Simple HPLC Method for Quantitative Determination of Carbinoxamine in Human Plasma: Application in Pharmacokinetic Studies and Therapeutic Drug Monitoring.

A sensitive, specific and cost-effective HPLC method was developed for quantitative determination of carbinoxamine in human plasma using liquid chromatography with ultraviolet detection. A simple liquid-liquid extraction by ethyl acetate was used to extract carbinoxamine from human plasma. Satisfactory separation was achieved by a mobile phase consisting of 20 mM ammonium dihydrogen orthophosphate containing 0.01% triethyl amine (pH adjusted to 3 by using phosphoric acid) and acetonitrile in ratio of (75:25, v/v) at a flow rate of 0.9 mL/min on Hypersil® BDS C18 column (250×4.6 mm, 5 µm) column. The UV detector was set at 260 nm. The developed method was validated in human plasma with a lower limit of quantitation of 5 ng/mL for carbinoxamine. Linearity was demonstrated over the concentration range 5-200 ng/mL. The observed within- and between-day assay precision ranged from 1.902 to 14.90%; accuracy varied between 98.87 and 108.0%. This method can be used suitably for pharmacokinetic studies and in therapeutic drug monitoring in patients treated with carbinoxamine.

An assessment of the impact of green tea extract on palbociclib pharmacokinetics using a validated UHPLC-QTOF-MS method.

Green tea extracts (GTE) has been reported to be a kinase inhibitor and modulator for various drug metabolizing enzymes. It may give synergetic antioncogenic effect, but with a possibility of pharmacokinetic interactions with various co-administered anticancer agents like palbociclib (PAL), a selective inhibitor of CDK-4/6 primarily metabolized by CYP3A enzyme. To explore the impact of GTE on PAL pharmacokinetics in Sprague-Dawley rats, a rapid and sensitive UHPLC-QTOF-MS method was established. Chromatographic separation was carried out on an Acquity UPLC BEH C18 (100 × 2.1 mm, 1.7 µm) column using a gradient mobile phase system consisting of 0.1% formic acid and acetonitrile. Sample preparation was based on a simple protein precipitation method. Estimation of target ions [M + H]+ at m/z 448.2455 for PAL and m/z 441.2044 for ibrutinib (IS) was performed in selective ion mode ESI-HRMS. Good sensitivity (1.0 ng/mL) and linearity over a wide concentration range of 1-2000 ng/mL was exhibited by the method. The results indicated that the administration of GTE resulted in decreased oral bioavailability of PAL in both short- and long-term conditions. However, when both conditions were compared, the variation was less for the peak concentration and area under the concentration-time curve level of PAL.

Pharmacokinetic/Pharmacodynamic Analysis of Isavuconazole Against Aspergillus spp. and Candida spp. in Healthy Subjects and Patients With Hepatic or Renal Impairment by Monte Carlo Simulation.

The aim of this pharmacokinetic/pharmacodynamic (PK/PD) study is to evaluate the efficacy of various isavuconazole dosing regimens for healthy individuals and patients with hepatic or renal impairment against Aspergillus spp. and Candida spp. Monte Carlo simulations were conducted using pharmacokinetic (PK) parameters and pharmacodynamics (PD) data to determine the probabilities of target attainment and cumulative fractions of response in terms of area under the concentration curve/minimum inhibition concentration (AUC/MIC) targets of isavuconazole. A clinically recommended dosage regimen of isavuconazole (200 mg qd) obtained high cumulative fraction of response values of > 90% for all subjects against A. fumigatus, A. flavus, A. nidulans, A. terreus, A. versicolor, C. parapsilosis and C. tropicalis. For patients with mild or moderate hepatic impairment, the dosage should be halved only when treating invasive fungal infections caused by C. albicans, C. parapsilosis or C. tropicalis. However, dose adjustment is unlikely to be required in mild to severe renal impairment patients because all cumulative fraction of response values were similar to those of comparing with healthy subjects. Notably, all isavuconazole dosing regimens were not effective against C. glabrata and C. krusei in all subjects. These PK/PD-based simulations rationalize and optimize the dosage regimens of isavuconazole for healthy individuals and patients with hepatic or renal impairment against Aspergillus spp. and Candida spp.

Development and validation of a rapid LC-MS/MS method for simultaneous determination of netupitant and palonosetron in human plasma and its application to a pharmacokinetic study.

A simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was firstly developed and validated for simultaneous determination of netupitant and palonosetron in human plasma using ibrutinib as the internal standard (IS). Following liquid-liquid extraction, the compounds were eluted isocratically on a Phenomenex C18 column (50mm×2.0mm, 3µm) with the mobile phase consisting of acetonitrile and 10mM ammonium acetate buffer (pH 9.0) (89:11, v/v) at the flow rate of 0.3mL/min. The monitored ion transitions were m/z 579.5→522.4 for netupitant, m/z 297.3→110.2 for palonosetron and m/z 441.2→138.1 for IS. Chromatographic run time was 2.5min per injection, which made it possible to analyze more than 300 of samples per day. The assay exhibited a linear dynamic range of 5-1000ng/mL for netupitant and 0.02-10ng/mL for palonosetron in plasma. The values for both within- and between-day precision and accuracy were well within the generally accepted criteria for analytical methods (<15%). Selectivity, linearity, lower limit of quantification (LLOQ), accuracy, precision, stability, matrix effect, recovery and carry-over effect were evaluated for all analytes. The method is simple, rapid, and has been applied successfully to a pharmacokinetic study of netupitant and palonosetron in healthy volunteers.

Characterization of the disposition of fostamatinib in Japanese subjects including pharmacokinetic assessment in dry blood spots: results from two phase I clinical studies.

PURPOSE: The aims of the present study were to characterize the pharmacokinetics of fostamatinib in two phase I studies in healthy Japanese subjects after single- and multiple-dose administration, and to evaluate the utility of dried blood spot (DBS) sampling. METHODS: In study A, 40 Japanese and 16 white subjects were randomized in a double-blind parallel group study consisting of seven cohorts, which received either placebo or a fostamatinib dose between 50 and 200 mg after single and multiple dosing. Pharmacokinetics of R406 (active metabolite of fostamatinib) in plasma and urine was assessed, and safety was intensively monitored. Study B was an open-label study that assessed fostamatinib 100 and 200 mg in 24 Japanese subjects. In addition to plasma and urine sampling (as for study A), pharmacokinetics was also assessed in blood. RESULTS: Mean maximum plasma concentration (C max) and area under total plasma concentration­time curve (AUC) increased with increasing dose in Japanese subjects. Steady state was achieved in 5­7 days for all doses. C max and AUC were both higher in Japanese subjects administered a 150-mg single dose than in white subjects. This difference was maintained for steady state exposure by day 10. Overall, R406 blood concentrations were consistent and ∼2.5-fold higher than in plasma. Minimal (<0.1 %) R406 was excreted in urine. Fostamatinib was well tolerated at all doses. CONCLUSIONS: Fostamatinib pharmacokinetics following single- and multiple-dose administration was approximately dose proportional at all doses ≤150 mg and greater than dose proportional at 200 mg in Japanese subjects. Japanese subjects administered fostamatinib 150 mg had higher exposure than white subjects. R406 could be measured in DBS samples and distributed into red blood cells, and DBS sampling was a useful method for assessing R406 pharmacokinetics.

[Simultaneous determination of clevidipine butyrate and its metabolite clevidipine acid in dog blood by liquid chromatography-tandem mass spectrometry].

A rapid, sensitive and simple liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous determination of clevidipine butyrate and its primary metabolite clevidipine acid in dog blood. After one-step protein precipitation with methanol, the chromatographic separation was carried out on an Ecosil C18 column (150 mm x 4.6 mm, 5 µm) with a gradient mobile phase consisting of methanol and 5 mmol · L(-1) ammonium formate. A chromatographic total run time of 13.0 min was achieved. The quantitation analysis was performed using multiple reaction monitoring (MRM) at the specific ion transitions of m/z 454.1 [M-H]- --> m/z 234.1 for clevidipine butyrate, m/z 354.0 [M-H]- --> m/z 208.0 for clevidipine acid and m/z 256.1 [M-H]- --> m/z 227.1 for elofesalamide (internal standard, IS) in the negative ion mode with electrospray ionization (ESI) source. The linear calibration curves for clevidipine butyrate and clevidipine acid were obtained in the concentration ranges of 0.5-100 ng · mL and 1-200 ng · mL(-1), separately. The lower limit of quantification of clevidipine butyrate and clevidipine acid were 0.5 ng · mL(-1) and 1 ng · mL(-1). The intra and inter-assay precisions were all below 12.9%, the accuracies were all in standard ranges. Stability testing indicated that clevidipine butyrate and clevidipine acid in dog blood with the addition of denaturant methanol was stable under various processing and/or handling conditions. The validated method has been successfully applied to a pharmacokinetic study of clevidipine butyrate injection to 8 healthy Beagle dogs following intravenous infusion at a flow rate of 5 mg · h(-1) for 0.5 h.

