Determination of unlabeled and 13C6-labeled moricizine in human plasma using thermospray liquid chromatography-mass spectrometry.

Moricizine hydrochloride is an orally effective antiarrhythmic agent currently marketed in the Soviet Union and undergoing clinical testing in the United States. To facilitate the simultaneous analysis of unlabeled and 13C6-labeled moricizine in human plasma, a specific and sensitive method employing liquid-liquid extraction followed by thermospray liquid chromatography-mass spectrometry (LC-MS) was developed. Plasma samples, after addition of [2H11]moricizine as an internal standard, were extracted into methylene chloride under alkaline conditions. Extracts were evaporated, reconstituted with mobile phase, and chromatographed on an ODS column. The LC mobile phase consisted of methanol-0.1 M ammonium acetate containing 0.2% triethylamine (65:35) and it was used at a flow-rate of 1.5 ml/min. Under these conditions, moricizine and [13C6]moricizine coeluted at 1.2 min, while [2H11]moricizine eluted slightly earlier. The MS system consisted of a Finnigan 4600 TSQ and a Vestec thermospray interface. Selected ions at m/z 428, 434, and 439 were scanned at 0.2 s per ion. Over a plasma concentration range of 10-800 ng/ml, intra-day precision (n = 3) ranged from 1.8 to 13.3% and intra-day accuracy ranged from 1.9 to 15.8%. This method was successfully used to assay human plasma samples from a pilot moricizine bioavailability study in which tablets and solution containing moricizine hydrochloride and [13C6]moricizine, respectively, were simultaneously administered.

Pharmacokinetics and metabolism of rimantadine hydrochloride in mice and dogs.

We studied the pharmacokinetics and metabolism of rimantadine hydrochloride (rimantadine) following single-dose oral and intravenous administration in mice and dogs. Absorption of the compound in mice was rapid. Maximum concentrations in plasma occurred at less than 0.5 h after oral administration, and the elimination half-life was 1.5 h. Peak concentrations in plasma following oral administration were markedly disproportional to the dose (274 ng/ml at 10 mg/kg, but 2,013 ng/ml at 40 mg/kg). The bioavailability after an oral dose of 40 mg/kg was 58.6%. Clearance was 4.3 liters/h per kg, and the volume of distribution was 7.6 liters/kg at 40 mg/kg. In contrast to the results observed in mice, absorption of the compound in dogs was slow. Maximum concentrations in plasma occurred at 1.7 h after oral administration, and the elimination half-life was 3.3 h. A further difference was that peak concentrations in plasma were approximately proportional to the dose. Following administration of a single oral dose of 5, 10, or 20 mg/kg, maximum concentrations in plasma were 275,800, and 1,950 ng/ml, respectively. The bioavailability after an oral dose of 5 mg/kg was 99.4%. The clearance was 3.7 liters/h per kg, and the volume of distribution was 13.8 liters/kg at 5 mg/kg. Mass balance studies in mice, using [methyl-14C]rimantadine, indicated that 98.7% of the administered dose could be recovered in 96 h. Less than 5% of the dose was recovered as the parent drug in dog urine within 48 h. Finally, gas chromatography-mass spectrometry studies, done with mouse plasma, identified the presence of two rimantadine metabolites. These appeared to be ring-substituted isomers of hydroxy-rimantadine.

Distribution of the novel anticancer drug candidate Brequinar sodium (DuP 785, NSC 368390) into normal and tumor tissues of nude mice bearing human colon carcinoma xenografts.

The distribution of the novel anticancer drug candidate Brequinar Sodium (DuP 785, NSC 368390) was studied in control mice and mice implanted subcutaneously with human colon carcinoma xenografts. Mice were given radiolabeled 14C-Brequinar Sodium intravenously. Brequinar concentrations in blood and various tissues were determined at 1, 6, and 24 h after drug administration. Within 1 h Brequinar distributed to the tumor and all other tissues studied. The tumor-to-blood drug concentration ratios ranged from 0.19 to 0.41. Radioactivity in the liver and small intestine at 1 h accounted for 17% and 13%, respectively, of the dose given. Elimination rates of Brequinar from all tissues were approximately equal to that from blood. Comparison of blood concentrations determined by both radioactivity and HPLC methods suggests that the intact drug is probably the only form in the blood.

The disposition and bioavailability of intravenous and oral nalbuphine in healthy volunteers.

