The rise and fall of felbamate as a treatment for partial epilepsy--aplastic anemia and hepatic failure to blame?

Felbamate has been approved for refractory partial seizures since the early nineties. Due to safety concerns regarding its use, namely, in aplastic anemia and hepatic failure, felbamate's use has been restricted and a 'Black Box' warning has been inserted. Nonetheless, it is a useful drug in refractory cases of partial epilepsy. There are certain precautions which can prevent and minimize the serious idiosyncratic reactions associated with felbamate, thereby providing an option in refractory cases where no other drug works.

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.

Potential pharmacodynamic drug-drug interaction between concomitantly administered lisinopril and diclofenac sodium: a call for appropriate management in hypertensive osteoarthritic patients.

BACKGROUND: The present study was designed as an open label, multiple-dose, randomized, parallel trial to evaluate the pharmacodynamic drug-drug interaction of lisinopril and concomitantly administered diclofenac sodium in non-diabetic and diabetic, mild to moderate hypertensive, osteoarthritic patients. METHODS: Post-screening and on inclusion, patients were put on a 2-week washout period and then randomly assigned to either only lisinopril 10 mg or combination of lisinopril 10 mg and diclofenac sodium 100 mg treatments for 8-12 weeks in diseased states of hypertension and osteoarthritis with or without type 2 diabetes mellitus. RESULTS: The blood pressure (BP) control with lisinopril was reduced by concomitantly administered diclofenac sodium in non-diabetic (SBP: p=0.00002; DBP: p=0.000008) and diabetic (SBP: p=0.002; DBP: p=0.001) patients when compared with the patients receiving lisinopril alone. Insulin sensitivity was improved (p=0.00002) and urinary albumin excretion rate was better controlled (p=0.0096) in lisinopril-treated patients when compared with the combination treatment in diabetic pool. Serum creatinine levels increased significantly in non-diabetic patients (p=0.00004) receiving combination treatment. In addition, creatinine clearance (CLCR) and blood urea nitrogen (BUN) were significantly higher in diabetic (CLCR: p<0.00001; BUN: p=0.0098) as well as in non-diabetic (CLCR: p<0.00001; BUN: p=0.03) patients treated with combination treatment. The alterations in serum electrolytes, reduction in % platelet aggregation activity and improvement in lipid profile was more profound with combination treatment in comparison to lisinopril alone. CONCLUSIONS: The antihypertensive efficacy and insulin sensitivity improving property of lisinopril along with the renal function might get worse in hypertensive osteoarthritic patients receiving concomitant treatment of oral diclofenac sodium with lisinopril. In addition to this, close monitoring of serum electrolytes is also suggested to rule out any long-term detrimental effect.

Selective determination of antiretroviral agents tenofovir, emtricitabine, and lamivudine in human plasma by a LC-MS-MS method for a bioequivalence study in healthy Indian subjects.

A selective, sensitive, rugged, and high throughput liquid chromatography tandem mass spectrometry method is developed for the determination of one nucleotide tenofovir (TFV) and two nucleosides emtricitabine (FTC) and lamivudine (3TC) reverse transcriptase inhibitors in human plasma. Plasma samples were prepared by solid-phase extraction of the analytes and acyclovir (ACV) as internal standard using Waters Oasis MCX cartridges. The chromatographic separation is achieved in a run-time of 3.0 min on an ACE 5 CN column (150 mm × 4.6 mm, 5 µm) under isocratic conditions. The mobile phase consisted of 0.5% formic acid in water and acetonitrile (55:45, v/v). The protonated precursor --> product ion transitions for TFV, FTC, 3TC, and internal standard were monitored on a triple quadrupole mass spectrometer operating in the multiple reaction monitoring (MRM) and positive ion mode. A linear dynamic range of 4.0-802 ng/mL, 15.0-3006 ng/mL, and 20.1-4023 ng/mL is established for TFV, FTC, and 3TC, respectively, using 0.2 mL plasma sample. The method is fully validated for its sensitivity, selectivity, accuracy and precision, ion suppression, matrix effect, recovery, stability, and dilution integrity. It is successfully applied to a bioequivalence study of [300(TFV) + 200(FTC) + 300(3TC)] mg tablet formulation in 43 healthy human subjects under fasting conditions.

