Henry J. Pieniaszek

Variability in the Pharmacokinetics and Pharmacodynamics of Low Dose Aspirin in Healthy Male Volunteers

Data describing the pharmacokinetics and pharmacodynamics of low dose aspirin (acetylsalicylic acid; ASA) are limited. This single‐center study was designed to determine the rate and extent of oral absorption of 80‐mg ASA tablets in healthy, young male subjects and to assess the intra‐ and inter‐subject variability of ASA pharmacokinetics and platelet aggregation effects. Ten subjects each received a single, open‐label, oral 80‐mg ASA dose on three separate days. Each dose was separated by a 2‐week washout interval. Blood samples for pharmacokinetic determinations of ASA and its metabolite, salicylic acid (SA) and platelet aggregation studies were obtained at scheduled timepoints before and up to 24 hours after each dose. Peak plasma ASA levels of 1 μg/mL were achieved within 30 minutes. Peak plasma SA levels of approximately 4 μg/mL were attained in 1 hour. The terminal half‐lives (t1/2) of ASA and SA were 0.4 and 2.1 hours, respectively. Both ASA and SA pharmacokinetics and the platelet aggregation response to ASA exhibited considerable intra‐ and inter‐subject variability. Inhibition of platelet aggregation was found to relate with ASA area under the plasma concentration versus time curve (AUC).

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 toa200 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%) μg/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%) μg•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 (cvε) afforded via the single‐period, dual‐isotope design. In contrast, a previous study using the conventional two‐period crossover design determined the cvε 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.

Oxymorphone extended release does not affect CYP2C9 or CYP3A4 metabolic pathways

Two 14‐day, randomized, open‐label, parallel‐group studies examined the effects of extended‐release (ER) oxymorphone on CYP2C9 or CYP3A4 metabolic activities in healthy subjects. On days −1, 7, and 14, subjects received either a CYP2C9 probe (tolbutamide 500 mg) or CYP3A4 probes (midazolam and [14C N‐methyl]‐erythromycin for the erythromycin breath test). Subjects were randomized to 5 groups: high‐dose oxymorphone ER (3 × 20 mg q12h) + naltrexone (50 mg q24h); low‐dose oxymorphone ER (10–20 mg q12h); rifampin (2 × 300 mg q24h), an inducer of CYP2C9 and CYP3A4 activities; naltrexone (50 mg q24h); or CYP probes alone (controls). Probe metabolism was significantly altered by rifampin on days 7 and 14 (P < .05), whereas probe metabolism was not significantly affected by low‐dose oxymorphone ER or by high‐dose oxymorphone ER plus naltrexone. Oxymorphone ER exhibits a minimal potential for causing metabolic drug‐drug interactions mediated by CYP2C9 or CYP3A4.

Assessment of beta blockade with propranolol

Each of seven subjects received on a weekly basis placebo or 10, 20, 40, 80, or 160 mg propranolol orally four times daily. The effect of propranolol on the resting heart rate and the heart rate response to the Valsalva maneuver, tilt, isoproterenol, and maximal exercise were measured. Coefficients of determination were calculated from the individual dose‐response curves. The results indicate that the resting heart rate and the tachycardiac response to the Valsalva maneuver and tilt cannot be used to estimate beta blockade. Propranolol concentrations correlated well (mean r2 = 0.80) with the isoproterenol dose ratio minus one, but isoproterenol challenges appear clinically inapplicable. Reduction in maximal exercise tachycardia correlated best with propranolol concentrations (mean r2 = 0.89) but, to the extent that exercise could not be performed, there was no reliable way of clinically documenting beta blockade and only the serum concentration of propranolol was available as an indicator of appropriate therapy.