The pharmacokinetics of intravenous and oral nalbuphine were studied in 24 healthy male volunteers ranging in age from 21 to 30 years. On separate test days over a five-week period, subjects received single doses of each of four different formulations of nalbuphine, with a one-week washout period between treatments: 10 mg intravenously administered over two minutes, 45 mg orally given as a solution, and 45 mg orally administered in two tablet formulations (formulation A and formulation B). Blood samples were collected over 48 hours postadministration, and plasma nalbuphine concentrations were determined by reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. The mean nalbuphine plasma concentration five minutes after 10 mg intravenously was 53 ng/mL, and the half-life of nalbuphine with this route of administration was 2.3 hours. In contrast, mean maximum nalbuphine concentrations (Cmax) after the three orally administered preparations ranged from 14.4 to 15.5 ng/mL, and occurred 0.9 to 1.2 hours after dose administration. Mean elimination half-lives after administration of the three nalbuphine oral formulations were essentially identical, ranging from 6.9 to 7.7 hours. Nalbuphine plasma concentration curves decayed biexponentially regardless of route of administration or type of formulation. Absolute bioavailability of the orally administered forms of nalbuphine ranged from 16.4 to 17.4% and Cmax and AUC data further established the bioequivalence of the three oral formulations. The low absolute bioavailability and prolonged elimination half-life of nalbuphine associated with oral administration are likely due to extensive first-pass metabolism and enterohepatic circulation, respectively.

The pharmacokinetics of intravenous, intramuscular, and subcutaneous nalbuphine in healthy subjects.

The pharmacokinetics of intravenously, intramuscularly, and subcutaneously administered nalbuphine were studied in three parallel groups of 12 healthy volunteers each. The subjects received single doses of 10 mg and 20 mg of nalbuphine separated by a one week washout period. Blood specimens were obtained up to 15 h after dosing for determination of nalbuphine. Mean plasma nalbuphine concentrations 5 min after intravenous administration of 10 or 20 mg were 39 and 73 ng/ml, respectively. The mean maximum plasma concentrations (Cmax) after intramuscular or subcutaneous administration of nalbuphine 10 mg were 29 and 31 ng/ml, respectively. Mean Cmax values after 20 mg doses were 60 and 56 ng/ml. Mean Cmax occurred 30 to 40 min after nalbuphine administration. The mean elimination half-lives of parenterally administered nalbuphine ranged between 2.2 and 2.6 h, regardless of dose given or route administered. The mean absolute bioavailability was 81% and 83% for the 10 and 20 mg intramuscular doses, respectively, and 79% and 76% following 10 and 20 mg of subcutaneous nalbuphine. The mean volumes of distribution (Vss) of the intravenously administered drug were 290 and 274 l and the mean systemic clearances were 1.6 and 1.5 l/min following administration of 10 and 20 mg doses, respectively. Intramuscular and subcutaneous nalbuphine appear to be interchangeable based on the similarities in Cmax, mean times until maximum concentration, mean AUC data, and absolute bioavailabilities.

Disposition of moracizine (ethmozine) in healthy subjects after oral administration of radiolabelled drug.

Moracizine (ethmozine) is a phenothiazine derivative with demonstrated antiarrhythmic activity. To characterize the pharmacokinetics and material balance relationships in humans, we have given 14C-moracizine X HCl as a single oral dose of 500 mg (50 microCi) to six healthy men. Plasma, urine, and faecal samples were collected for 7 days after administration and the concentrations of total radioactivity and intact moracizine were determined by liquid scintillation counting and HPLC, respectively. Urine and faecal recovery accounted for 95% of the administered radioactivity. Most of this radioactivity was found in the faeces (59%). Only 0.05% of the dose was recovered from urine as intact moracizine. The Cmax and AUC for moracizine equivalents of total radioactivity were 4- and 18-fold higher, respectively, than the corresponding values for intact moracizine. Additionally, both the disappearance of total radioactivity from plasma and its excretion rate into urine were slower in comparison to intact drug. Terminal t1/2 values calculated from plasma concentration-time data were 85.2 and 3.5 h for total radioactivity and intact moracizine, respectively. However, based on urinary excretion rates, the t1/2 for total radioactivity was shorter (29.3 h) while the t1/2 for intact drug was comparable (2.7 h) to the results obtained from the plasma data. The oral plasma clearance of moracizine was relatively large (2.2 l X min-1), suggesting first-pass metabolism. The estimated oral systemic availability of moracizine was 34%.

Mechanism of the pressor effect of the calcium agonist, BAY k 8644, in the intact rat.

The purported calcium agonist BAY k 8644 was tested as a pressor agent in pentobarbital anesthetized and conscious Sprague-Dawley rats. A dose of 10 micrograms/kg increased mean arterial blood pressure (MABP) by 47 +/- 3 mm Hg in anesthetized and 39 +/- 3 mm Hg in conscious rats. The calcium channel blockers nitrendipine or nisoldipine (180 micrograms/kg/h) blocked 62-84% of the pressor response of BAY k 8644 (p less than 0.001 from control responses). The alpha-adrenergic receptor antagonist phentolamine (400 micrograms/kg) failed to alter the Bay k 8644 induced pressor response either in the conscious or anesthetized state. Moreover, the thromboxane receptor antagonist, SQ-29,548 and the leukotriene D4 and E4 receptor antagonist LY-171,883 at doses that markedly block thromboxanes or leukotrienes, respectively, had no effect on the BAY k 8644 induced pressor response. Neither the angiotensin II receptor antagonist, saralasin nor an arginine vasopressin antagonist (AVP-A) modify the BAY k 8644 induced pressor response. Thus, BAY k 8644 appears to directly increase MABP in the rat by activation of calcium influx into vascular smooth muscle and/or cardiac muscle cells, probably without the action of any common secondary vasoconstrictor mediator.