Pharmacokinetic-pharmacodynamic modeling of fostamatinib efficacy on ACR20 to support dose selection in patients with rheumatoid arthritis (RA).

R788 (fostamatinib) is an oral prodrug that is rapidly converted into a relatively selective spleen tyrosine kinase (SYK) inhibitor R406, evaluated for the treatment of rheumatoid arthritis (RA). This analysis aimed at developing a pharmacodynamic model for efficacy using pooled ACR20 data from two phase II studies in patients with rheumatoid arthritis (TASKi1 and TASKi2), describing the effect of fostamatinib as a function of fostamatinib exposure (dose, R406 plasma concentration) and other explanatory variables. The exposure-response relationship of fostamatinib was implemented into a continuous time Markov model describing the time course of transition probabilities between the three possible states of ACR20 non-responder, responder, and dropout at each visit. The probability of transition to the ACR20 response state was linearly (at the rate constant level) related to average R406 plasma concentrations and the onset of this drug effect was fast. Further, increases of fostamatinib dose resulted in increased dropout and subsequent loss of efficacy. This analysis provided an increased understanding of the exposure-response relationship, and provided support for fostamatinib 100 mg BID an appropriate dose regimen for further clinical evaluation.

UPLC-MS/MS method for determination of bepotastine in human plasma.

A sensitive and rapid method for quantitation of bepotastine in human plasma has been established using ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). Valsartan was used as an internal standard. Bepotastine and internal standard in plasma sample were extracted using ethylacetate (liquid-liquid extraction). A centrifuged upper layer was then evaporated and reconstituted with the mobile phase of acetonitrile--5 mM ammonium formate (pH 3.5) (85:15, v/v). The reconstituted samples were injected into a phenyl column. Using MS/MS in the multiple reaction monitoring mode, bepotastine and valsartan were detected without severe interference from human plasma matrix. Bepotastine produced a protonated precursor ion ([M+H](+)) at m/z 389 and a corresponding product ion at m/z 167. And the internal standard produced a protonated precursor ion ([M+H](+)) at m/z 436 and a corresponding product ion at m/z 291. Detection of bepotastine in human plasma by the UPLC-ESI-MS/MS method was accurate and precise with a quantitation limit of 0.2 ng/mL. The validation, reproducibility, stability and recovery of the method were evaluated. The method has been successfully applied to pharmacokinetic studies of bepotastine in human plasma.

External validation of the bilirubin-atazanavir nomogram for assessment of atazanavir plasma exposure in HIV-1-infected patients.

Atazanavir increases plasma bilirubin levels in a concentration-dependent manner. Due to less costly and readily available assays, bilirubin has been proposed as a marker of atazanavir exposure. In this work, a previously developed nomogram for detection of suboptimal atazanavir exposure is validated against external patient populations. The bilirubin nomogram was validated against 311 matching bilirubin and atazanavir samples from 166 HIV-1-infected Norwegian, French, and Italian patients on a ritonavir-boosted regimen. In addition, the nomogram was evaluated in 56 Italian patients on an unboosted regimen. The predictive properties of the nomogram were validated against observed atazanavir plasma concentrations. The use of the nomogram to detect non-adherence was also investigated by simulation. The bilirubin nomogram predicted suboptimal exposure in the patient populations on a ritonavir-boosted regimen with a negative predictive value of 97% (95% CI 95-100). The bilirubin nomogram and monitoring of atazanavir concentrations had similar predictive properties for detecting non-adherence based on simulations. Although both methods performed adequately during a period of non-adherence, they had lower predictive power to detect past non-adherence episodes. Using the bilirubin nomogram for detection of suboptimal atazanavir exposure in patients on a ritonavir-boosted regimen is a rapid and cost-effective alternative to routine measurements of the actual atazanavir exposure in plasma. Its application may be useful in clinical settings if atazanavir concentrations are not available.

Comparison of extraction procedures for assessment of matrix effect for selective and reliable determination of atazanavir in human plasma by LC-ESI-MS/MS.

