranges, and validation of the assay gave results that were satisfactory in terms of within-run or between-run precision and accuracy. Lower limits of quantitation were 2 ng/ml for dihydrocodeine and dihydronorcodeine, 0.5 ng/ml for dihydromorphine, and 200 ng/ml for dihydrocodeine glucuronide.

Determination of L-2-oxothiazolidine-4-carboxylic acid (Procysteine) in human plasma by high-performance liquid chromatography

A new high-performance liquid chromatographic (HPLC) method has been developed for the determination of the cysteine prodrug, L-2-oxothiazolidine-4-carboxylic acid (Procysteine), in human plasma. Samples were mixed with 5% metaphosphoric acid and the supernatants chromatographed using a reversed-phase analytical column. Procysteine was detected spectrophotometrically at 230 nm and quantitated by comparison with a standard curve of known amounts of Procysteine (20-1000 microM) in plasma. The coefficients of variation for 48.6 microM and 676 microM control pools were 6.5 and 4.0% respectively (n = 46). Deviations from the expected concentrations were less than 2%. The method has been utilized to evaluate the pharmacokinetics of a wide range of oral and intravenous doses.

Development and validation of a high-performance liquid chromatographic method for the determination of methocarbamol in human plasma

An isocratic HPLC method was developed and validated for the quantitation of methocarbamol in human plasma. Methocarbamol and internal standard in 200 microliters of human plasma were extracted with ethyl acetate, evaporated to dryness and reconstituted in water. Separation was achieved on a reversed-phase C18 column with a mobile phase of methanol-0.1 M potassium phosphate monobasic-water (35:10:55, v/v/v). The detection was by ultraviolet at 272 nm. Linearity was established at 1-100 micrograms/ml (r > 0.999). The limit of quantitation was designed as 1 microgram/ml to suit pharmacokinetic studies. Inter-day precision and accuracy of the calibration standards were 1.0 to 3.6% coefficients of variance (C.V.) and -2.0 to +1.6% relative error (R.E.). Quality controls of 3, 20 and 70 micrograms/ml showed inter-day precision and accuracy of 2.5 to 3.6% C.V. and -0.9 to -0.4% R.E. Recovery of methocarbamol was 91.4-100.3% in five different lots of plasma. The method was shown to be applicable on different brands of C18 columns.

Sample clean-up and high-performance liquid chromatographic techniques for measurement of whole blood rapamycin concentrations

Determination of rapamycin (RAPA), a potential adjunct to cyclosporin immunosuppressive therapy in solid organ transplantation, presents a challenge because of the agent's unusual chemical properties. RAPA is not readily extracted from biological matrices, is light-sensitive, and exists in numerous isomeric forms. Using liquid-liquid extraction techniques with tert.-butyl methyl ether followed by ethanol, one achieves 96% recovery of RAPA and 70% recovery of the internal standard, beta-estradiol-3-methyl ether, from human whole blood. Subsequent high-performance liquid chromatography (HPLC) utilizing two heated reversed-phase C18 columns in tandem and an 85% methanol-water mobile phase with ultraviolet detection at 276 nm provides measurement of RAPA from 1-ml samples of human whole blood. The chromatography requires less than 40 min per sample. The assay exhibits < or = 10% standard error of the mean and < or = 12% coefficient of variation over the concentration range 2-100 ng/ml. The method has been tested using pharmacokinetic profiles from renal transplant recipients receiving bolus intravenous RAPA infusions.

Accuracy and precision for analytical results

Unknown amounts of drug from plasma samples are determined from inverse prediction of a calibration line. A statistician's criteria for accuracy and three methods for computing precision are given.

High-performance liquid chromatographic assay for the measurement of atovaquone in plasma

A rapid and efficient isocratic high-performance liquid chromatographic assay for the measurement of atovaquone in plasma has been developed and validated. The drug was extracted from plasma with organic solvents, assayed on a C1 column with a mobile phase of methanol-0.1% acetic acid (70:30, v/v), and detected by ultraviolet absorbance at 254 nm. Recovery of atovaquone from plasma was greater than 85%. Intra- and inter-assay variability were less than 8%, and the average accuracy of the assay (expressed as % bias) ranged from -7.4 to + 2.2%. The upper and lower limits of quantitation were 100 and 0.25 microgram/ml, respectively. Measurement of atovaquone in spiked plasma control samples during routine runs of clinical trial samples confirmed the reliability of the assay.

