Single-dose pharmacokinetics of terodiline, including a stable isotope technique for improvement of statistical evaluations

Genomic architecture of pharmacological efficacy and adverse events

The pharmacokinetic and pharmacodynamic disciplines address pharmacological traits, including efficacy and adverse events. Pharmacogenomics studies have identified pervasive genetic effects on treatment outcomes, resulting in the development of genetic biomarkers for optimization of drug therapy. Pharmacogenomics-based tests are already being applied in clinical decision making. However, despite substantial progress in identifying the genetic etiology of pharmacological response, current biomarker panels still largely rely on single gene tests with a large portion of the genetic effects remaining to be discovered. Future research must account for the combined effects of multiple genetic variants, incorporate pathway-based approaches, explore gene-gene interactions and nonprotein coding functional genetic variants, extend studies across ancestral populations, and prioritize laboratory characterization of molecular mechanisms. Because genetic factors can play a key role in drug response, accurate biomarker tests capturing the main genetic factors determining treatment outcomes have substantial potential for improving individual clinical care.

Applications of stable isotopes in clinical pharmacology

This review aims to present an overview of the application of stable isotope technology in clinical pharmacology. Three main categories of stable isotope technology can be distinguished in clinical pharmacology. Firstly, it is applied in the assessment of drug pharmacology to determine the pharmacokinetic profile or mode of action of a drug substance. Secondly, stable isotopes may be used for the assessment of drug products or drug delivery systems by determination of parameters such as the bioavailability or the release profile. Thirdly, patients may be assessed in relation to patient-specific drug treatment; this concept is often called personalized medicine. In this article, the application of stable isotope technology in the aforementioned three areas is reviewed, with emphasis on developments over the past 25 years. The applications are illustrated with examples from clinical studies in humans.

Analysis of Pharmacological Effects of Drugs Used for Treatment of Urinary Disturbance Based on Anticholinergic and Smooth Muscle-Relaxing Effects

Propiverine hydrochloride, oxybutynin hydrochloride and terodiline hydrochloride have both anticholinergic and antispasmodic effects, and are used for the management of urinary frequency and incontinence. The average standard therapeutic doses of these drugs differ greatly. We retrospectively analyzed their pharmacological effects with consideration given to muscarinic acetylcholine receptor binding affinities, anticholinergic activities, and inhibitory effects on KCl-induced contraction. Muscarinic acetylcholine receptor occupancies and the inhibitory ratios of the drugs for both acetylcholine-induced and KCl-induced contraction in a steady state after oral administration of standard doses were calculated based on pharmacokinetics and the receptor occupancy theory. The average muscarinic acetylcholine receptor occupancy and inhibitory ratio of acetylcholine-induced contraction were estimated to be 12.6+/-1.06% and 3.27+/-0.74%, respectively, with no significant differences found between the drugs for those parameters. A significant linear relationship was found between muscarinic acetylcholine receptor occupancy and the maximum ratio of increase in bladder urinary capacity. On the other hand, the inhibitory ratios of KCl-induced contraction varied from 0.01 to 0.48%. The present results suggest that muscarinic acetylcholine receptor occupancy is a principal determinant of the therapeutic effect of a drug used for treatment of urinary disturbance.

Estimating the contribution of genes and environment to variation in renal drug clearance

Renal excretion is the major pathway for elimination of many clinically used drugs and xenobiotics. We estimated the genetic component (rGC) contributing to variation in renal clearance for six compounds (amoxicillin, ampicillin, metformin, terodiline, digoxin and iohexol) using Repeated Drug Application methodology. Data were obtained from published literature. The rGC values of renal clearance of metformin, amoxicillin, and ampicillin, which undergo transporter-mediated secretion, ranged from 0.64-0.94. This finding suggests that variation in the renal clearance of these drugs has a strong genetic component. Additionally, the rGC values of renal clearance of metformin, amoxicillin, and ampicillin were similar to previously reported rGC values for metabolism. By contrast, the rGC values of renal clearance for iohexol, digoxin, and terodiline were low (0.12-0.37). Renal clearance of these compounds occurs mainly through passive processes (e.g. glomerular filtration and passive secretion/reabsorption). The low rGC values of iohexol, digoxin and terodiline suggest that environmental factors may contribute to variation in their renal clearance.

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.

Concomitant single-dose and multiple-dose pharmacokinetics of terodiline in man, with a note on its enantiomers and major metabolites

Single-dose and multiple-dose pharmacokinetics of terodiline were studied in 20 healthy volunteers by giving an initial oral dose of deuterium-labelled terodiline (12.5 mg or 25 mg) followed by multiple doses of Mictrol tablets (12.5 mg b.i.d. for 14 days and 25 mg b.i.d. for 14 days or vice versa). The enantiomer serum concentration ratio of S(-)/R(+) terodiline was close to unity at steady-state as well as during the disposition phase. The average single-dose kinetic parameters for the racemate after the 12.5 mg dose were: maximum serum concentration 41 micrograms/l, the corresponding time 3.4 hr, terminal half-life 61 hr, oral clearance 77 ml/min., renal clearance 12 ml/min. and apparent volume of distribution 382 1. The single-dose kinetics for the 25 mg dose and the multiple-dose kinetic parameters showed that linear kinetics prevailed. The average steady-state serum concentration was 275 micrograms/l at the lower dose and 509 micrograms/l at the higher dose. The degree of fluctuation during a dosage interval was 19% and the time to steady-state was about 9 days. The fraction unbound was about 8%. Unconjugated p-hydroxylated terodiline, p-hydroxy-m-methoxyterodiline and hydroxy-tert-butyl-terodiline constituted 15%, < 1% and 5%, respectively, of the terodiline steady-state levels.