Assessment of the potential pharmacokinetic interaction between digoxin and ethmozine.

The potential for a pharmacokinetic interaction between the investigational antiarrhythmic drug ethmozine (moricizine HCl, the generic name that is infrequently used in existing literature) and digoxin was evaluated in nine healthy male adults. Serum and urinary digoxin concentrations were measured by radioimmunoassay following intravenous digoxin administration before and during steady-state ethmozine dosing. Plasma ethmozine levels following a single oral dose were measured before and after a single intravenous dose of digoxin. A mean elimination half-life of 45.6 hours was determined for digoxin alone, compared to 43.1 hours in combination with ethmozine. Average values for digoxin systemic clearance, apparent volume of distribution, and renal clearance were 2.87 mL/min/kg, 11.3 L/kg, and 2.44 mL/min/kg, respectively for digoxin alone, compared to 3.01 mL/min/kg, 11.3 L/kg, and 2.64 mL/min/kg, respectively for digoxin with ethmozine. A mean half-life of 2.0 hours was determined for ethmozine alone, compared with 1.8 hours following a single intravenous dose of digoxin. No change was observed in the oral pharmacokinetics of ethmozine following a single intravenous dose of digoxin, as indicated by the area under the plasma concentration versus time curve, Cmax or Tmax. These findings suggest that no pharmacokinetic interaction occurs when single intravenous doses of digoxin are co-administered with multiple oral doses of ethmozine.

High-performance liquid chromatographic method for the determination of tiflamizole in plasma.

A sensitive, specific, high-performance liquid chromatographic procedure was developed for the measurement of plasma tiflamizole levels. Acidic plasma samples were extracted with three volumes of ether. The ether extracts were combined and evaporated to dryness. The residue was dissolved in acetonitrile, washed with hexane, and the acetonitrile was evaporated to dryness. The residue was dissolved in 0.5 mL of mobile phase consisting of acetonitrile and 0.007 M pH 3 sodium phosphate buffer (70:30, v/v) and then chromatographed on a octadecylsilane bonded microparticulate silica column. The assay is specific, precise, accurate, and can measure 10 ng of tiflamizole in 5 mL of plasma. The method was applied to human pharmacokinetic studies.

Bioequivalence, dose-proportionality, and pharmacokinetics of naltrexone after oral administration.

Healthy male volunteers (N = 24) participated in a four-way crossover study to compare the rate and extent of absorption of naltrexone after administration of 50 mg tablets as 50, 100, and 200 mg doses and a 10 mg/ml reference syrup. A high-performance liquid chromatographic method was employed to measure naltrexone and 6-beta-naltrexol in plasma and urine. Compared to the syrup, the 50 mg tablets were absorbed more slowly but equally well. There was excellent linearity between the administered dose and the area under the plasma concentration-time profile, as well as total urinary recovery of both drug and metabolite. The mean half-lives for naltrexone and beta-naltrexol were approximately 4 and 12 hours, respectively. The fraction of drug reaching the systemic circulation was estimated to be 5% of the administered dose because of extensive first-pass metabolism. Less than 1% of the dose was excreted in the urine as naltrexone after 48 hours, while 25% was recovered as unconjugated beta-naltrexol. The renal clearance of naltrexone and beta-naltrexol was approximately 127 ml/min and 283 ml/min, respectively. The total systemic clearance for naltrexone was approximately 94 L/hr.

Determination of nalbuphine in human plasma by automated high-performance liquid chromatography with electrochemical detection.

A sensitive plasma assay for the agonist/antagonist analgesic nalbuphine utilizing reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection is described. It involves extracting nalbuphine from plasma at pH 9 into an ethyl acetate/toluene/isopropanol mixture and then back extracting it into aqueous phosphoric acid. The extract is injected onto an octyl column using a solvent mixture of acetonitrile and phosphoric acid. Intra-day assay coefficients of variation (CV) ranged from 0.2 to 4.2% over a concentration range from 0.21 to 42 ng/ml. Nalbuphine extraction recovery exceeded 90% using 1 or 3 ml of plasma. No degradation of the drug in frozen plasma was observed after 18 weeks. The limit of detection is 0.1 ng/ml using 3 ml of plasma.

High-performance liquid chromatographic determination of ethmozin in plasma.

A sensitive, specific high-performance liquid chromatographic procedure was developed for the determination of plasma ethmozin levels. Basic plasma samples were partitioned with methylene chloride. The organic extract was washed with water and then evaporated to dryness under reduced pressure. The residue was redissolved in 0.2 ml of the mobile phase, consisting of hexane-tetrahydrofuran-methanol-water (66:27:6,30:0.7 v/v), and then chromatographed on a microporous silica column. With a variable-wavelength UV detector set at 268 nm, 10 ng of ethmozin/ml of plasma was measured. The utility of the method for human pharmacokinetic studies was demonstrated.