A simple and sensitive LC-MS/MS method for the determination of sotalol in rat plasma.

A sensitive, rapid and robust HPLC method with tandem mass spectrometry (HPLC/MS/MS) detection has been developed and validated for the quantification of sotalol in rat plasma. Plasma samples were precipitated with acetonitrile before analysis. The chromatographic separation was performed on an Atlantis hydrophilic interaction liquid chromatography Silica column (50 × 2.1 mm, 3 µm) with a gradient mobile phase of 10 mm NH4 COOH (containing 0.2% of formic acid) as buffer A and acetonitrile as mobile phase B. Sotalol (m/z 273.2 → 255.1) and atenolol (the internal standard, IS, m/z 267.2 → 190.1) were monitored under positive ionization mode with 5500 QTRAP. Retention time of sotalol and the IS were 2.69 and 3.43 min, respectively. The linear range was 5-500 nm based on the analysis of 0.1 mL of plasma. The intrabatch precision ranged from 1.2 to 6.1%, and the inter-batch precision was from 3.3 to 6.5%. The coefficient of variation of IS-normalized matrix factor was 7.6%. Experiments for stability were performed and the analyte was sufficiently stable. A run time of 6 min for each injection made it possible to analyze a high throughput of plasma samples. The assay was successfully applied to the determination of sotalol in rat plasma after a micro-dose oral administration.

Bioluminescent sensor proteins for point-of-care therapeutic drug monitoring.

For many drugs, finding the balance between efficacy and toxicity requires monitoring their concentrations in the patient's blood. Quantifying drug levels at the bedside or at home would have advantages in terms of therapeutic outcome and convenience, but current techniques require the setting of a diagnostic laboratory. We have developed semisynthetic bioluminescent sensors that permit precise measurements of drug concentrations in patient samples by spotting minimal volumes on paper and recording the signal using a simple point-and-shoot camera. Our sensors have a modular design consisting of a protein-based and a synthetic part and can be engineered to selectively recognize a wide range of drugs, including immunosuppressants, antiepileptics, anticancer agents and antiarrhythmics. This low-cost point-of-care method could make therapies safer, increase the convenience of doctors and patients and make therapeutic drug monitoring available in regions with poor infrastructure.

Assessment of the appropriateness of serum digoxin concentration measurement in a medical group setting.

BACKGROUND: Recent quality initiatives require that the routine annual therapeutic drug-monitoring (TDM) parameters for the high-risk medication digoxin include a measure of renal function and a serum potassium level but not a serum digoxin concentration (SDC) measurement. Several studies have shown that the majority of the SDCs obtained in hospital settings provide little clinically actionable information. OBJECTIVE: To evaluate the appropriateness and utility of SDCs ordered in a medical group practice setting by categorizing the reason the SDC was ordered and identifying action taken in response to the result. METHODS: The descriptive study was conducted as a retrospective, electronic medical record (EMR) review of 90 primary care patients with continuous prescriptions for digoxin current on their medication profile with no gaps in therapy for at least 2 years prior to an SDC result entered into the EMR between January 1, 2009, and September 30, 2009. The reason the SDC was ordered was abstracted independently by 2 reviewers, who then assigned it to 1 of 8 predefined indication categories based on previously published criteria and practice guidelines. A third reviewer resolved inter-reviewer discrepancy (n = 1). RESULTS: A total of 90 patients with at least 1 SDC met inclusion criteria. Routine monitoring was the most frequent SDC order indication category with 35 patients (38.9%), 17 (48.6%) of whom did not have the recommended monitoring measures of potassium or renal function drawn concurrently. Patients were included in other categories as follows: confirmation of signs/symptoms of toxicity 30 (33.3%); assessment of factors altering pharmacokinetics 5 (5.6%); assessment of dosage change 5 (5.6%); assessment of drug interaction 3 (3.3%); assessment of clinical response 3 (3.3%); assessment of adherence 1 (1.1%); and other 2 (2.2%). Across all categories, a total of 19 (21.1%) of SDC results were outside the therapeutic range of 0.5 nanograms (ng) per mL and 2.0 ng per mL, 18 of which were below 0.5 ng per mL, with none of the subtherapeutic levels leading to a change in digoxin therapy. Only 1 patient (1.1%) had therapy changed in response to an elevated abnormal SDC result of 2.1 ng per mL and was in the routine monitoring category. CONCLUSIONS: The majority of SDC results obtained in our medical group setting did not lead to clinical action, such as dose adjustment or drug discontinuation. SDCs were commonly measured as part of routine monitoring, which is considered an inappropriate indication, and often without being accompanied by better markers for digoxin toxicity such as serum potassium levels and measures of renal function as recommended by drug-monitoring quality initiatives. Provider education is needed regarding the most indicative digoxin TDM parameters to obtain in order to satisfy quality initiatives.