A comparative study with three conventional extraction techniques namely protein precipitation (PP), liquid-liquid extraction (LLE) and solid phase extraction (SPE) has been demonstrated to assess the magnitude of matrix interference by post-column analyte infusion and post extraction analyte spiking for the determination of atazanavir from human plasma. Severe ion suppression observed in PP and to a lesser extent in LLE was circumvented by SPE on LiChrosep Sequence extraction cartridge. Based on these observations a selective, rugged and high throughput SPE-LC-MS/MS method has been developed for reliable determination of atazanavir in human plasma. The chromatographic separation was achieved on a Hypersil Gold C18 (50mm×4.6mm, 5µm) analytical column using 5mM ammonium formate in water:methanol (10:90, v/v) as the mobile phase under isocratic conditions. The method was validated over a wide dynamic concentration range of 10-6000ng/mL. The mean relative recovery and absolute matrix effect across quality controls were 84.9 and 93.2%, respectively. The precision value for relative matrix effect between eight different lots of plasma, expressed as %CV of the slopes of the calibration lines was 2.41. The stability of atazanavir under different storage conditions varied from -8.4 to 5.4%. The method was successfully applied to a bioequivalence study of 300mg atazanavir capsule formulation in 24 healthy Indian males under fasting condition.

Incidence and management of ischemic stroke and intracerebral hemorrhage in patients on dabigatran etexilate treatment.

Dabigatran etexilate is an oral, reversible direct thrombin inhibitor and has been recently approved for the prevention of stroke in patients with non-valvular atrial fibrillation. This review describes the incidence and management of stroke and related complications in patients on dabigatran etexilate. Dabigatran is a rapidly acting, and highly selective and reversible inhibitor of thrombin. It also has a potent inhibitory effect on thrombin-induced platelet aggregation, making it effective in preventing both venous and arterial thrombosis. The activated partial thromboplastin time, ecarin clotting time and thrombin time are sensitive tests to evaluate the anticoagulant effects of dabigatran. The rate of ischemic stroke is significantly lower in patients on 150 mg of dabigatran etexilate as compared to 110-mg dose or warfarin (9.2, 13.4, 12 per 1,000 patients, respectively). As there is no standard coagulation test for dabigatran; treatment of acute stroke in such patients is debatable. Careful clinical consideration is required before administering thrombolytic therapy in this patient population. The rate of hemorrhagic stroke was 1.2 and 1.0 per 1,000 patients treated on 110 and 150 mg of dabigatran, respectively. As there is no specific antidote, the only treatment option is discontinuation of the drug and supportive management. Other treatment options, though not clinically proven, include specific reversal agents, which can be individualized according to the severity of the hemorrhage. Dabigatran should be discontinued before invasive procedures depending on the degree of renal impairment and risk of bleeding.

Atazanavir metabolism according to CYP3A5 status: an in vitro-in vivo assessment.

The current study was a follow-up to an in vivo study in which atazanavir oral clearance was shown to be dependent on genetically determined CYP3A5 expression status, but only in non-African Americans. The aim of this study was to identify atazanavir metabolites generated by CYP3A5 and to evaluate this metabolite pattern in the African-American versus non-African-American CYP3A5 expressors from the previous study. First, the in vitro metabolism of atazanavir was evaluated using human liver microsomes (HLM) and CYP3A4 and CYP3A5 isoforms. Second, the metabolite pattern generated by CYP3A5 was evaluated in human plasma samples from the previous study. Atazanavir metabolites were analyzed using liquid chromatography-tandem mass spectrometry methods. Metabolite areas under the time-concentration curves (AUCs) were normalized to atazanavir AUC to generate an AUC ratio. Sixteen metabolites were observed in human liver microsomal incubations representing five "phase I" biotransformation pathways. Mono-oxidation products (M1 and M2) were formed by CYP3A5 at a faster rate than CYP3A4 by 32- and 2.6-fold, respectively. This finding was replicated in HLM from a genetically determined CYP3A5 expressor versus nonexpressor. In the in vivo samples, the M1 and M2 AUC ratios were approximately 2-fold higher in CYP3A5 expressors versus nonexpressors (P < 0.05), and the difference was similar in African Americans and non-African Americans. Thus, CYP3A5 produced a unique metabolite "signature" for atazanavir in vitro and in vivo, independent of race. Therefore, other pharmacological factors are likely to explain the apparent lack of effect of genetically determined CYP3A5 expressor status on atazanavir oral clearance in African Americans from the previous study.

LC-MS-ESI for the determination of loratadine and descarboethoxyloratadine in human plasma.