Sensitive procedure for the determination of reboxetine enantiomers in human plasma by reversed-phase high-performance liquid chromatography with fluorimetric detection after chiral derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate

A sensitive and selective high-performance liquid chromatographic method for the determination of reboxetine enantiomers in human plasma was developed. Although two chiral centres are present in reboxetine, its stereospecific synthesis leads to two rather than four possible enantiomers. After extraction from plasma and reaction with (+)-1-(9-fluorenyl)ethyl chloroformate, reboxetine enantiomers were separated as diastereoisomeric derivatives by reversed-phase high-performance liquid chromatography (HPLC) and determined by fluorimetric detection. The HPLC analysis time was about 90 min. The linearity, precision, accuracy and limit of quantification of the method were evaluated. No interference from blank plasma sample was observed. The suitability of the method for in vivo samples was assessed by the analysis of plasma samples obtained from a healthy male volunteer who had received a single oral dose of 4 mg of reboxetine in tablet form.

High-performance liquid chromatographic determination of m-iodobenzylguanidine in urine of cancer patients

An accurate, sensitive, reproducible and selective HPLC assay is presented for the quantitative determination of m-iodobenzylguanidine (MIBG) in human urine. The sample pretreatment involves a solid-phase extraction on Bakerbond SPE cyano columns. The HPLC systems consists of a muBondapak C18 column and 25 mM ammonium phosphate (pH 3.0)-acetonitrile (75:25, v/v) as the mobile phase. Detection is performed by UV absorbance at 254 nm. Log y vs. log x is the response function that yielded the smallest sum of percent relative concentration residuals over the whole concentration range of the assay (0.2-100 micrograms/ml). The excretion profile of MIBG in urine of a three-year old patient is shown.

Comparative pharmacokinetics and pharmacodynamics of two marketed bid formulations of diltiazem in healthy volunteers

Cardizem SR and Bi-Tildiem were both approved in their respective countries on the basis of clinical trials demonstrating efficacy and safety in the treatment of angina pectoris. In this cross-over randomized study, we assessed whether these two sustained-release formulations of diltiazem have equivalent pharmacokinetic and pharmacodynamic profiles. Twenty-four young healthy male volunteers were hooked to Holters and ambulatory blood pressure monitors for 24 h to establish baseline systolic blood pressure (SBP), diastolic blood pressure (DBP), sinus rate and PR intervals. They then received a single dose of 120 mg of diltiazem from one formulation. The pharmacodynamic measurements were recorded for a further 24 h and blood samples were collected over 36 h for evaluation of diltiazem in plasma by a high-performance liquid chromatogrpahic (HPLC) method. The procedures were repeated with the alternate formulation after a 7 d wash-out. Pharmacokinetics showed statistically significant (p < 0.01) differences in AUC0-12 with means (+/- SD) of 519.2(+/- 172.8) and 429.6(+/- 147.2) ng h ml-1, AUC0-36 of 835.6(+/- 281.6) and 730.9 (+/- 271.5) ng h ml-1 and Cmax of 89.1(+/- 30.3) and 61.1(+/- 21.2) ng ml-1 for Cardizem SR and Bi-Tildiem, respectively. The only pharmacodynamic parameter showing a statistically significant difference in change from baseline between the two formulations was DBP with mean (+/- SD) change in AUC0-12 of -13.6(+/- 20.8) and +8.4(+/- 31.7) mm Hg h (p = 0.0135) and in AUC0-24 of -33.0(+/- 43.7) and -0.3(+/- 59.2) mm Hg h (p = 0.0463) for Cardizem SR and Bi-Tildiem, respectively. These findings suggest that assessment of efficacy of sustained-release formulations of diltiazem by bioequivalence could be misleading. They also confirm that a single dose of diltiazem does not elicit a significant pharmacodynamic response in healthy volunteers. Equivalence for such formulations should therefore be demonstrated by pharmacodynamic evaluation or clinical studies in a patient population.