Pharmacokinetics of ibutilide in patients with heart failure due to left ventricular systolic dysfunction.

STUDY OBJECTIVE: To assess whether the increased risk of ibutilide-induced torsade de pointes in patients with heart failure may be due to increased ibutilide exposure, we sought to determine if the pharmacokinetics of ibutilide are altered in patients with heart failure due to left ventricular systolic dysfunction. DESIGN: Multicenter, prospective pharmacokinetic study. SETTING: Four academic medical centers in the United States. PATIENTS: Sixteen adult patients with atrial fibrillation or atrial flutter requiring conversion to normal sinus rhythm: six patients who had New York Heart Association (NYHA) class II or III heart failure due to left ventricular dysfunction (mean +/- SD left ventricular ejection fraction [LVEF] 30 +/- 9%); 10 patients who did not have left ventricular dysfunction (mean +/- SD LVEF 54 +/- 5% in six of these 10 patients) served as controls. INTERVENTION: All patients received a single dose of ibutilide 1.0 mg administered intravenously over 10 minutes. Blood samples were obtained through an indwelling catheter in the contralateral arm before ibutilide administration, at the end of the infusion, and at 5, 15, 30, 45 minutes and 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 24, and 48 hours after the infusion. MEASUREMENTS AND MAIN RESULTS: Serum ibutilide concentrations were determined by using high-performance liquid chromatography and mass spectrometry. No significant differences were noted between the heart failure and normal left ventricular function groups in the following parameters: maximum serum ibutilide concentration (median [interquartile range] 3.8 [2.3-5.7] vs 5.8 [3.1-14.4] microg/L, p=0.31), area under the serum concentration-time curve from time zero extrapolated to infinity (mean +/- SD 11.0 +/- 9.4 vs 13.2 +/- 10.6 microg*hr/L, p=0.88), steady-state volume of distribution (1380 +/- 334 vs 1390 +/- 964 L, p=0.99), systemic clearance (129 +/- 60 vs 125 +/- 81 L/hr, p=0.92), or half-life (12.5 +/- 10.7 vs 12.4 +/- 8.6 hrs, p=0.99). CONCLUSION: The pharmacokinetics of ibutilide do not appear to be altered in patients with NYHA class II or III heart failure due to left ventricular systolic dysfunction. Therefore, the increased risk of ibutilide-induced torsade de pointes in patients with heart failure does not appear to be due to increased ibutilide exposure.

Assessment of serum flecainide trough levels in patients with tachyarrhythmia.

The reported therapeutic range for trough flecainide concentration is 200-1000 ng mL(-1). Severe adverse events, such as ventricular arrhythmias, have occurred occasionally in patients whose serum flecainide exceeded 1000 ng mL(-1). However, the lower limit remains controversial. We have evaluated blood flecainide concentrations in patients with tachyarrhythmia who received the drug to control palpitation. We measured the flecainide trough levels and incidence and frequency of palpitation of 44 outpatients receiving oral flecainide (150-300 mg daily). Mean serum flecainide trough concentrations differed significantly between patients with (n = 14) and without (n = 30) palpitation (259.5 +/- 85.2 vs 462.2 +/- 197.7 ng mL(-1), P < 0.01). The frequency of palpitation decreased as the serum flecainide concentration increased. The incidence of palpitation was 65% at serum flecainide concentrations < 300 ng mL(-1) and 11% at > or = 300 ng mL(-1). QRS values were increased significantly in patients with serum flecainide < 300 ng mL(-1) compared with > or = 300 ng mL(-1) (0.110 +/- 0.016 s vs 0.093 +/- 0.019 s, P < 0.05). We concluded that to control paroxysm in patients receiving flecainide for tachyarrhythmia serum flecainide concentrations should be maintained at > or = 300 ng mL(-1).

Derivation of occupational exposure limits based on target blood concentrations in humans.

