Small blood volumes from children for quantitative sotalol determination using high-performance liquid chromatography

Development of a validated spectrofluorimetric method for assay of sotalol hydrochloride in tablets and human plasma: application for stability-indicating studies

The native fluorescence of sotalol hydrochloride (SOT) was used as a basis for establishing a new method of analysis for SOT in tablets and spiked human plasma. The fluorescence of SOT in water was measured at 310 nm when excited at 235 nm. The detection limit (LOD) was 0.37 ng/mL and the quantification limit (LOQ) was 1.08 ng/mL. The proposed method offers high sensitivity which permits determination of SOT, even if present in a very small amount, in human plasma. The obtained results were successfully compared to that of a reference pharmacopeial method and statistical analysis proved a good agreement between the results of both methods. Further investigation of the SOT stability upon exposure to various stress conditions, such as acidic, alkaline, oxidative and photolytic degradation conditions was also performed. The kinetics of acidic, alkaline and oxidative degradation of the drug showed a pseudo first order degradation reaction. A proposal of the degradation pathway was suggested and confirmed by developing a thin layer chromatographic method used for separation of SOT and its acidic and alkaline degradation products.

A multi-walled carbon nanotube-based magnetic molecularly imprinted polymer as a highly selective sorbent for ultrasonic-assisted dispersive solid-phase microextraction of sotalol in biological fluids

A modified multiwalled carbon nanotube-based magnetic molecularly imprinted polymer (MWCNT-MMIP) was synthesized and applied for selective extraction and preconcentration of sotalol (SOT) in biological fluid samples by using ultrasonic-assisted dispersive solid-phase microextraction (UA-DSPME).

Development of a gradient HPLC method for the simultaneous determination of sotalol and sorbate in oral liquid preparations using solid core stationary phase

A selective and sensitive gradient HPLC-UV method for quantification of sotalol hydrochloride and potassium sorbate in five types of oral liquid preparations was developed and fully validated. The separation of an active substance sotalol hydrochloride, potassium sorbate (antimicrobial agent), and other substances (for taste and smell correction, etc.) was performed using an Ascentis Express C18 (100 × 4.6 mm, particles 2.7 μm) solid core HPLC column. Linear gradient elution mode with a flow rate of 1.3 mL min(-1) was used, and the injection volume was 5 µL. The UV/Vis absorbance detector was set to a wavelength of 237 nm, and the column oven was conditioned at 25°C. A sodium dihydrogen phosphate dihydrate solution (pH 2.5; 17.7 mM) was used as the mobile phase buffer. The total analysis time was 4.5 min (+2.5 min for reequilibration). The method was successfully employed in a stability evaluation of the developed formulations, which are now already being used in the therapy of arrhythmias in pediatric patients; the method is also suitable for general quality control, that is, not only just for extemporaneous preparations containing the mentioned substances.

QT-RR relationships and suitable QT correction formulas for halothane-anesthetized dogs

Several QT correction (QTc) formulas have been used for assessing the QT liability of drugs. However, they are known to under- and over-correct the QT interval and tend to be specific to species and experimental conditions. The purpose of this study was to determine a suitable formula for halothane-anesthetized dogs highly sensitive to drug-induced QT interval prolongation. Twenty dogs were anesthetized with 1.5% halothane and the relationship between the QT and RR intervals were obtained by changing the heart rate under atrial pacing conditions. The QT interval was corrected for the RR interval by applying 4 published formulas (Bazett, Fridericia, Van de Water, and Matsunaga); Fridericia's formula (QTcF = QT/RR(0.33)) showed the least slope and lowest R(2) value for the linear regression of QTc intervals against RR intervals, indicating that it dissociated changes in heart rate most effectively. An optimized formula (QTcX = QT/RR(0.3879)) is defined by analysis of covariance and represents a correction algorithm superior to Fridericia's formula. For both Fridericia's and the optimized formula, QT-prolonging drugs (d,l-sotalol, astemizole) showed QTc interval prolongation. A non-QT-prolonging drug (d,l-propranolol) failed to prolong the QTc interval. In addition, drug-induced changes in QTcF and QTcX intervals were highly correlated with those of the QT interval paced at a cycle length of 500 msec. These findings suggest that Fridericia's and the optimized formula, although the optimized is a little bit better, are suitable for correcting the QT interval in halothane-anesthetized dogs and help to evaluate the potential QT prolongation of drugs with high accuracy.

