Ren-ai Xu

Determination of piracetam in rat plasma by LC–MS/MS and its application to pharmacokinetics

A sensitive and selective liquid chromatography-tandem mass spectrometry method for the determination of piracetam in rat plasma was developed and validated over the concentration range of 0.1-20 µg/mL. After addition of oxiracetam as internal standard, a simplified protein precipitation with trichloroacetic acid (5%) was employed for the sample preparation. Chromatographic separation was performed by a Zorbax SB-Aq column (150 × 2.1 mm, 3.5 µm). The mobile phase was acetonitrile-1% formic acid in water (10:90 v/v) delivered at a flow rate of 0.3 mL/min. The MS data acquisition was accomplished in multiple reaction monitoring mode with a positive electrospray ionization interface. The lower limit of quantification was 0.1 µg/mL. For inter-day and intra-day tests, the precision (RSD) for the entire validation was less than 9%, and the accuracy was within the 94.6-103.2% range. The developed method was successfully applied to pharmacokinetic studies of piracetam in rats following single oral administration dose of 50 mg/kg.

Determination of curdione in rabbit plasma by liquid chromatography mass spectrometry

A sensitive and selective liquid chromatography mass spectrometry method for determination of curdione in rabbit plasma was developed. After addition of tramadol as internal standard (IS), protein precipitation by acetonitrile was used for sample preparation. Chromatographic separation was achieved on a Zorbax SB-C₁₈ (2.1 × 50 mm, 3.5 µm) column with acetonitrile-0.1% formic acid as mobile phase with gradient elution. An electrospray ionization source was applied and operated in positive-ion mode; selective ion monitoring was used for quantification using target fragment ions m/z 237 for curdione and m/z 264 for the IS. Calibration plots were linear over the range of 20-4000 ng/mL for curdione in plasma. The lower limit of quantification for curdione was 20 ng/mL. Mean recovery of curdione from plasma was in the range 94.3-98.4%. The RSD of intra-day and inter-day precision were both less than 9%. This method is simple and sensitive enough to be used in pharmacokinetic research for the determination of curdione in rabbit plasma.

Successful Management of Voriconazole-Associated Hyponatremia with Therapeutic Drug Monitoring

Voriconazole is a broad-spectrum triazole antifungal agent and the first-choice therapy for invasive aspergillosis (IA) (1). Although voriconazole is generally well tolerated, anecdotal case reports have described unexpected severe adverse events related to voriconazole, such as hyponatremia, which potentially could result in death (2–4). We report a case of successful voriconazole treatment of invasive pulmonary aspergillosis (IPA) in a hyponatremia patient. A 72-year-old man with a 10-year history of chronic obstructive pulmonary disease (COPD) was admitted to our respiratory department because of acute exacerbation. Because of his positive aspergillus sputum cultures before admission, he had a higher risk of developing IPA. The patient was treated with intravenous voriconazole (two loading doses of 6 mg/kg of body weight and then 4 mg/kg every 12 h) for 2 weeks and then changed to oral voriconazole tablets at a dose of 200 mg every 12 h. A definite diagnosis of IPA was soon obtained from a computed tomography (CT)guided percutaneous lung biopsy specimen evidencing Aspergillus fumigatus in culture (5). Twenty-six days after commencing voriconazole therapy, the patient showed somnolence and malaise symptoms. Electrolyte levels showed that his sodium level was 104 mmol/liter but that his potassium and creatinine levels were normal. Therapeutic drug monitoring (TDM) was performed, and the voriconazole plasma trough concentration (voriconazole C0) was high (7.10 g/ml). Two days after the discontinuation of voriconazole and infusion of 3% saline, the patient’s mental status and hyponatremia recovered. Our goal voriconazole C0 range was 1.0 to 5.5 g/ml. The voriconazole C0 (0.68 g/ml), obtained 11 days after a half-dose reduction of voriconazole (200 mg/day), was not within the therapeutic range. Since his voriconazole C0 remained subtherapeutic (0.68 g/ml), we increased the dose to 300 mg/day after he was discharged from the hospital. Thirteen days after the treatment, the voriconazole C0 increased to 1.38 g/ml, which mostly achieved the target concentration of 1.0 g/ml. The patient remained asymptomatic, and repeat CT findings showed near resolution of lung lesions upon follow-up in our outpatient department. The CYP2C19 genotype was classified as heterozygous extensive metabolizer (CYP2C19*1/CYP2C19*2). It is well known that CYP2C19 genetic polymorphisms make it particularly difficult to predict exposure to voriconazole and its potential dose-dependent toxicity (6). Indeed, voriconazole C0s of 1.0 g/ml have been associated with improved responses to therapy and survival (7, 8). Increased adverse events have been associated with voriconazole C0s of 5.0 to 6.0 g/ml (9, 10). As a consequence, TDM may be a useful tool to optimize voriconazole therapy. In our case, the voriconazole C0 was 7.10 g/ml, which is considered in the toxic range. Therefore, voriconazole-associated hyponatremia may be concentration dependent. Instead of discontinuing antifungal therapy, it was decided to reduce the voriconazole dose to 200 mg/day, and the voriconazole C0 was subtherapeutic (0.68 g/ml). Finally, TDM revealed an adequate voriconazole C0 (1.38 g/ml) 13 days after dose adjustment to 300 mg/day, suggesting that the dose regimen for this patient was appropriate. So, voriconazole-related hyponatremia suggests that the clinical utility of routine TDM of voriconazole reduces drugrelated adverse events and improves treatment outcome in invasive fungal infections. In conclusion, this case suggests that fatally severe hyponatremia can develop after initiation of voriconazole antifungal therapy. Furthermore, this experience confirms that the appropriateness of voriconazole dose adjustment instead of therapy interruption should be considered according to the voriconazole C0. We believe that TDM is useful to determine the voriconazole dosage in a voriconazole-related hyponatremia patient.

Therapeutic drug monitoring in voriconazole-associated hyponatremia.

Voriconazole is a second generation triazole antifungal agent and the first choice therapy for invasive aspergillosis (IA). Although voriconazole may be associated with many adverse events, hyponatremia has been rarely reported which potentially could result in death. Therapeutic drug monitoring (TDM) and individualization of therapy by measuring voriconazole plasma concentrations improved the efficacy and safety in patients. We report the effect of TDM to adjust voriconazole dosage in a voriconazole-related hyponatremia patient.

Effect of Repeated Wuniu Early Tea Administration on the CYP450 Activity Using a Cocktail Method

Wuniu early tea (Camellia sinensis) is an important beverage consumed in China. Up to date, a lot of methods for identifying and chemical analysing have been done. However, there is no report on the effects of Wuniu early tea on cytochrome P450 isozymes. Therefore, the present objective of our study was to evaluate the potential effects of Wuniu early tea on cytochrome P450 isozymes P2C9, P1A2, P2C19 and P2B6 in rats with a cocktail approach including, matching probe drugs of tolbutamide, phenacetin, omeprazole and bupropion. These four probe drugs were simultaneously administered to rats after repeated Wuniu early tea administration. The pharmacokinetics of the probes in the plasma was simultaneous determined by high-performance liquid chromatography-mass spectrometry. The t1/2 and AUC(0-∞) of tolbutamide increased significantly and CLz decreased remarkably in test rats after repeated Wuniu early tea administration. However, the main pharmacokinetic parameters of the other three probe drugs were not significantly different between control and test rats. The findings in this study suggested that Wuniu early tea could inhibit cytochrome P2C9 while did not influence on cytochrome P1A2, cytochrome P2C19 and cytochrome P2B6.