An approach for deriving occupational exposure limits (OEL) for pharmaceutical compounds is the application of safety factors to the most appropriate pre-clinical toxicity endpoint or the lowest therapeutic dose (LTD) in humans. Use of this methodology can be limited when there are inadequate pre-clinical toxicity data or lack of a well-defined therapeutic dose, and does not include pharmacokinetic considerations. Although some methods have been developed that incorporate pharmacokinetics, these methods do not take into consideration variability in response. The purpose of this study was to investigate how application of compartmental pharmacokinetic modeling could be used to assist in the derivation of OELs based on target blood concentrations in humans. Quinidine was used as the sample compound for the development of this methodology though the intent was not to set an OEL for quinidine but rather to develop an alternative approach for the determination of OELs. The parameters for the model include body weight, breathing rate, and chemical-specific pharmacokinetic constants in humans, data typically available for pharmaceutical agents prior to large scale manufacturing. The model is used to simulate exposure concentrations that would result in levels below those that may result in any undesirable pharmacological effect, taking into account the variability in parameters through incorporation of Monte Carlo sampling. Application of this methodology may decrease some uncertainty that is inherent in default approaches by eliminating the use of safety factors and extrapolation from animals to humans. This methodology provides a biologically based approach by taking into consideration the pharmacokinetics in humans and reported therapeutic or toxic blood concentrations to guide in the selection of the internal dose-metric.

Altered metabolite concentrations with amiodarone generic substitution cannot be observed without monitoring.

The use of amiodarone has grown rapidly, resulting in the marketing of several generic formulations. The adequacy of the testing used to approve these formulations as bioequivalent has been questioned, and mounting clinical evidence suggests that in some patients, substitution with generic amiodarone can cause serious problems. The effects of switching amiodarone formulations may take weeks to develop, leaving the relationship between the events unrecognized. In animal models, the toxicity of desethylamiodarone, an active metabolite partly formed during amiodarone absorption, is greater than that of its parent compound. High metabolite to amiodarone ratios have been associated with clinical toxicity. Because measuring serum amiodarone and metabolite is not standard clinical practice, aberrations after switching formulations will be missed. Major changes in metabolite concentrations were documented in four patients switched to a generic formulation, suggesting that the tests used for regulatory approval failed to identify the cumulative effects of differing excipients on amiodarone metabolism during absorption. Physicians should monitor patients for several months after a switch in amiodarone formulation is made. Regulatory criteria for bioequivalence of amiodarone need to be reconsidered.

[Measurement of serum amiodarone by protein precipitation followed by high performance liquid chromatography with ultraviolet detection]. / Cuantificación de amiodarona en suero mediante precipitación de proteínas seguida de cromatografía liquida de alta resolución con detección ultravioleta.

Our aim was to develop a quantitative method for serum amiodarone measurement using high performance liquid chromatography with ultraviolet photometric detection. We studied previous reports in the literature in order to obtain a simpler method to be used routinely in our TDM unit. Sample preparation was based on protein precipitation adding 2 parts of acetonitrile to 1 part of serum, followed by vortex-agitation for 45 s, incubation at 24 degrees C for 5 min, and centrifugation at 6000 x g for 2 min. Twenty microliters of the supernatant was directly injected into the chromatographic system. A microBondapak CN RP column (3.9 x 150 mm) at 45 degrees C, with a mobile phase consisting of KH2PO4 10 mM/methanol/acetonitrile (40:37:23 v/v/v), pH 3.5, were used. Eluting with a flow rate of 0.6 mL/mm the retention time of amiodarone was approximately 4.9 min. Detection was performed at 242 nm and the quantification was made by peak height comparison with external standards. The mass/response ratio is linear (r2 > 0.99) within a mass range of 2.96 to 18,930 ng of injected amiodarone, which exceeds the requirements for the monitoring of serum levels (0.3 to 6.0 micrograms/mL). Sample storage should be done with acetonitrile-extracted sera at -16 degrees C to avoid degradation. The method is very efficient, linear, sensitive and specific but it also simpler and cheaper than others reported in the literature.

