Human moricizine metabolism. II. Quantification and pharmacokinetics of plasma and urinary metabolites

1. The metabolism of moricizine.HCl was studied in 12 male volunteers dosed with 250 mg (300 microCi) 14C-radiolabelled drug. 2. Moricizine was biotransformed to many metabolites in humans (at least 35 plasma and 51 urine metabolites). 3. Urine and faecal combined mean (range) recovery accounted for 90.2% (73.4-101.6%) of the administered radioactivity, with most of the recovered radioactivity present in faeces (mean 58.4%; range 45.6-64.7%). Mean (range) urinary recovery was 31.8% (26.2-36.9%), with <1% of the dose recovered as intact moricizine, and no one metabolite accounting for >2.5% of the dose. 4. Total radioactivity (TR) plasma t1/2 was 85.2 h, while that for moricizine was 2.4 h. Mean half-lives for plasma metabolites ranged from 2.9 to 23.6 h. The largest portion (11%) of TR AUC (area under the plasma concentration-time curve) was attributed to 2amino-10-glucuronophenothiazine. Each of the other metabolites accounted for less of the TR AUC than parent drug except for two unidentified peaks which had comparable areas (approximately 5% of the total radioactivity area). 5. Two identified moricizine metabolites, 2-amino-10-(3-morpholinopropionyl) phenothiazine and ethyl [10-(3-aminopropionyl) phenothiazin-2-yl] carbamate, possess the structural characteristics proposed for class 1 anti-arrhythmic activity (pendant amine functionality) and have plasma half-lives 4-7-fold longer than moricizine.

Moricizine bioavailability via simultaneous, dual, stable isotope administration: bioequivalence implications

The relative bioavailability of a 200 mg film-coated tablet of [12C]moricizine.HCl in comparison to a 200 mg [13C6]moricizine.HCl oral solution was determined after simultaneous administration to 8 young healthy male subjects. Concentrations of [12C]moricizine.HCl and [13C6]moricizine.HCl were determined by thermospray liquid chromatography-mass spectrometry (LC-MS) using [2H11]moricizine.HCl as the internal standard. The mean absorption and disposition parameters of the tablet versus the solution were the following (%CV): maximum concentration, 0.83 (39%) versus 0.79 (39%) microgram/mL; time of maximum concentration, 0.81 (40%) versus 0.65 (28%) hours; area under the concentration-time curve (AUC), 1.58 (39%) versus 1.49 (37%) micrograms.h/mL; apparent oral clearance, 150.7 (52%) versus 158.1 (50%) L/h; and t1/2, 1.9 (42%) versus 1.9 (42%) hours. The AUC for the tablet averaged 106% of the solution, which likely reflects a greater first-pass effect with the oral solution. Partitioning sources of variation confirmed the low (< 6%) intrasubject coefficient of variation (cv epsilon) afforded via the single-period, dual-isotope design. In contrast, a previous study using the conventional two-period crossover design determined the cv epsilon about moricizine metrics to be in excess of 30%, resulting in classification of this drug as having highly variable absorption. The results of this study further illustrate the benefits of dual, stable isotopes to assess bioavailability and bioequivalence. This paradigm results in a reduction in experimental time and subject inconvenience and lower costs in comparison with the standard crossover study. Perhaps most important is the improved statistical power for the evaluation of bioavailability or bioequivalence in the absence of period and sequence effects that confound the assessment of intrasubject variation in the standard crossover design.