A rapid, sensitive, and accurate liquid chromatography-tandem mass spectrometry assay for simultaneous determination of loratadine (L) and its active metabolite, descarboethoxyloratadine (DCL), in human plasma is developed using desipramine as internal standard (IS). The analytes and IS are separated on a Betabasic cyano (100 mm x 2.1 mm, 5 microm) column and detected by tandem mass spectrometry with a turbo ion spray interface operating in positive ion and multiple reaction monitoring acquisition mode. The total chromatographic runtime is 3.0 min with retention time for L, DCL, and IS at 0.82, 1.58, and 1.97 min, respectively. The method is validated over a dynamic linear range of 0.05-15.00 ng/mL for both L and DCL with a correlation coefficient of r(2) 0.9984 and 0.9979, respectively. The intra-batch and inter-batch precision (%CV) across five levels (LLOQ, LQC, MQC, HQC, and ULOQ) is less than 9%. The method is successfully applied to a bioequivalence study of 10 mg loratadine tablet formulation in 28 healthy Indian male subjects under fasted condition.

Full validation of an analytical method for the HIV-protease inhibitor atazanavir in combination with 8 other antiretroviral agents and its applicability to therapeutic drug monitoring.

Because HIV medications are used in combination, it is important to develop multiplex assays to streamline the therapeutic drug monitoring process and provide rapid turnaround. This article reports full validation of an analytical method that combines atazanavir with 6 HIV-protease inhibitors (indinavir, amprenavir, saquinavir, nelfinavir, ritonavir, and lopinavir) and 2 nonnucleoside reverse transcriptase inhibitors (nevirapine and efavirenz). Using 200 microL of plasma and a simple liquid-liquid extraction method, this analytical method achieved a clean baseline and high extraction efficiencies (90.0% to 99.5%). A Zorbax C-18 (150 x 4.6 mm, 3.5 microm) analytical column was used along with a 27-minute linear gradient elution of the mobile phase to provide sharp peaks at 210 nm. This method was validated over a range of 25 to 10,000 ng/mL and is accurate (90.4% to 110.5%) and precise (precision within a day and between days ranged from 2.3% to 8.3%). Because this method is simple and inexpensive, it may have applicability in countries with low resources.

Assessment of DNA damage in WBCs of workers occupationally exposed to fumes and aerosols of bitumen.

We conducted a cross-shift study with 66 bitumen-exposed mastic asphalt workers and 49 construction workers without exposure to bitumen. Exposure was assessed using personal monitoring of airborne bitumen exposure, urinary 1-hydroxypyrene (1-OHP), and the sum of 1-, 2 + 9-,3-,4-hydroxyphenanthrene (OHPH). Genotoxic effects in WBC were determined with nonspecific DNA adduct levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and the formation of DNA strand breaks and alkali-labile sites. Concentration of fumes and aerosols of bitumen correlated significantly with the concentrations of 1-OHP and OHPH after shift (r(s) = 0.27; P = 0.03 and r(s) = 0.55; P < 0.0001, respectively). Bitumen-exposed workers had more DNA strand breaks than the reference group (P < 0.0001) at both time points and a significant correlation with 1-OHP and OHPH in the postshift urines (r(s) = 0.32; P = 0.001 and r(s) = 0.27; P = 0.004, respectively). Paradoxically, we measured higher levels of DNA strand breaks, although not significant, in both study groups before shift. 8-OxodGuo adduct levels did not correlate with DNA strand breaks. Further, 8-oxodGuo levels were associated neither with personal exposure to bitumen nor with urinary metabolite concentrations. Significantly more DNA adducts were observed after shift not only in bitumen-exposed workers but also in the reference group. Only low-exposed workers had significantly elevated 8-oxodGuo adduct levels before as well as after shift (P = 0.0002 and P = 0.02, respectively). Our results show that exposure to fumes and aerosols of bitumen may contribute to an increased DNA damage assessed with strand breaks.

Biomarkers for assessment of pharmacologic activity for a vascular endothelial growth factor (VEGF) receptor inhibitor, PTK787/ZK 222584 (PTK/ZK): translation of biological activity in a mouse melanoma metastasis model to phase I studies in patients with advanced colorectal cancer with liver metastases.

