A single LC–tandem mass spectrometry method for the simultaneous determination of four H2 antagonists in human plasma

An Efficient Ion-Pair Liquid Chromatographic Method for the Determination of Some H2 Receptor Antagonists

A simple, efficient and reliable ion-pair chromatography (IPC) method was developed and validated for the determination of some H2 receptor antagonists including ranitidine (RAN), nizatidine (NIZ) and famotidine (FAM). The use of IPC separations provided improved peak resolution with good peak shape in short analysis time and augmented method selectivity compared with the frequently used RP-C18 methods. A simple isocratic mode with mobile phase containing acetonitrile and 20 mM acetate buffer (50 : 50, v/v) containing 20 mM sodium dodecyl sulfate was used for separation. The flow rate was set at 1.0 mL min(-1), and the effluent was monitored by UV detector at 280 nm FAM and 320 nm for NIZ and RAN. The method was validated in accordance with International Conference on Harmonization guidelines and shown to be suitable for intended applications. The limits of detections and quantitations were 0.008-0.011 and 0.025-0.033 µg mL(-1), respectively. The proposed IPC method was successfully applied for the determination of pharmaceutical dosage forms without prior need for separation. Additionally, the developed method was applied for the determination of RAN in rabbit plasma using NIZ as the internal standard. The method entailed direct injection of the plasma samples after deproteination using methanol. Finally, the proposed IPC method was applied successfully in a pharmacokinetic study for RAN in rabbits after a single oral dose of RAN.

Evaluation of the transporter-mediated herb-drug interaction potential of DA-9801, a standardized dioscorea extract for diabetic neuropathy, in human in vitro and rat in vivo

Background

Drug transporters play important roles in the absorption, distribution, and elimination of drugs and thereby, modulate drug efficacy and toxicity. With a growing use of poly pharmacy, concurrent administration of herbal extracts that modulate transporter activities with drugs can cause serious adverse reactions. Therefore, prediction and evaluation of drug-drug interaction potential is important in the clinic and in the drug development process. DA-9801, comprising a mixed extract of Dioscoreae rhizoma and Dioscorea nipponica Makino, is a new standardized extract currently being evaluated for diabetic peripheral neuropathy in a phase II clinical study.

Method

The inhibitory effects of DA-9801 on the transport functions of organic cation transporter (OCT)1, OCT2, organic anion transporter (OAT)1, OAT3, organic anion transporting polypeptide (OATP)1B1, OATP1B3, P-glycoprotein (P-gp), and breast cancer resistance protein (BCRP) were investigated in HEK293 or LLC-PK1 cells. The effects of DA-9801 on the pharmacokinetics of relevant substrate drugs of these transporters were also examined in vivo in rats.

Results

DA-9801 inhibited the in vitro transport activities of OCT1, OCT2, OAT3, and OATP1B1, with IC₅₀ values of 106, 174, 48.1, and 273 μg/mL, respectively, while the other transporters were not inhibited by 300 μg/mL DA-9801. To investigate whether this inhibitory effect of DA-9801 on OCT1, OCT2, and OAT3 could change the pharmacokinetics of their substrates in vivo, we measured the pharmacokinetics of cimetidine, a substrate for OCT1, OCT2, and OAT3, and of furosemide, a substrate for OAT1 and OAT3, by co-administration of DA-9801 at a single oral dose of 1,000 mg/kg. Pre-dose of DA-9801 5 min or 2 h prior to cimetidine administration decreased the C_max of cimetidine in rats. However, DA-9801 did not affect the elimination parameters such as half-life, clearance, or amount excreted in the urine, suggesting that it did not inhibit elimination process of cimetidine, which is governed by OCT1, OCT2, and OAT3. Moreover, DA-9801 did not affect the pharmacokinetic characteristics of furosemide, as evidenced by its unchanged pharmacokinetic parameters.

Conclusion

Inhibitory effects of DA-9801 on OCT1, OCT2, and OAT3 observed in vitro may not necessarily translate into in vivo herb-drug interactions in rats even at its maximum effective dose.

Quantitative determination of famotidine in human maternal plasma, umbilical cord plasma and urine using high-performance liquid chromatography-mass spectrometry

Liquid chromatography with electrospray ionization mass spectrometry for the quantitative determination of famotidine in human urine, maternal and umbilical cord plasma was developed and validated. The plasma samples were alkalized with ammonium hydroxide and extracted twice with ethyl acetate. The extraction recovery of famotidine in maternal and umbilical cord plasma ranged from 53 to 64% and 72 to 79%, respectively. Urine samples were directly diluted with the initial mobile phase then injected into the HPLC system. Chromatographic separation of famotidine was achieved by using a Phenomenex Synergi™ Hydro-RP™ column with a gradient elution of acetonitrile and 10 mm ammonium acetate aqueous solution (pH 8.3, adjusted with ammonium hydroxide). Mass spectrometric detection of famotidine was set in the positive mode and used a selected ion monitoring method. Carbon-13-labeled famotidine was used as internal standard. The calibration curves were linear (r(2) > 0.99) in the concentration ranges of 0.631-252 ng/mL for umbilical and maternal plasma samples and 0.075-30.0 µg/mL for urine samples. The relative deviation of method was <14% for intra- and inter-day assays, and the accuracy ranged between 93 and 110%. The matrix effect of famotidine in human urine, maternal and umbilical cord plasma was less than 17%.

Fragmentation of toxicologically relevant drugs in positive-ion liquid chromatography-tandem mass spectrometry

The identification of drugs and related compounds by LC-MS-MS is an important analytical challenge in several application areas, including clinical and forensic toxicology, doping control analysis, and environmental analysis. Although target-compound based analytical strategies are most frequently applied, at some point the information content of the MS-MS spectra becomes relevant. In this article, the positive-ion MS-MS spectra of a wide variety of drugs and related substances are discussed. Starting point was an MS-MS mass spectral library of toxicologically relevant compounds, available on the internet. The positive-ion MS-MS spectra of ∼570 compounds were interpreted by chemical and therapeutic class, thus involving a wide variety of drug compound classes, such benzodiazepines, beta-blockers, angiotensin-converting enzyme inhibitors, phenothiazines, dihydropyridine calcium channel blockers, diuretics, local anesthetics, vasodilators, as well as various subclasses of anti-diabetic, antidepressant, analgesic, and antihistaminic drugs. In addition, the scientific literature was searched for available MS-MS data of these compound classes and the interpretation thereof. The results of this elaborate study are presented in this article. For each individual compound class, the emphasis is on class-specific fragmentation, as discussing fragmentation of all individual compounds would take far too much space. The recognition of class-specific fragmentation may be quite informative in determining the compound class of a specific unknown, which may further help in the identification. In addition, knowledge on (class-specific) fragmentation may further help in the optimization of the selectivity in targeted analytical approaches of compounds of one particular class.