Simultaneous determination of moricizine and its sulphoxidation metabolites in biological fluids by high-performance liquid chromatography

A simultaneous assay for moricizine, its two sulphoxidation metabolites, moricizine sulphoxide and moricizine sulphone, using high-performance liquid chromatography (HPLC) is described. The drug and metabolites and clozapine (internal standard) in biological fluids were extracted using pentanesulphonic acid into diethyl ether. The ethereal extract was evaporated to dryness and the residue was redissolved in the mobile phase (methanol-water-triethylamine, 65:35:0.5, v/v). The analyses were performed on a microBondapak reversed-phase C18 column housed in a Waters Z-module, linked to a C18 pre-column, with a run-time of 12 min. The retention times were 2.7, 3.5, 6.2 and 9.7 min for moricizine sulphone, moricizine sulphoxide, moricizine and clozapine, respectively. The recovery of the compounds from plasma ranged from 89.9% for the sulphoxide to 98.1% for clozapine. The limits of detection of the assay for moricizine, moricizine sulphoxide and moricizine sulphone were 20, 10 and 5 ng/ml, respectively.

Moricizine concentration to guide arrhythmia treatment: with attention to elderly patients

To test the relationship between plasma moricizine concentration and the electrocardiogram (ECG) and arrhythmia suppression, 17 symptomatic cardiac patients with 30 or more ventricular premature complexes per hour were studied. Seven patients were mature adults, less than 60 years of age; and ten were elderly adults, more than 60 years of age. During steady-state moricizine therapy, patients had plasma moricizine concentration determined over a dosing interval, and had standard 12-lead ECG and a 24-hour ambulatory ECG recorded. The mean moricizine dose was 215 +/- 29 mg every 8 hours; mean maximal moricizine concentration was 1.4 +/- 0.84 micrograms/ml; and mean t1/2 beta was 1.5 +/- 0.7 hours. Baseline age-related differences were found, including prolonged electrocardiographic intervals (PR and QRS) (P < .05), increased ventricular arrhythmias (P < .05), and reduction in creatinine clearance (P < .05) in the elderly. Compared with pretreatment values, PR (P < .05) and QRS (P < .05) prolongation was observed, and was more marked in elderly patients. Over a dosing interval, there were dynamic changes on the ECG that paralleled plasma moricizine concentration; that is, peak and nadir intact moricizine concentration occurred simultaneously with ECG changes: QRS and JTc prolonged (P < .05), and PR prolongation approached significance (P = 0.09). Suppression of ventricular premature complexes of 80% or more occurred in 15 patients, and ventricular tachycardia was abolished in 10 of 12 patients. Probit analysis revealed that the therapeutic antiarrhythmic concentration ranged from 0.20 to 3.6 micrograms/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of hepatic disease on the disposition of moricizine in humans

The pharmacokinetics of moricizine and two of its metabolites, moricizine sulfoxide and phenothiazine-2-carbamic acid ethyl ester sulfoxide, were studied in healthy control subjects and in patients with chronic liver disease (cirrhosis). Moricizine disposition was significantly altered by hepatic cirrhosis. Compared to healthy subjects, the hepatic disease patients had an increased Cmax (59%), an increased t1/2 (141%), and a reduced plasma clearance (71%). Additionally, small but statistically significant increases were observed for tmax and the fraction of moricizine not bound to plasma proteins in patients with hepatic disease. The elimination of both moricizine metabolites was also altered by hepatic dysfunction as indicated by significantly prolonged terminal half-lives. Furthermore, there was a reduction in the conversion of moricizine to moricizine sulfoxide. Both hepatic blood flow and hepatic metabolizing capacity were assessed in all subjects and patients by administration of indocyanine green and antipyrine, respectively. Indocyanine green and antipyrine plasma clearances were decreased by 38 and 51%, respectively, indicating that both functions were diminished by hepatic cirrhosis. We conclude that the moricizine dose required for arrhythmia patients with hepatic disease should be lower, and perhaps, the dosing frequency should be less than in patients with normal liver function.

