LC method for therapeutic drug monitoring of levetiracetam: evaluation of the assay performance and validation of its application in the routine area.

OBJECTIVES: An accurate and precise high-performance liquid chromatographic method using diode array detection for the determination of levetiracetam in human plasma has been developed and validated for use in pharmacokinetic studies. METHODS: A harmonized validation strategy based on the accuracy profiles was used to select the most appropriate regression model and to determine the limits of quantitation as well as the concentration range of the developed analytical procedure. On the other hand, the present paper also shows this validation approach as a suitable tool to guaranty the quality of the results obtained by the use of the analytical validated methodology for plasma levetiracetam determination in a routine setting and to ensure the risk of obtaining the future measurements outside the previously fixed acceptance limits. RESULTS: As pointed recently, the FDA, a weighted 1/x(2) quadratic regression model ranging from 0.53 to 107.00 mg/L was selected as the simplest calibration model that maximized the accuracy all over the range. Relative bias was <5%, assay imprecision was always <6% and mean extraction recovery from plasma was >90%. So, accuracy did not exceed the acceptance limits settled at + or - 20% according to the FDA or Washington conference regulatory requirements for bioanalytical methods. Internal quality control has been assessed over a 2 year time period. All controls were essentially found to provide levetiracetam concentrations within the target range according to the FDA. CONCLUSIONS: The validated analytical procedure complies with strongest regulatory standards. The validated method has a sufficiently rapid turnaround time and their results are good enough to enable the laboratory to routinely provide useful and accurate pharmacokinetic data in time to adjust patient regimens.

Phase I and pharmacokinetic study of gemcitabine administered at fixed-dose rate, combined with docetaxel/melphalan/carboplatin, with autologous hematopoietic progenitor-cell support, in patients with advanced refractory tumors.

The purpose of this trial was to define the maximum tolerated duration (MTD), dose-limiting toxicity (DLT), regimen-related toxicities (RRT), and pharmacokinetics of gemcitabine infused at a fixed dose rate (FDR) of 10 mg/m2/min, combined with docetaxel/melphalan/carboplatin, using autologous stem cell transplantation (ASCT). The duration of gemcitabine infusion was incrementally escalated as a single treatment on day -6 or as 4 daily infusions on days -5 to -2. Gemcitabine was followed by docetaxel (300 or 350 mg/m2) on day -5, and then melphalan (50 mg/m2/day) and carboplatin (333 mg/m2/day) on days -4 to -2. Fifty-two patients with refractory tumors were accrued with a median age of 40 (range: 6-66), a median of 3 (1-6) prior chemotherapy regimens, and 3 (1-7) organs involved. The gemcitabine MTD was defined at 20 hours (total dose 12,000 mg/m2) on both schedules. The DLT was enteritis. Three patients died from aspiration, catheter-related sepsis, and enteritis, respectively. The tumor response rate was 91%, with 50% complete responses. At current 2-year median follow-up, the event-free and overall survival (EFS, OS) rates are 54% (median 26 months) and 79% (median not reached), respectively. Gemcitabine area under the curve (AUC), but not clearance, increased linearly with infusion duration, and correlated with grade 3 RRT. Docetaxel showed a linear increase of its AUC and similar clearance compared with prior reports at lower doses. In conclusion, ASCT-supported infusions of gemcitabine at FDR could be prolonged up to 20 hours. The resulting gemcitabine/docetaxel/melphalan/carboplatin combination was highly active in refractory cancers and should be further tested in disease-specific trials.

Determination of 5-fluorouracil and its prodrug tegafur in plasma and tissue by high-performance liquid chromatography in a single injection: validation for application in clinical pharmacokinetic studies.

Tegafur, a prodrug of 5-fluorouracil (5-FU), is an oral fluorouracil antitumor drug used for the management of adenocarcinomas. It has an efficacy similar to that of intravenous 5-FU, with potential advantages in terms of convenience and quality of life for the patient and cost-effectiveness as compared with intravenous chemotherapy. The authors developed a high-performance liquid chromatography (HPLC) assay for the determination of tissue or plasma tegafur and 5-FU concentration in a single step extraction and a single HPLC injection. The retention times of 5-FU and tegafur were 5 and 16.5 minutes, respectively, and the internal standard retention times were 11.5 and 17.5 minutes for 5-bromouracil (5-BU) and beta-hydroxyethyltheophylline, respectively. The limit of quantification was 0.0125 microg/mL for 5-FU and 0.05 microg/mL for tegafur. The assay had good recovery (96.5% +/- 9.45% and 97.5% +/- 7.89% for 5-FU in plasma and tissue, respectively, and 88.5% +/- 12.17% and 104.9% +/- 8.77% for tegafur in plasma and tissue, respectively). Precision was good: the within-day and between-day standard deviation of the mean (RSD) for 5-FU (0.0125-5 microg/mL) and tegafur (0.5-150 microg/mL) was always <8%. The authors conclude that the method described here is ideally suited for the therapeutic monitoring of 5-FU and tegafur.