Application of a rapid and selective method for the simultaneous determination of protease inhibitors, lopinavir and ritonavir in human plasma by UPLC-ESI-MS/MS for bioequivalence study in Indian subjects.

A high throughput and rugged ultra performance liquid chromatography tandem mass spectrometry (UPLC-ESI-MS/MS) method is developed and validated for the selective determination of protease inhibitors -- lopinavir (LPV) and ritonavir (RTV) in human plasma. Plasma samples were prepared by solid phase extraction of the analytes and their deuterated analogs as internal standard (IS) using Waters Oasis HLB cartridges. The chromatographic separation was achieved in a run time of 1.2 min on Waters Acquity UPLC BEH C18 column (50 mm x 2.1 mm, 1.7 microm) under isocratic conditions. The mobile phase consisted of 10 mM ammonium formate, pH 4.0 adjusted with formic acid and methanol (10:90, v/v). The protonated precursor --> product ion transitions for lopinavir, ritonavir, d(8)-lopinavir and d(6)-ritonavir were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) and positive ion mode. A linear dynamic range of 2.9-1452 ng/mL and 29.6-14379 ng/mL was established for ritonavir and lopinavir respectively using 0.1 mL human plasma. The mean relative recovery of lopinavir (96.6%), ritonavir (97.5%), d(8)-lopinavir (85.5%) and d(6)-ritonavir (86.3%) from spiked plasma samples was consistent and reproducible. The method was successfully applied to a bioequivalence study of [200(lopinavir)+50(ritonavir)]mg tablet formulation in 36 healthy human subjects under fasting conditions.

Rapid and specific liquid chromatographic tandem mass spectrometric determination of tenofovir in human plasma and its fragmentation study.

A simple, specific, and high throughput liquid chromatography tandem mass spectrometry method is developed for the determination of tenofovir, a nucleotide reverse transcriptase inhibitor, in human plasma using adefovir as internal standard. Plasma samples are prepared by solid-phase extraction of the analyte and internal standard using Waters Oasis MCX cartridges (1 cc, 30 mg). The chromatographic separation is achieved on a reversed-phase Chromolith, C18 analytical column (100 mmx4.6 mm, 5 microm) under isocratic conditions. The mobile phase consists of 0.5% formic acid in water and acetonitrile (90:10, v/v) to give a run time of 1.8 min. The protonated precursor-->product ion transitions for tenofovir and IS are monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ion mode. The fragmentation pathways for tenofovir are studied by varying the collision energy (5-55 V) using nitrogen as CAD gas. A linear dynamic range of 3.1-1002.0 ng/mL is established using 0.2 mL plasma sample. The method is fully validated for its sensitivity, selectivity, accuracy and precision, matrix effect, recovery, stability, and dilution integrity. It is applied to a bioequivalence study in 43 human subjects after oral administration of 300 mg tablet formulation under fasting conditions.

Stability evaluation and sensitive determination of antiviral drug, valacyclovir and its metabolite acyclovir in human plasma by a rapid liquid chromatography-tandem mass spectrometry method.

A simple, sensitive and high throughput liquid chromatography/positive-ion electrospray ionization mass spectrometry (LC-ESI-MS/MS) method has been developed for the simultaneous determination of valacyclovir and acyclovir in human plasma using fluconazole as internal standard (IS). The method involved solid phase extraction of the analytes and IS from 0.5 mL human plasma with no reconstitution and drying steps (direct injection of eluate). The chromatographic separation was achieved on a Gemini C18 analytical column using isocratic mobile phase, consisting of 0.1% formic acid and methanol (30:70 v/v), at a flow-rate of 0.8 mL/min. The precursor-->product ion transition for valacyclovir (m/z 325.2-->152.2), acyclovir (m/z 226.2-->152.2) and IS (m/z 307.1-->220.3) were monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring (MRM) mode. The method was validated over the concentration range 5.0-1075 ng/mL and 47.6-10225 ng/mL for valacyclovir and acyclovir respectively. The mean recovery of valacyclovir (92.2%), acyclovir (84.2%) and IS (103.7%) from spiked plasma samples was consistent and reproducible. The bench top stability of valacyclovir and acyclovir was extensively evaluated in buffered and unbuffered plasma. It was successfully applied to a bioequivalence study in 41 healthy human subjects after oral administration of 1000 mg valacyclovir tablet formulation under fasting condition.

