Haematocrit corrected analysis of creatinine in dried blood spots through potassium measurement.

We developed a method for the analysis of creatinine in dried blood spot (DBS) samples to facilitate monitoring of renal function in combination with TDM of immunosuppressive drugs for transplant patients outside the hospital. An 8-mm disc of the DBS was punched, extracted and followed by LC-MS/MS analysis. The haematocrit proved to have a significant influence on the analysis of creatinine in DBS samples. As potassium is a suitable marker for haematocrit, we implemented a method for measuring potassium in DBS and correct the creatinine for haematocrit. For both creatinine and K(+) in DBS analytical and DBS, validation was performed, both components met the validation criteria and no other influences beside the haematocrit were detected. To assess the haematocrit correction, samples were compared to the 'golden' standard and plotted before and after correction. The correction showed a great improvement in agreement between the DBS assay and venous blood assay.

Rapid quantification of gabapentin, pregabalin, and vigabatrin in human serum by ultraperformance liquid chromatography with mass-spectrometric detection.

BACKGROUND: Gabapentin (GBP), pregabalin (PRG), and vigabatrin (VIG) are used for the prevention and treatment of epileptic seizures. The developed method was applied to samples from subjects participating in a pharmacokinetic study of GBP. METHODS: Sample pretreatment consisted of adding 20 µL of trichloroacetic acid (30%; vol/vol) and 200 µL of GBP-d4 in acetonitrile as an internal standard to 20 µL of serum. Chromatographic separation was performed on an Acquity separation module using a Kinetex RP18 column. The aqueous and organic mobile phases were 2 mM ammonium acetate supplemented with 0.1% formic acid in water and acetonitrile, respectively. The detection by a tandem quadrupole mass spectrometer, operating in the positive mode using multiple reaction monitoring, was completed within 2 minutes. RESULTS: The method was linear over the range of 0.03-25 mg/L for GBP, 0.03-25 mg/L for PRG, and 0.06-50 mg/L for VIG. The between- and within-run accuracies ranged from 90% to 107%. The between- and within-run imprecisions of the method were <10%. Stability data show no significant decrease of the analytes. A relative matrix effect of -1%, 0.2%, and -5% was determined for GBP, PRG, and VIG, respectively. CONCLUSIONS: A simple and sensitive ultraperformance liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of GBP, PRG, and VIG in human serum. The reported method provided the necessary linearity, precision, and accuracy to allow the determination of GBP, PRG, and VIG for therapeutic drug monitoring and clinical research purposes.

Validated liquid chromatography-tandem mass spectroscopy method for the simultaneous quantification of four antimycotic agents in human serum.

A liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of voriconazole, fluconazole, posaconazole, itraconazole, and hydroxyitraconazole in human serum. A simple protein precipitation was used as sample pretreatment with ketoconazole as the internal standard. Chromatographic separation was performed on a Waters Alliance 2795 liquid chromatography system using a XBridge RP18 column. The mass spectrometer from Micromass was equipped with an electrospray ionization probe operating in the positive mode using multiple reaction monitoring. The method was linear over the range of 0.01 to 5.00 mg/L for itraconazole, 0.01 to 5.00 mg/L for OH-itraconazole, 0.02 to 10.00 mg/L for voriconazole, 0.06 to 30.00 mg/L for fluconazol, and 0.02 to 10.00 mg/L for posaconazole. The between- and within-run accuracy ranged from 92% to 110%. The between- and within-run imprecision of the method was less than 11%. The reported method provided the necessary linearity, precision, and accuracy to allow the determination of four antimycotic agents for therapeutic drug monitoring and pharmacokinetic-pharmacodynamic studies.

Switchability of Gabapentin Formulations: A Randomized Trial to Assess Bioequivalence Between Neurontin and Gabasandoz on the Individual Subject Level.

Generic substitution of antiepileptic drugs is generally not advised by neurologists. The present study investigated the switchability of gabapentin 800 mg tablets (Neurontin and Gabasandoz) using an individual bioequivalence (IBE) study design with two batches of each product and assessed whether between-batch and between-formulation variability in exposure play a significant role in the within-subject variability. The trial was analyzed according to the US Food and Drug Administration (FDA) framework to establish IBE. The IBE was shown between both products with the 95% upper confidence bound of the IBE criterion being -2.01 and -2.31 for area under the concentration-time curve from zero to infinity (AUC0-inf ) and peak plasma concentration (Cmax ), respectively. Subject-by-formulation variability (1.35%) was negligible compared with the within-subject variability of AUC0-inf with Neurontin (19.0%) and Gabasandoz (23.6%). Inclusion of an additional batch did not significantly change this within-subject variability (20.2% and 23.6%, respectively). This study shows that substitution of gabapentin 800 mg tablets of Neurontin and Gabasandoz should be possible without affecting clinical outcomes.

Quantitative analysis of sildenafil and desmethylsildenafil in human serum by liquid chromatography-mass spectrometry with minimal sample pretreatment.