Enzyme induction by moricizine: time course and extent in healthy subjects

Moricizine.HCl, a novel phenothiazine derivative with oral antiarrhythmic activity, was examined for its potential to induce its own hepatic metabolism and to alter the pharmacokinetics of the test substrate, antipyrine, in 12 healthy male subjects. Antipyrine oral clearance increased from a starting value of .74 mL/minute/kg to .98 (+32%, P < .01) after 7 days of moricizine administration (250 mg every 8 hours) and to 1.15 mL/minute/kg after 14 days (+47%, P < .05); t1/2 was correspondingly reduced. Moricizine oral clearance increased from a baseline of 3.01 L/hour/kg to 3.62 (+20%, P < .05) after 6 days of oral moricizine and 4.66 (+51%, not significant) after 13 days. Moricizine t1/2 was marginally, but consistently, increased (+23%, P < .05) instead of decreased as one would expect because of enzyme induction, presumably due to a decrease in systemic bioavailability and its influence on the oral volume of distribution. In half of the subjects who discontinued moricizine after 7 days, antipyrine pharmacokinetic values returned to near baseline 7 days later. Although moricizine was able to induce its own hepatic metabolism and that of antipyrine after 6 or 7 days of continuous administration, the electrocardiographic properties of moricizine did not appear to be altered by continuous dosing.

Defibrillation energy requirements during moricizine and moricizine-lidocaine therapy

Defibrillation energy requirements may be altered by antiarrhythmic agents. We investigated the effects of moricizine on the defibrillation threshold (DFT) in 18 pentobarbital-anesthetized pigs. The animals were randomized, in a blinded fashion, to moricizine or control (0.9% saline) treatment groups. Each group underwent three treatment phases: baseline, drug infusion (moricizine or saline), and drug infusion combined with lidocaine. Moricizine (2 mg/kg loading dose, 1.5 mg/kg/h infusion) and lidocaine (5 mg/kg loading dose, 4 mg/kg/h infusion) were dosed to achieve therapeutic concentrations. After 5 s of induced ventricular fibrillation, defibrillation was performed using a cardiac defibrillator interfaced with two epicardial electrode patches. DFTs were determined at baseline, during the drug phase, and during the combination of lidocaine with moricizine or saline. DFT values in the animals randomized to the control group were 15.2 +/- 4.2, 14.0 +/- 3.3, and 17.8 +/- 8.7 J at baseline, saline infusion, and saline combined with lidocaine, respectively. No significant differences were observed among the treatment phases. DFT values in the animals randomized to moricizine group were 12.1 +/- 2.8, 13.8 +/- 5.2, and 22.9 +/- 7.1 J at baseline, moricizine infusion, and moricizine combined with lidocaine, respectively. The DFT values during the lidocaine-moricizine combination treatment phase were significantly greater than baseline and moricizine alone (p < 0.002). The mean change in the DFT from baseline to moricizine (14% increase) was significantly different than the mean change in the DFT from baseline to saline (8% decrease) (p = 0.03). Lidocaine added to moricizine increased the DFT by 84%, which was significantly different from the 27% increase in the DFT when lidocaine was added to saline (p = 0.02). We conclude that moricizine minimally increases the DFT, but the combination of moricizine with lidocaine results in a synergistic rise in the DFT that may have detrimental clinical implications.

Characterization of the rate-dependent effects of ethmozine on conduction, in vivo, and on the sodium current, in vitro, in the newborn heart

We evaluated the effects of ethmozine on resting conduction intervals, myocardial refractory periods and His-Purkinje and intraventricular conduction in vivo in 11 neonatal dogs aged 7 to 16 days. Ethmozine produced significant prolongation in resting sinus cycle length (P < .05), in the atrioventricular nodal (P < .001) and His-Purkinje conduction time (P < .01) intervals and in the QRS duration (P < .01). Ventricular, but not atrial refractory periods were significantly prolonged (P < .05). Rate-dependent changes in His-Purkinje and intraventricular conduction were demonstrated after ethmozine by direct pacing of the bundle of His and right ventricular pacing. The development of steady-state conduction delay at a paced cycle length of 200 msec was characterized by a time constant (tau on) of 23.5 beats. The time constant of diastolic recovery (tau off) from rate-dependent conduction delay, determined during His bundle extrastimulation, was 171 msec. Ethmozine was highly proarrhythmic. A total of 7 arrhythmias were induced in 6 out of 12 neonates after administration of ethmozine. We also characterized ethmozine block of cardiac sodium channels in isolated neonatal canine ventricular myocytes using the whole cell variation of the patch clamp technique. Ethmozine (1.3-40 microM) produced a use-dependent block of cardiac Na channels that was dependent upon both drug concentration and pulse duration. Drug binding to inactivated channel states accounted for the observed use-dependent block. The time constant of recovery from use-dependent block ranged between 10 and 30 sec at 16 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of food on the oral absorption and bioavailability of moricizine