PTK/ZK is a novel, oral angiogenesis inhibitor that specifically targets all 3 vascular endothelial growth factor (VEGF) receptor tyrosine kinases and is currently in phase III clinical trials. In early clinical trials, PTK/ZK demonstrated a dose-dependent reduction in tumor vascular parameters as measured by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and an acute increase in plasma VEGF levels. The reduction in tumor vascularity was significantly correlated with improved clinical outcome in patients with advanced colorectal cancer and liver metastases. To assess the predictive value of a mouse model of tumor metastases, comparisons were performed for the biological activity of PTK/ZK in the mouse model and in patients with liver metastases in the clinical phase I trials. An orthotopic, syngeneic mouse model was used: C57BL/6 mice injected in the ear with murine B16/BL6 melanoma cells which metastases to the cervical lymph-nodes. The primary tumor and spontaneous metastases express VEGF and VEGF receptors and respond to treatment with VEGFR tyrosine kinase inhibitors. PTK/ZK was administered orally, with assessments by DCE-MRI of the metastases and plasma VEGF taken predose and at 3 days posttreatment and efficacy determined at 7 days posttreatment. Dose-ranging studies in naive mice provided preclinical pharmacokinetic data, while two dose-escalation phase I studies provided clinical pharmacokinetic data. An exposure-response relationship was observed both for mouse metastases (measured as % tumor weight treated/control) and for human liver metastases (measured as % regression). In the B16/BL6 model, the active dose of 50 mg/kg PTK/ZK yielded 62.4 (+/- 16.0) h microM plasma exposure, which is comparable to the plasma area under the concentration time curve (AUC) achieved by the 1000 mg dose of PTK/ZK used in clinical trials. At this exposure level in clinical trials, DCE-MRI showed a reduction in the area under the enhancement curve (IAUC) to 47% of baseline. At a similar exposure in the PTK/ZK-treated mice, a reduction in IAUC to 75% of baseline was observed. Furthermore, at doses of 50 mg/kg PTK/ZK and above, an increase in plasma VEGF level 10 h after drug administration was observed in mice which was consistent with findings from the clinical trials. In conclusion, the preclinical pharmacodynamics of PTK/ZK correlate well with clinical activity in phase I trials over comparable exposures to the drug. Thus, data from this preclinical model proved to be consistent with and thus predictive of the biologic effects of PTK/ZK in phase I/II clinical trials.

Quantification of zolpidem in human plasma by liquid chromatography-electrospray ionization tandem mass spectrometry.

A simple and robust method for quantification of zolpidem in human plasma has been established using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS). Es-citalopram was used as an internal standard. Zolpidem and internal standard in plasma sample were extracted using solid-phase extraction cartridges (Oasis HLB, 1 cm3/30 mg). The samples were injected into a C8 reversed-phase column and the mobile phase used was acetonitrile-ammonium acetate (pH 4.6; 10 mm) (80:20, v/v) at a flow rate of 0.7 mL/min. Using MS/MS in the selected reaction-monitoring (SRM) mode, zolpidem and Es-citalopram were detected without any interference from human plasma matrix. Zolpidem produced a protonated precursor ion ([M+H]+) at m/z 308.1 and a corresponding product ion at m/z 235.1. The internal standard produced a protonated precursor ion ([M+H]+) at m/z 325.1 and a corresponding product ion at m/z 262.1. Detection of zolpidem in human plasma by the LC-ESI MS/MS method was accurate and precise with a quantification limit of 2.5 ng/mL. The proposed method was validated in the linear range 2.5-300 ng/mL. Reproducibility, recovery and stability of the method were evaluated. The method has been successfully applied to bioequivalence studies of zolpidem.

[TS-1 treatment for progressive gastric cancer in a patient on chronic dialysis--assessment of dosage regimen by monitoring blood concentrations of therapeutic drugs (TDM)].

The optimum dose of TS-1 for the treatment of peritoneally disseminated gastric cancer in a patient with chronic renal failure undergoing chronic dialysis was estimated by monitoring the blood concentrations of 5-FU and gimeracil (CDHP) [therapeutic drug monitoring (TDM)] during administration of TS-1. Immediately after dialysis, 50 mg or 40 mg of TS-1, corresponding to 50% and 40% of the standard dose (100mg for this patient), respectively, was administered orally once a day every other day, and TDM was conducted. Compared with the pharmacokinetic parameters of 5-FU at the time of the initial administration of 50 mg or 40 mg of TS-1 and that of cancer patients with normal renal function, the AUC shown in the administration of 40 mg was equivalent to that observed with a single safe dose of 100 mg in patients with normal renal function. Based on this observation, the daily TS-1 dose was set at 40 mg in this patient, and TS-1 treatment was started after confirming the absence of the accumulation of 5-FU or CDHP during repeated administrations. In this treatment protocol, TS-1 was administered 11 times at a daily dose of 40 mg every other day immediately after dialysis, followed by a rest. This .administration schedule was defined as one course. Under these conditions, the patient was treated on an outpatient basis, and the treatment could be safely continued without the development of any severe adverse events, such as myelosuppression.