Cuantificacion de amiodarona en suero mediante precipitacion de proteinas seguida de cromatografia liquida de alta resolucion con deteccion ultravioleta / Measurement of serum amiodarone by protein precipitation followed by high performance liquid chromatography with ultraviolet detection

Nos propusimos desarrollar un método para la medición de amiodarona en suero mediante cromatografia líquida de alta resolución con detección ultravioleta, optimizando las condiciones analíticas descritas en la literatura y determinar las condiciones óptimas de almacenamiento de la muestra, para la instalación de un servicio nacional de referencia. la preparación de la muestra consistió en la adición de 2 partes de acetonitrilo a 1 parte de suero, agitación por 45s, incubación a 24§C por 5 min, centrifugación a 6000 x g durante 2 min e inyección de 20 mu L del sobrenadante al cromatógrafo. Utilizando una columna mu Bondapak CN RP (3.9 x 150 mm) a 45§C, con una fase móvil compuesta por KH2PO4 10 mM/metanol/acetonitrilo (40:37:223 v/v/v) a pH 3,5, bombeada a 0,6 mL/min, obtuvimos un tiempo de retención de 4,9 min. La detección se realizó a 242 nm, y la cuantificación mediante comparación con estándares externos; el límite de detección fue de 0,11 mu g/mL. La relación masa/respuesta fue lineal (r2 > 0,99) para inyecciones con masa nominal de 2,96 a 18930 ng, lo cual excede lo requerido para el monitoreo de amiodarona sérica (0,3 a 6,0 mu g/ml). La recuperación fue de 99,26 por ciento más o menos 2,84 por ciento. El almacenamiento a -16§C de muestras precipitadas evita la degradación de la droga. Este método resultó más eficiente, sencillo y económico que otros ya descritos, manteniendo la sensibilidad, especificidad y linealidad requeridas para ser considerado un método óptimo para la cuantificación de amiodarona en suero.

Comparison by external quality assessment of performance of analytical systems for measurement of therapeutic drugs in serum.

The precision and accuracy of analytical methods currently in use for therapeutic drug monitoring were evaluated from proficiency test data provided by laboratories participating in the international Healthcontrol external quality assessment scheme for a range of eight antiepileptic drugs, theophylline, caffeine, and digoxin. Different analytical systems were assessed after grouping according to the reagent source and the analyzer used. The majority of analytical methods produced comparable levels of performance with coefficient of variation of < 10% and accuracy within +/-7% of the spike value. Emit reagents were implemented successfully on diverse analyzers but data from the Cobas Mira were generally in the technique group with significantly lower precision. Bias problems were evident for a number of FPIA assays for specific drugs. For example, caffeine interference was present in theophylline measurements by Sigma FPIA reagents whereas use of nonhuman matrix caused a negative bias in Abbott FPIA measurements of carbamazepine. Measurements in the group with highest positive bias were produced by Roche FPIA reagents for phenytoin, phenobarbitone, and carbamazepine. Chromatographic and turbidimetric techniques performed satisfactorily. The variable performance of the different reagent/analyzer combinations demonstrates the value of the narrower technique classification in the assessment of assay performance.

Assessment of frequency dependency of the class III effects of almokalant: a study using programmed stimulation and recording of monophasic action potentials and ventricular paced QT intervals.

The aim of the present study was to assess the frequency dependency of the effects of almokalant, a selective class III antiarrhythmic drug, on ventricular repolarization using recordings of monophasic action potentials and measurements of ventricular paced QT intervals. Twenty male volunteers were studied during almokalant infusion aiming at plasma concentrations (Cpl) of 20, 50, 100, and 150 nmol/l. The duration of monophasic action potential at 90% repolarization (MAPD) was measured during incremental and premature ventricular extrastimulation. The ventricular paced QT interval was measured during incremental stimulation from the apical region (RV APEX) and the outflow tract (RVOT) of the right ventricle, and the frequency dependence was analyzed using a linear regression model. At an almokalant dose of Cpl > or = 50, there was a significant prolongation of the MAPD of 10-15%. The prolongation was of equal magnitude at all paced cycle lengths (CL). The MAPD of ventricular extrasystole increased in parallel over the range of coupling intervals studied and was significantly prolonged at Cpl 100 and 150. The ratio between the MAPD of the extrasystoles and preceding beats was unaltered after almokalant infusion. The ventricular paced QT intervals increased during almokalant infusion in a similar manner as that of the MAPD. During RV APEX stimulation, the prolongation was more pronounced at low heart rates, an effect that was not seen during RV OT stimulation. Almokalant significantly prolonged the MAPD at dose levels Cpl > or = 50. There was no evidence of a frequency dependence of this effect. The ventricular paced QT intervals were prolonged in a similar manner as that of the MAPD, and this effect exhibited a small reverse frequency dependence during RV APEX stimulation.