A simple, sensitive and specific liquid chromatography tandem mass spectrometry method with minimal sample pretreatment was developed for the simultaneous analysis of sildenafil and its metabolite desmethylsildenafil in human serum. Sample pretreatment consisted of adding a methanolic solution of the internal standard vardenafil to the samples. After vortexing and centrifugation the samples were directly injected onto the C18 column using gradient elution. The aqueous and organic mobile phases were ammonium acetate 2 mM supplemented with 0.1% formic acid in water and methanol, respectively. The detection by a triple quadrupole mass spectrometer in positive ESI ionization mode was completed within 5 min. The lower limits of quantification for sildenafil and desmethylsildenafil are 1.0 ng/ml. The intra- and inter-day precisions measured as relative standard deviation were within 10% for both compounds over the linear range. Intra- and inter-day accuracy of sildenafil and desmethylsildenafil ranged from 92 to 103%. This method has been used in a clinical pharmacokinetic study of sildenafil in intensive care patients.

Toxicokinetics of ibogaine and noribogaine in a patient with prolonged multiple cardiac arrhythmias after ingestion of internet purchased ibogaine.

BACKGROUND: Ibogaine is an agent that has been evaluated as an unapproved anti-addictive agent for the management of drug dependence. Sudden cardiac death has been described to occur secondary to its use. We describe the clinical effects and toxicokinetics of ibogaine and noribogaine in a single patient. For this purpose, we developed a LC-MS/MS-method to measure ibogaine and noribogaine plasma-concentrations. We used two compartments with first order absorption. CASE DETAILS: The maximum concentration of ibogaine was 1.45 mg/L. Our patient developed markedly prolonged QTc interval of 647ms maximum, several multiple cardiac arrhythmias (i.e., atrial tachycardia and ventricular tachycardia and Torsades des Pointes). QTc-prolongation remained present until 12 days after ingestion, several days after ibogaine plasma-levels were low, implicating clinically relevant noribogaine concentrations long after ibogaine had been cleared from the plasma. The ratio k12/k21 for noribogaine was 21.5 and 4.28 for ibogaine, implicating a lower distribution of noribogaine from the peripheral compartment into the central compartment compared to ibogaine. CONCLUSIONS: We demonstrated a linear relationship between the concentration of the metabolite and long duration of action, rather than with parent ibogaine. Therefore, after (prolonged) ibogaine ingestion, clinicians should beware of long-term effects due to its metabolite.

Dried blood spot sampling of nilotinib in patients with chronic myeloid leukaemia: a comparison with venous blood sampling.

OBJECTIVES: To compare nilotinib concentrations obtained by venous blood sampling and dried blood spot (DBS) in patients with chronic myeloid leukaemia (CML). It was investigated how to predict nilotinib plasma levels on the basis of DBS. METHODS: Forty duplicate DBS and venous blood samples were collected from 20 patients. Capillary blood was obtained by finger prick and spotted on DMPK-C Whatman sampling paper, simultaneously with venous blood sampling. Plasma concentrations were predicted from DBS concentrations using three methods: (1) individual and (2) mean haematocrit correction and (3) the bias between plasma and DBS concentrations. Results were compared using Deming regression and Bland-Altman analysis. KEY FINDINGS: Nilotinib plasma concentrations ranged from 376 to 2663 µg/l. DBS concentrations ranged from 144 to 1518 µg/l. The slope was 0.56 (95% CI, 0.51 to 0.61) with an intercept of -41.68 µg/l (95% CI, -93.78 to 10.42). Mean differences between calculated and measured plasma concentrations were -14.3% (method 1), -14.0% (method 2) and -0.6% (method 3); differences were within 20% of the mean in 73%, 85% and 80% of the samples, respectively. The slopes were respectively 0.96 (95% CI, 0.86 to 1.06), 0.95 (95% CI, 0.86 to 1.03) and 1.00 (95% CI, 0.91 to 1.09). CONCLUSIONS: Plasma concentrations of nilotinib could be predicted on the basis of DBS. DBS sampling to assess nilotinib concentrations in CML patients seems a suitable alternative for venous sampling.

An UPLC-MS detection method for the quantification of five antibiotics in human plasma.

BACKGROUND: An UPLC-MS detection method for the quantification of amikacin, flucloxacillin, meropenem, penicillin G and vancomycin was developed and validated. RESULTS: The calibration curves were found to be linear from 0.47 to 50 mg/l for amikacin, 1.28 to 135 mg/l for flucloxacillin, 0.75 to 80 mg/l for meropenem, 0.38 to 80 mg/l for penicillin G and 0.73 to 80 mg/l for vancomycin. Between- and within-run accuracy was ranged between 85 and 115%. Between and within imprecision expressed as CV was within 15%. CONCLUSION: The validated method was successfully applied to a PK study in very preterm and small for gestational age infants treated for nosocomial sepsis and/or meningitis.