Effect of Rifampicin on the Pharmacokinetics of Atenolol

Also poorly metabolized drugs, including certain beta-blocking agents, can be susceptible to drug interactions caused by transporter inhibitors and inducers. Thus, our aim was to investigate the effect of rifampicin on the pharmacokinetics of atenolol in healthy people. In a randomized cross-over study with two phases, nine healthy volunteers received a 5-day pretreatment with rifampicin (600 mg daily) or placebo. On day 6, a single 100 mg dose of atenolol was administered orally. The plasma concentrations of atenolol and its excretion into urine were measured up to 33 hr after dosing. Systolic and diastolic blood pressures and heart rate were recorded in a sitting position before the intake of atenolol and 2, 4, 6, and 10 hr later. During the rifampicin phase, the mean area under the plasma concentration-time curve (AUC(0-infinity)) of atenolol was decreased to 81% and renal clearance increased to 109% of the placebo phase values (P<0.05). Rifampicin pretreatment reduced, albeit not statistically significantly, also the peak plasma concentration (Cmax), AUC(0-33 hr), and amount of atenolol excreted to 85% (P=0.139), 81% (P=0.053), and 86% (P=0.12) of the respective placebo phase values. The average heart rate and diastolic blood pressure were slightly higher during the rifampicin phase compared with the placebo phase (P<0.05). To conclude, although the inducing effect of rifampicin may not have been at its maximum by day 6, rifampicin has only a minor effect on the pharmacokinetics of atenolol evidenced by a slight reduction in its bioavailability.

Development an ion-pair liquid chromatographic method for determination of sotalol in plasma using a monolithic column

A rapid and sensitive ion-pair HPLC method using a monolithic column and fluorescence detection has been developed for quantification of sotalol in plasma. The assay enables the measurement of sotalol for therapeutic drug monitoring with a minimum quantification limit of 10 ng ml(-1). The analytical method involves simple, one-step protein precipitation and no extraction procedure is needed. Sample preparation is fast and the analytical recovery was complete. The separation was carried out in reversed-phase conditions using a Chromolith Performance (RP-18e, 100 mm x 4.6 mm) column at ambient temperature. The mobile phase was 10% acetonitrile, 0.001 M heptane sulfonic acid, 0.02 M sodium dihydrogen phosphate, and distilled water to 100%, adjusted to pH 5.5 at a flow rate of 1.8 ml/min. The excitation wavelength was set at 235 nm, emission at 300 nm. The calibration curve was linear over the concentration range 20-1500 ng ml(-1). The coefficients of variation for inter-day and intra-day assay were found to be less than 7%. The method has been applied to the determination of sotalol in plasma from 12 subjects dosed with racemic sotalol.

Development of a safe and effective pediatric dosing regimen for sotalol based on population pharmacokinetics and pharmacodynamics in children with supraventricular tachycardia

OBJECTIVES

The objective of this study was to develop age-specific dosage guidelines for sotalol in children with supraventricular tachycardia (SVT) based on a population pharmacokinetic covariate analysis, clinical trial simulations, and pharmacodynamics.

BACKGROUND

A rapid onset of an effective and safe antiarrhythmic sotalol therapy, especially for infants and neonates, is frequently delayed because of age-dependent interpatient variability in pharmacokinetics and pharmacodynamics.

METHODS

Pediatric patients with SVT (mean age 3.51 years [range 0.03 to 17 years]) were analyzed after oral sotalol doses of 1.0 to 9.9 mg/kg/day using population pharmacokinetic analysis and clinical trial simulation (n = 76), pharmacokinetic/pharmacodynamic modeling for QT interval prolongation (n = 32), and for the concentration-antiarrhythmic-response relationship (n = 15).