Short-term variability of ventricular arrhythmia and rapid assessment of drug efficacy.

Statistical criteria for suppression and aggravation of ventricular arrhythmia were defined by means of 50 short-term drug tests performed in 24 patients. Each patient's spontaneous variability (SV) was evaluated by linear regression analysis of hour-to-hour changes in ectopy during 24- to 48-hour Holter monitoring. The response to a single oral dose of disopyramide, 300 mg, flecainide, 200 mg, and propafenone, 450 mg, was measured during a trial lasting 4 hours. Lidocaine was administered intravenously in incremental doses of up to 4 mg/min and was evaluated over 3 hours. Threshold values of ventricular arrhythmia corresponding to 95% confidence limits were calculated from baseline recordings and were used to ascertain the likelihood of a true drug effect. The minimum decrease in hourly ectopy indicating arrhythmia suppression averaged 90.9%, while an increase of at least 947% was required for a proarrhythmic effect. When these efficacy criteria were applied, 16 of 50 short-term tests revealed no drug effect. In contrast, when a 70% threshold derived from studies of daily variability was employed, only 7 of 50 trials were negative. Thus individual determination of hourly arrhythmia variability yields more stringent criteria than extrapolation from day-to-day spontaneous variation.

EO-199, a specific antagonist of antiarrhythmic drugs: assessment by binding experiments and in vivo studies.

EO-199, a demethylated analog of the novel class I antiarrhythmic drug EO-122 was found to antagonize the antiarrhythmic activity of EO-122 and that of procainamide (Class IA). EO-199 did not block significantly the activity of a class IB antiarrhythmic agent, lidocaine. EO-199 also displaced the specific binding of [3H]EO-122 to rat heart membranes similarly to procainamide whereas lidocaine did not. The correlation between binding experiments and pharmacological effects points to a possible subclassification of these drugs; the two chemical analogs EO-199 and EO-122, as well as procainamide (IA) but not lidocaine (IB), compete at the same site or the same state of the sodium channel. The availability of a specific antagonist might be useful for studying the mechanism of action of antiarrhythmic drugs as well as an antidote in cases of antiarrhythmics overdose intoxication.

Simultaneous liquid-chromatographic determination of five antiarrhythmic drugs and their major active metabolites in serum.

We report an isocratic "high-performance" liquid chromatographic method for the simultaneous measurement of tocainide, lidocaine, procainamide, quinidine, disopyramide, and their major active metabolites in serum. The drugs are extracted from 200 microL of serum at pH 9.5 with 1.5 mL of 1,2-dichloromethane, concentrated by evaporation, and separated on a CN-bonded-phase column at 40 degrees C (flow rate 2 mL/min) with a pH 7.1 mobile phase of acetonitrile/methanol/phosphate buffer (60/7/33, by vol); the phosphate buffer contains 10 mmol of KH2PO4 and 0.5 mmol of triethylamine per liter. The antiarrhythmic drugs elute in the K' (capacity factor) range of 1.43 (lidocaine) to 5.7 (disopyramide). Results vary linearly with drug concentration to at least 30 mg/L; the detection limit is 0.1-0.2 mg/L. Within-run precision (CV) ranges from 0.9% to 5.0% and day-to-day precision from 2.1% to 6.2%, depending on the specific drug and its concentration in serum. Extraction efficiencies vary from 76% to 85% and analytical recoveries from 98.5% to 103%. At toxic serum concentrations, several basic drugs may interfere with the assay of some antiarrhythmics, but only hydroxyzine, verapamil, and certain local anesthetics interfere at therapeutic concentrations.

The assessment of antidysrhythmic drugs.

Assessments of efficacy of antidysrhythmic drugs at different clinical arrhythmia centers frequently produce discordant data, probably because of differences in patient population, technology to assess efficacy, study design, and concomitant drugs such as digitalis, diuretics, beta-adrenergic blocking agents, and calcium channel blockers. Furthermore, different doses employed may greatly influence the toxicity and efficacy of both conventional and experimental antiarrhythmic drugs. These variables make the design of studies in the field of antiarrhythmic therapy both difficult and of critical importance. The serious and complex nature of the disease entity against which these drugs are directed constitutes a considerable public health problem which requires that the problems be addressed in a definite and timely way.