Moricizine, a unique Class I antiarrhythmic agent, was orally administered with and without a meal to 24 healthy male subjects to determine the effect of food on moricizine absorption and bioavailability. Relative to the fasting state, a standardized breakfast delayed the time to peak plasma moricizine concentration (1.2 vs. 0.9 hr; P less than .03) and lowered peak plasma moricizine concentration by 24% (0.55 vs. 0.72 microgram/mL; P less than .03). Bioavailability, as measured by area under the plasma moricizine concentration versus time curve, was not significantly altered by the meal.

Time course of moricizine's effect on signal-averaged and 12 lead electrocardiograms: insights into mechanism of action

The mechanism of action of moricizine, a new antiarrhythmic agent used in the Cardiac Arrhythmia Suppression Trial, is incompletely characterized. In addition, because moricizine is extensively metabolized, plasma moricizine concentration has an unknown relation to myocardial drug effect. Signal-averaged and standard electrocardiograms (ECGs) were used to monitor moricizine's myocardial effects in 16 patients with frequent ventricular premature complexes taking 600 to 900 mg daily. Three signal-averaged ECG variables were measured: total filtered QRS duration (fQRS), root-mean-square voltage in the terminal 40 ms of the QRS complex (V40) and the terminal low amplitude duration less than 40 microV (LAS). At steady state, plasma samples were collected and serial recordings of signal-averaged and standard ECGs were taken at 0, 1, 2, 4, 6 and 8 h after moricizine administration. A 24 h ambulatory ECG was recorded throughout the test period. Moricizine prolonged the fQRS (p less than 0.05) and decreased the V40 (p less than 0.05) of the signal-averaged ECG and prolonged the QRS (p less than 0.05) and corrected JT (JTc) intervals (p less than 0.05) of the standard ECG. The time course of the signal-averaged and standard ECG variables paralleled plasma moricizine concentration; that is, the maximal changes occurred at 1 to 2 h and declined to time 0 values at 8 h. The maximal changes were: fQRS (+8%), V40 (-33%), QRS (+8%) and JTc (+4%). Thus, dynamic changes were observed for intraventricular conduction (fQRS, QRS) and ventricular repolarization (JTc) over the dosing interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose proportionality of moricizine after escalating multiple doses in healthy volunteers

This study was designed to determine the dose linearity and proportionality of moricizine after multiple-dose administrations of 450 to 900 mg/day. The study design was an open-label, four-treatment, four-period sequentials escalating dose. Twelve subjects each received multiple doses of 150, 200, 250, and 300 mg of moricizine every 8 hours during 7 days of treatment. Blood samples for pharmacokinetic determinations were obtained on day 7 of each treatment period during an 8-hour time interval. Cmin determinations were also made on specific days of each treatment period. The AUC tau (area under the curve from time 0 to 8 hours), Cmax, and Cmin parameters were all normalized to the 250-mg (750 mg/day) dose. No statistically significant differences were seen in these parameters at the four treatment levels. It was concluded that moricizine follows first-order or linear pharmacokinetics after multiple dosing and exhibits dose proportional pharmacokinetics in the dosage-range studies. This range corresponds to the clinically useful dosage range.