RESULTS

Inter-individual differences in oral clearance and volume of distribution could largely be attributed to size and weight differences, with an additional age effect on clearance in children younger than one year. Neonates showed a higher sensitivity toward QTc interval prolongation compared with older patients. In a subgroup of 15 patients, one-half of the patients converted into sinus rhythm at sotalol trough levels of 0.4 mug/ml and more than 95% at 1.0 mug/ml. Dosing recommendations derived for different age groups based on these findings were starting dose and target dose of 2 and 4 mg/kg/day for neonates, 3 and 6 mg/kg/day for infants and children <6 years, and 2 and 4 mg/kg/day for children >6 years.

CONCLUSIONS

This study provides an example for rational drug dosage in children that copes with interpatient variability and can be easily switched to an individually guided therapy based on effective sotalol trough levels.

Effect of Itraconazole on the Pharmacokinetics of Atenolol

Our objective was to evaluate the effect of itraconazole on the pharmacokinetics of atenolol in healthy volunteers. In a randomized cross-over study with two phases, 10 healthy volunteers had 200 mg itraconazole orally or placebo for 2 days b.i.d., and in the morning of day 3, one hour after the last ingestion of itraconazole or placebo, each subject received 50 mg atenolol. The plasma concentrations of atenolol and its excretion into urine were measured up to 33 hr. Blood pressures and heart rate were recorded up to 10 hr. Itraconazole had no statistically significant effect on any of the pharmacokinetic or pharmacodynamic variables of atenolol. If anything, itraconazole increased the area under the plasma concentration-time curve (+12%; P = 0.159), peak plasma concentration (+19%; P = 0.165), and amount of atenolol excreted into urine (+13%; P = 0.166) suggesting a slight increase of atenolol bioavailability. It can be concluded that itraconazole does not have a clinically relevant effect on the pharmacokinetics of atenolol.

Development of an intravenous microdialysis method for pharmacokinetic investigations in humans

INTRODUCTION

Limited blood volume is a major problem in pharmacokinetic investigations in specific populations, e.g. children. Intravenous microdialysis might help to obtain improved data sets as it is already successfully done in small animals. Since quantification of drugs is crucial in microdialysis, we developed an in vitro method to produce a workable intravenous microdialysis for human use.

METHODS

A specifically designed microdialysis cell consisting of glass was heated to 37 degrees C. The cell was filled with Ringer's solution, plasma or whole blood. A microdialysis probe was inserted into the cell and perfused with Ringer's solution with addition of 4% dextran. The beta-receptor blocker sotalol served as a test drug. The stepwise in vitro evaluation process addressed issues of loss of dialysate, calibration by retrodialysis and relative recovery. These conditions were then applied in an in vivo pilot study to one single healthy volunteer after written informed consent.

RESULTS

To address loss of perfusion fluid 4% of dextran was added and high and constant amounts of dialysate were achieved. To account for changes in the relative recovery a continuous use of retrodialysis by the calibrator atenolol was introduced. The recovery of atenolol was comparable to sotalol. The pharmacokinetic analysis revealed that sotalol concentrations from microdialysates were not different from conventional plasma samples (100+/-11%, n=33) resulting in subsequent comparable pharmacokinetic parameters.

DISCUSSION

This stepwise approach using an in vitro device enabled us to demonstrate the determination of pharmacokinetic parameters of sotalol. The most important evaluation step is represented by the continuous use of retrodialysis by the calibrator atenolol because it can account for changes in the relative recovery of the drug. This approach should be a starting point to simplify pharmacokinetic studies in special populations, e.g. in small children, to improve drug treatment.

Effects of orange juice on the pharmacokinetics of atenolol

OBJECTIVE

Fruit juices can significantly change the pharmacokinetics of several drugs. Our objective was to investigate the effect of orange juice on the pharmacokinetics of the beta-blocking agent atenolol.