Single‐Dose Pharmacokinetics, Safety, and Tolerance of Linopirdine (DuP 996) in Healthy Young Adults and Elderly Volunteers

The pharmacokinetics, safety, and tolerance of linopirdine ([3,3‐bis(4‐pyridinylmethyl)‐1‐phenylindolin‐2‐one];DuP 996) a potential therapeutic agent for Alzheimers disease, were assessed in double‐blind, placebo‐controlled, randomized studies in which single oral doses were given to 64 healthy young or elderly males. Young subjects received escalating doses of 0.5 to 55 mg, whereas elderly subjects were given doses of 20 to 45 mg. Linopirdine plasma and urine samples were quantified after liquid extraction by a specific HPLC method using UV detection. In both groups, linopirdine disposition was characterized by rapid absorption (mean Tmax, <1 hr) and elimination (mean t1/2, 0.4–3.2 hr). Urinary excretion of unchanged drug was negligible. The pharmacokinetic parameters showed large inter‐ and intrasubject variability. Linopirdine was well‐tolerated in both young and elderly volunteers. The most frequently reported adverse event was headache. The subjects who received linopirdine did not experience clinically important changes in vital signs, electrocardiograms (ECGs), electroencephalograms (EEGs), or clinical laboratory evaluations.

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.

Anticoagulant Pharmacodynamics of Tinzaparin Following 175 IU/kg Subcutaneous Administration to Healthy Volunteers

Tinzaparin, a sodium salt of a low-molecular-weight heparin (LMWH) produced via heparinase digestion, is used for the treatment of deep vein thrombosis (DVT) and pulmonary embolism in conjunction with warfarin for the prevention of DVT in patients undergoing hip or knee replacement surgery, and as an anticoagulant in hemodialysis circuits. Its average molecular weight ranges between 5500 and 7500 daltons (Da); the percentage of chains with molecular weight lower than 2000 Da is not more than 10% in the marketed tinzaparin formulation. While this fraction is generally considered pharmacologically inactive, this has never been evaluated in vivo. The importance of the < 2000 Da fraction on the anticoagulant pharmacodynamics of tinzaparin assessed by anti-Xa and anti-IIa activity was studied in a two-way crossover trial. In this trial, 30 healthy volunteers received a single 175 IU/kg subcutaneous administration of tinzaparin containing approximately 3.5% of the < 2000 Da fraction and a tinzaparin-like LMWH containing 18.3% of the < 2000 Da fraction. The anti-Xa/anti-IIa ratios of the drug substances were comparable at 1.5 and 1.7 for tinzaparin and the tinzaparin-like LMWH, respectively. Both formulations were safe and well tolerated. Mean maximum plasma anti-Xa activity (A(max)) was approximately 0.818 IU/ml at 4 h following tinzaparin injection. Mean maximum plasma anti-IIa activity was 0.308 IU/ml at 5 h postdose. Intersubject variation was lower (< 18% for both anti-Xa and anti-IIa metrics) than in previous fixed-dose administration studies. There was no correlation between anti-Xa or anti-IIa AUC or A(max) and bodyweight in the present study supporting the weight-adjusted dosing regimen. Individual anti-Xa and anti-IIa profiles following the single 175 IU/kg subcutaneous administration of the tinzaparin-like LMWH were similar to that obtained with tinzaparin. Based on average equivalence criteria, the two LMWH preparations were determined to be bioequivalent using either anti-Xa or anti-IIa activity as biomarkers. The calculated intrasubject variabilities were low (< 14% for anti-Xa activity and < 18% for anti-IIa activity) yielding little evidence for a significant Subject x Formulation interaction. In summary, anti-Xa and anti-IIa activity following a single subcutaneous administration of tinzaparin 175 IU/kg to healthy volunteers yielded activity consistent with targeted therapeutic levels derived from previous trials in adult DVT patients. Weight-based dosing for the treatment of DVT appears rational based on the reduction in anti-Xa and anti-IIa variability consistent with the recommendation derived from earlier fixed-dose pharmacokinetic studies. Furthermore, differences in the percentage of molecules in the < 2000 Da molecular weight fraction of tinzaparin do not translate into differences in anti-Xa and anti-IIa activity in vivo.

Effect of moricizine on the pharmacokinetics and pharmacodynamics of warfarin in healthy volunteers.