Evaluation of the bioequivalence of tablet and capsule formulations of granisetron in patients undergoing cytotoxic chemotherapy for malignant disease

Granisetron is a novel, highly specific 5-hydroxytryptamine receptor antagonist given prophylactically to patients undergoing chemotherapy. An open, randomized, crossover trial was performed with 37 patients (24 females and 13 males) undergoing cytotoxic chemotherapy for malignant disease to compare an oral tablet (1-mg tablet given twice daily) with a clinical-trial capsule (1-mg capsule given twice daily). Complete pharmacokinetic data were determined for 24 patients (14 females and 10 males). The concentration of granisetron in plasma was measured by HPLC; the limit of quantitation was 0.2 ng/mL. The bioavailability evaluation was based mainly on the area under the curve (AUC) (mean values: 52.1 ng.h/mL for the capsule and 54.2 ng.h/mL for the tablet) and the maximum concentration (Cmax) (mean values: 7.42 ng/mL for the capsule and 8.18 ng/mL for the tablet) measured at the steady state after 7 days of continuous therapy. Wide interpatient variability in plasma granisetron levels after oral administration was observed. The 90% standard confidence interval for the geometric mean ratio overlapped the critical range, 0.8-1.25. Point estimates for AUC and Cmax based on two one-sided t tests and log-transformed data showed that the upper limit of the confidence interval was not within 20% of the mean for the capsule; the corresponding power analysis values for AUC and Cmax were 0.89 and 0.81, respectively. Despite bioequivalence not being proven, any differences that exist between the two formulations are likely to be small. There was no difference in efficacy or safety between the two formulations assessed.

Development and validation of a high-performance liquid chromatographic method for the quantitation of warfarin enantiomers in human plasma

An HPLC method for the quantitation of warfarin enantiomers in human plasma has been developed and validated. Baseline separation of S- and R-warfarin was achieved on a silica-bonded beta-cyclodextrin column with a mobile phase of acetonitrile-acetic acid-triethylamine (1000:3:2.5, v/v/v). The detection was performed at 320 nm. The established linearity range was 12.5-2500 ng ml-1 (r > 0.99). The limit of quantitation was 12.5 ng ml-1 for each enantiomer. Inter-day precision and accuracy of 12.5 ng ml-1 standards were 12.1% relative standard deviation (RSD) and +0.67% bias for S-warfarin and 9.7% RSD and +10.8% bias for R-warfarin. The low quality control samples at 37.5 ng ml-1 showed 6.9% RSD and 0.0% bias for S-warfarin, 7.2% RSD and +0.5% bias for R-warfarin. S-Naproxen was used as internal standard. Potential metabolites of warfarin were well resolved from S- and R-warfarin, the internal standard (S-naproxen) and each other. The run time was 25 min. The silica-bonded beta-cyclodextrin column showed excellent stability; over 1000 samples were injected without significant loss of performance. The column variability test showed that the method can be applied on several batches of beta-cyclodextrin columns but not all the beta-cyclodextrin columns were suitable for this method.

Application of solid-phase extraction in the determination of U-82217 in rat serum, urine and brain

The techniques of solid-phase extraction (SPE) were applied in the analytical method development for the determination of U-82217, 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-5-[(4-methoxyphenyl)methyl] -imidazo[1,5-a]quinoxalin-4(5H)-one, in rat serum, urine and brain. Samples of serum, urine or brain homogenate containing U-82217 were loaded on C18 SPE columns and eluted with acetonitrile (300 microliters). The prepared samples were analyzed by reversed-phase HPLC using an ODS column with a mobile phase of acetonitrile-water (45:55, v/v) containing 0.12% of acetic acid (pH 6.0 +/- 0.1). The UV absorbance of the column effluent was monitored at a wavelength of 318 nm. The absolute extraction recovery from serum, urine and brain samples was ca. 90%. Linear calibration graphs were obtained over the ranges 5 ng/ml-20 micrograms/ml (serum), 20 ng/ml-20 micrograms/ml (urine) and 50 ng/g-200 micrograms/g (brain). The intra- and inter-assay precision and accuracy were all found to be < 13% at the concentrations evaluated. The strategy in SPE development and the application of this method to the determination of U-82217 in rat serum and brain for a pharmacokinetic study are also discussed.

Stereoselective determination of the enantiomers of methadone in plasma using high-performance liquid chromatography

An enantioselective high-performance liquid chromatographic assay for the quantification of methadone in human and beagle plasma is described. The procedure involves extraction of methadone from alkalized plasma into hexane-isoamyl alcohol (99:1, v/v). Stereoselective separation was achieved with a silica column with covalently bound alpha 1-acid glycoprotein (Chiral-AGP) without any derivatization procedure. The detection wavelength was set at 215 nm. Using an internal standard provided reliable control of the extraction procedure as well as quantification of the enantiomers of methadone. The limit of quantification was found to be 2.5 ng/ml. The method was demonstrated to be sufficiently sensitive for stereoselective pharmacokinetic studies of methadone.