METHODS

In a randomized cross-over study with two phases and a washout of 2 weeks, ten healthy volunteers took either 200 ml orange juice or water thrice daily for 3 days and twice on the fourth day. On the morning of day 3, each subject ingested 50 mg atenolol with an additional amount of either 200 ml orange juice or water. The plasma concentrations of atenolol and the cumulative excretion of atenolol into urine were measured up to 33 h after its dosing. Systolic and diastolic blood pressures and heart rate were recorded in a sitting position before the intake of atenolol and 2, 4, 6, and 10 h after.

RESULTS

Orange juice decreased the mean peak plasma concentration (C(max)) of atenolol by 49% (range 16-59%, P<0.01), and the mean area under the plasma atenolol concentration-time curve (AUC(0-33 h)) by 40% (range 25-55%, P<0.01). The time of the peak concentration (t(max)) and the elimination half-life (t(1/2)) of atenolol remained unchanged by orange juice. The amount of atenolol excreted into urine was decreased by 38% (range 17-60%, P<0.01), but the renal clearance remained unaltered. The average heart rate was slightly higher during the orange juice+atenolol phase than during the water+atenolol phase.

CONCLUSIONS

Orange juice moderately interferes with the gastrointestinal absorption of atenolol. This food-drug interaction can be of clinical significance.

HPLC quantification of metoprolol with solid-phase extraction for the drug monitoring of pediatric patients

Although the analytical literature seems abundant for the determination of metoprolol in human plasma, a method using standard equipment providing a sensitive and simple high-performance liquid chromatographic (HPLC) method for limited blood volume, e.g. where 1 mL of blood in a 1 kg infant equals 70 mL of adult blood volume, has rarely been addressed. Therefore, in 500 microL of plasma, metoprolol was extracted using an internal standard and solid-phase extraction columns. Chromatographic analysis was performed on a Spherisorb C(6) column (5 microm particle size) at ambient temperature and fluorimetric detection with an excitation wavelength of 225 nm, and emission wavelength of 310 nm. The mobile phase [30% acetonitrile and 70% 0.25 m potassium acetate buffer (pH 4)] was pumped with 1 mL/min. Metoprolol recovery was determined at 73.0 +/- 20.5%, and the limit of quantitation was 2.4 ng/mL. Precision values of intra- and inter-assay were below 15.5% and those for accuracy were between 90 and 110%. This method was developed for monitoring and determination of pharmacokinetic parameters of metoprolol in pediatric patients and therefore metoprolol plasma concentrations in a 2-year-old child with ventricular tachycardia are reported. .

Carvedilol but not metoprolol reduces beta-adrenergic responsiveness after complete elimination from plasma in vivo

BACKGROUND

Carvedilol but not metoprolol exhibits persistent binding to beta-adrenergic receptors (beta-ARs) even after washout in cell culture experiments. Here, we determined the significance of this phenomenon on human beta-ARs in vitro and in vivo.

METHODS AND RESULTS

Experiments were conducted on human atrial trabeculae (n=8 to 10 per group). In the presence of metoprolol, isoproterenol potency was reduced compared with controls (P<0.001). In the presence of carvedilol, isoproterenol identified 2 distinct binding sites of high (36+/-6%; -8.8+/-0.4 log mol/L) and low affinity (-6.5+/-0.2 log mol/L). After beta-blocker washout, isoproterenol potency returned to control values in metoprolol-treated muscles, whereas in carvedilol-treated preparations, isoproterenol potency remained decreased (P<0.001 versus control). In vivo studies were performed in 9 individuals receiving metoprolol succinate (190 mg/d) or carvedilol (50 mg/d) for 11 days in a randomized crossover design. Dobutamine stress echocardiography (5 to 40 microg x kg(-1) x min(-1)) was performed before, during, and 44 hours after application of study medication. Beta-blocker medication reduced heart rate, heart rate-corrected velocity of circumferential fiber shortening, and cardiac output compared with baseline (P<0.02 to 0.0001). After withdrawal of metoprolol, all parameters returned to baseline values, whereas after carvedilol, all parameters remained reduced (P<0.05 to 0.001) despite complete plasma elimination of carvedilol.