Moricizine HCl, a new orally active antiarrhythmic agent, induces its own hepatic metabolism and consequently may interfere with the metabolism of warfarin, a drug used commonly by cardiac patients that also is subject to extensive hepatic metabolism. Both drugs are also highly protein bound in plasma. To assess the possibility of an interaction, single‐dose sodium warfarin (25 mg oral Coumadin, Du Pont Pharmaceuticals, Wilmington, DE) pharmacokinetics, pharmacodynamics, and plasma protein binding were examined in 12 healthy mate volunteers 14 days before and 14 days after starting chronic oral moricizine HCl administration (250 mg every 8 hours). The terminal elimination rate constant of warfarin was increased by about 10% when measured in the presence of chronic moricizine administration. However, oral plasma clearance, apparent volume of distribution, maximum peak plasma concentration, time to reach peak concentration, and protein binding were unaffected. More importantly, there was no evidence of a pharmacodynamic interaction based on the prothrombin time profile. It was concluded that no clinically significant interaction occurs under these conditions.

Determination of bisnafide, a novel bis-naphthalimide anticancer agent, in human plasma by high-performance liquid chromatography with UV detection

A simple, specific, and sensitive high-performance liquid chromatographic (HPLC) assay utilizing ultraviolet (UV) detection for the determination of bisnafide in human plasma was developed, validated, and applied to plasma samples from patients undergoing cancer therapy. Plasma samples, containing an internal standard, XE842, were first deproteinized with 2.0 ml acetonitrile, and subsequently, 1.0 ml and pH 9 boric acid-potassium chloride-sodium hydroxide buffer (0.1 M) was added. To this mixture, 9.0 ml of ethyl ether was added then vortex mixed. Following centrifugation, the ether layer was back-extracted into 250 microliters of 0.1 M phosphoric acid, then removed by vacuum aspiration. A portion of the remaining acid layer was directly injected onto the HPLC. Bisnafide was quantified using a Shiseido Capcell Pak C8 HPLC column and ultraviolet detection (274 nm). The lower limit of quantification was 10 ng ml-1 using 1.0 ml plasma. The intraday precision (RSD) ranged from 2.7 to 8.6% over a concentration range of 10-1000 ng ml-1. The interday precision (RSD) ranged from 5.6 to 11.5%. Overall mean accuracy was +/- 5.2%. The drug was stable in frozen heparinized human plasma stored at -20 degrees C for at least 1 year and stable throughout at least two freeze-thaw cycles. This method was successfully utilized for quantifying plasma concentrations needed to study the clinical pharmacokinetics of bisnafide in patients undergoing cancer therapy.

Pharmacokinetic Interactions of Moricizine and Diltiazem in Healthy Volunteers

Sixteen healthy male volunteers completed a nonrandomized, sequential, three‐phase study. The three phases were 1) moricizine at 250 mg every 8 hours for 7 days with 12 days washout; 2) diltiazem at 60 mg every 8 hours for 7 days; and 3) concomitant administration of moricizine at 250 mg and diltiazem at 60 mg every 8 hours for 7 days. The plasma concentration‐time profiles were obtained at the end of each phase for moricizine, diltiazem (with its metabolites desacetyl‐diltiazem and N‐desmethyl‐diltiazem), and both when administered together. Under steady‐state conditions, there was a two‐way (opposing) pharmacokinetic drug interaction when moricizine and diltiazem were coadministered in healthy volunteers. Both maximum plasma concentration (Cmax) and the area under the plasma concentration‐time curve from time 0 to the end of administration (AUCτ) of moricizine increased significantly by 88.9% and 121.1%, respectively. Oral clearance (Clo) decreased by 54%. The terminal half‐life (t1/2) of moricizine was not affected, however (2.1 ± 0.5 hours versus 2.4 ± 0.7 hours). It is believed that these changes were due to the inhibition of hepatic metabolism by diltiazem, which resulted in an increased systemic availability of moricizine. Moricizine had opposite effects on the pharmacokinetics of diltiazem. Moricizine decreased the Cmax of diltiazem significantly (by 36%) and increased Clo by 52%. A small but statistically significant decrease in the t1/2 from 4.6 ± 1.3 hours to 3.6 ± 0.7 hours was observed. Despite this result, no remarkable changes (e.g., in Cmax, AUC, or t1/2) were found for the two major diltiazem metabolites desacetyl‐diltiazem and N‐desmethyl‐diltiazem. It appears that the pharmacokinetic interaction of moricizine and diltiazem was metabolic. With the increase in moricizine concentrations and the decrease in diltiazem concentrations, adjustments in dose may be required to achieve optimal therapeutic response when coadministering both agents.