Microdetermination of emtricitabine in human plasma by liquid chromatography/tandem mass spectrometry.

A simple, precise, and rapid LC/MS/MS method was developed and validated for the quantification of emtricitabine in human plasma using lamivudine as the internal standard (IS). The method involves liquid-liquid extraction of emtricitabine and the IS in diethyl ether-ethyl acetate (50 + 50, v/v) from 0.1 mL human plasma. A Kromasil C18 (150 x 4.6 mm, 5 microm particle size) analytical column was used for the chromatographic separation under isocratic conditions. The parent --> product ion transitions for emtricitabine (m/z 248.0 --> 130.0) and the IS (m/z 230.1 --> 112.0) were monitored on a triple-quadrupole mass spectrometer, operated in the multiple reaction monitoring positive ion mode. The method was validated over the concentration range of 29.2-3110 ng/mL for emtricitabine, with a total chromatographic run time of 1.5 min. Acceptable precision and accuracy were obtained for the concentrations used to prepare the standard curves. The applicability of the method was demonstrated by a pharmacokinetic study conducted with 43 healthy volunteers who were administered a capsule formulation containing 200 mg emtricitabine.

Automated liquid-liquid extraction based on 96-well plate format in conjunction with ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) for the quantitation of methoxsalen in human plasma.

A sensitive, specific and high throughput bioanalytical method using automated sample processing via 96-well plate liquid-liquid extraction and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) has been developed for the determination of methoxsalen in human plasma. Plasma samples with ketoconazole as internal standard (IS) were prepared by employing 0.2 mL human plasma in ethyl acetate:dichloromethane (80:20, v/v). The chromatographic separation was achieved on a Waters Acquity UPLC BEH C18 column using isocratic mobile phase, consisting of 10 mM ammonium formate and acetonitrile (60:40, v/v), at a flow rate of 0.5 mL/min. The linear dynamic range was established over the concentration range 1.1-213.1 ng/mL for methoxsalen. The method was rugged and rapid with a total run time of 1.5 min. It was successfully applied to a pivotal bioequivalence study in 12 healthy human subjects after oral administration of 10 mg extended release methoxsalen formulation under fasting condition.

Effect of collision-activated dissociation gas and collision energy on the fragmentation of dipyridamole and its rapid and sensitive liquid chromatography/electrospray ionization tandem mass spectrometric determination in human plasma.

The effect of nitrogen as the collision-activated dissociation (CAD) gas on the fragmentation of dipyridamole was investigated in the range of 10-90 eV collision energy. The results support the collision model reported elsewhere, that the degree of ion fragmentation increases with the increasing mass of the collision gas. A simple, sensitive and high-throughput liquid chromatography/tandem mass spectrometry (LC/MS/MS) method has been developed for the determination of dipyridamole, a platelet aggregation inhibitor in human plasma, using granisetron as internal standard (IS). The method involved liquid-liquid extraction of the analyte and IS from 0.5 mL human plasma with diethyl ether. The chromatographic separation was achieved under isocratic conditions and the ion transitions for dipyridamole (m/z 505.40 --> 429.60) and the IS (m/z 313.10 --> 138.20) were monitored on a triple quadrupole mass spectrometer, operating in positive ion multiple reaction monitoring (MRM) mode. The method was validated over the concentration range 5.1-4499.1 ng/mL for dipyridamole. The method was rugged and rapid with a total run time of 1.2 min. It was successfully applied to a pivotal bioequivalence study in 67 healthy human subjects after oral administration of a 75 mg extended release formulation under fasting condition.