CONCLUSIONS

Carvedilol but not metoprolol inhibits the catecholamine response of the human heart beyond its plasma elimination. The persistent beta-blockade by carvedilol may be explained by binding of carvedilol to an allosteric site of beta-ARs.

Fully automated LC method for the determination of sotalol in human plasma using restricted access material with cation exchange properties for sample clean-up

A simple and rapid fully automated bio-analytical method for the liquid chromatographic (LC) determination of sotalol in human plasma has been described. The method is based on the use of a new kind of porous silica restricted access material (RAM) with cation exchange properties for sample clean-up. 100 microl of plasma samples were directly injected into the precolumn coupled on-line to a reversed-phase column (RP-Select B) by means of column switching system. The plasma matrix was washed out for 10 min using a washing liquid composed of 2 mM lithium perchlorate and methanol (97:3; v/v). By rotation of the switching valve, the analytes were then eluted in back-flush mode for 2 min and transferred to the analytical column by the LC mobile phase constituted of a mixture of methanol and 50 mM potassium phosphate buffer (pH 7.0) containing 1 mM 1-octanesulphonic acid sodium salt (20:80; v/v). The flow-rate was 1.0 ml/min and sotalol was detected using fluorescence detection at 235 and 300 nm as excitation and emission wavelengths, respectively. The method was then validated using a new approach based on accuracy profile over a concentration range from 5 to 500 ng/ml. The limit of quantitation (LOQ) was 5 ng/ml and the total analysis time was 19 min.

Enantioselective determination of (R)- and (S)-sotalol in human plasma by on-line coupling of a restricted-access material precolumn to a cellobiohydrolase I-based chiral stationary phase

A liquid chromatographic column-switching method for the enantioselective determination of (RS)-sotalol in plasma was developed and validated. The method is based on the on-line coupling of a precolumn filled with the restricted access material LiChrospher ADS to a cellobiohydrolase I-based chiral stationary phase (CSP). The plasma samples were injected onto the precolumn using a mobile phase containing 1% methanol in 10 mM phosphate buffer at pH 7.4 for 10 min for the removal of matrix components. The analytes were transferred to the CSP for their enantiomeric separation by backflushing the precolumn with 15% 2-propanol in 10 mM phosphate buffer (pH 7.0) including 0.05 mM EDTA. The quantitative determination of the sotalol enantiomers was possible upon addition of the internal standard (S)-atenolol. The method was validated showing a good linearity in the concentration range from 25 to 1000 microg l(-1) for each enantiomer. The average values of the intra- and inter-day variability were 1.17% and 3.42%, respectively, for (R)-sotalol and 1.24% and 1.99%, respectively, for (S)-sotalol. The applicability of the method to real world samples has been proven by means of two pharmacokinetic studies. They revealed that the pharmacokinetic properties of the sotalol enantiomers do not differ significantly neither for healthy young volunteers after single dose application nor for elder patients in the steady state.

Simultaneous determination of eight beta-blockers by gradient high-performance liquid chromatography with combined ultraviolet and fluorescence detection in corneal permeability studies in vitro

A gradient HPLC method with combined ultraviolet and fluorescence detection was developed for the simultaneous determination of eight beta-blockers (alprenolol, atenolol, metoprolol, nadolol, pindolol, propranolol, sotalol and timolol) in corneal permeability studies in vitro. Fluorescence detection with excitation wavelength at 230 nm and emission at 302 nm was selective for six of the compounds, whereas UV detection at 205 nm was able to detect all the compounds. Calibration was performed with fluorescence detection for six compounds from 50 or 200 nM to 3 microM, and with UV detection for all the eight compounds from 100 or 200 nM to 30 microM. With optimized fluorescence detection, detection limits between 0.7 and 1.3 nM (0.035-0.065 pmol per 50 microl injection) were obtained for atenolol, metoprolol, nadolol and sotalol. A mixture of eight beta-blockers was used in cassette dosing permeability studies with a cultured corneal epithelium. The HPLC method revealed marked differences in the permeation between hydrophilic and lipophilic beta-blockers through the corneal epithelial cell culture model.