Bioavailability and disposition of terodiline in man

Terodiline was concomitantly administered intravenously (12.5 mg) and orally ([2H]terodiline, 12.5 mg) to 10 healthy volunteers. In four of the subjects, a tracer dose of the intravenously given terodiline was 3H-labeled. In a separate study, six subjects were given [3H]terodiline orally. Estimated pharmacokinetic parameters were as follows: systemic clearance, 93 mL/min; renal clearance, 14 mL/min; volume of distribution at steady-state, 407 L; terminal half-life, 54 h; and mean residence time, 77 h. After intravenous infusion, a rapid distribution phase (half-life, 4.5 min) could be observed. The maximum serum concentration after the oral dose was 29 micrograms/L and the time to maximum concentration was 5 h (estimated by noncompartmental analysis). Absorption commenced within the first hour and by deconvolution the maximum rate of absorption was determined to occur between 1 and 3 h, and by 3.4 h 90% of the available dose had been absorbed. Calculation of bioavailability by noncompartmental AUC, two-compartmental analysis, urinary excretion, and 24-h oral/intravenous concentration ratio gave similar results (ANOVA test, not significant). About 75% and 25% of administered radioactivity could be recovered in urine and feces, respectively. Intact terodiline in feces accounted for about 1% of the dose. p-Hydroxyterodiline was quantitated in feces and accounted for about 5% of the dose. Another metabolite, 3,4-dihydroxyterodiline, which has not previously been detected in urine or serum, was also identified.

Use of stable isotopes for evaluation of drug delivery systems: comparison of ibuprofen release in vivo and in vitro from two biphasic release formulations utilizing different rate-controlling polymers

Certain delivery systems are intended to release the active ingredient in different phases to obtain the desired therapeutic effect. For these formulations, such as a bilayer tablet, it is desirable to distinguish and measure the release of drug from the different phases simultaneously. Mass spectrometric methods were developed to measure three ibuprofen isotopomers in serum and two in dissolution fluid. The analytical methods were linear (r > or = 0.992) over the concentration range of interest and recovery was greater than 99.2% for all isotopomers. Coadministration of [2H0]ibuprofen, [2H4]ibuprofen, and [2H7]ibuprofen to male beagles demonstrated that the isotopomers were bioequivalent and verified the absence of any kinetic isotope effect due to deuterium incorporation (p = 0.286). These methods were then used to evaluate a bilayer tablet formulation composed of an immediate release layer of 100 mg [2H4]ibuprofen and a sustained release layer with a drug load of 300 mg [2H0]ibuprofen. Two different rate-controlling polymer matrices that provided similar in vitro dissolution profiles were compared in the sustained release phase, while the immediate release formulation remained the same. In male beagles, the HPMC matrix delivered a significantly greater amount of ibuprofen (p < 0.05). The AUC was threefold greater for HPMC (1067 +/- 437 nmole*h/ml) versus EUDRAGIT (320 +/- 51), and Cmax was nearly four times greater (145 +/- 62.1 nmole/ml for HPMC versus 37.9 +/- 14.4 for EUDRAGIT).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of R(+)-terodiline given intravenously and orally to healthy volunteers

(+)-Terodiline was given orally (25 mg) and intravenously (12.5 mg) to eight healthy volunteers. The pharmacokinetics of (+)-terodiline could be described by a one compartment model. The lag time of absorption was 0.6 +/- 0.5 hr (mean +/- S.D.), the absorption half-life 0.9 +/- 0.5 hr, the time to maximum serum concentration 5.6 +/- 2.2 hr and the corresponding maximum serum concentration 62 +/- 22 micrograms/l. The volume of distribution was found to be 372 +/- 84 1, the systemic clearance 86 +/- 29 ml/min., the mean residence time 81 +/- 38 hr and the observed terminal half-life of elimination 56 +/- 26 hr. The urinary excretion of the intravenous dose was 12 +/- 6% and the renal clearance 10 +/- 5 ml/min. The bioavailability of (+)-terodiline was 93 +/- 19%. The present results indicate that (+)-terodiline as well as the racemate can be characterized as low clearance long half-life drugs. One subject was a poor hydroxylator of debrisoquine and exhibited a 3-fold decrease in clearance and increase in half-life of (+)-terodiline relative to extensive metabolizers. Observed pharmacological effects were mild accomodation disturbances and dry mouth, i.e. the same effects as those that may be seen at a corresponding dose of terodiline given as a racemic mixture.

Population characteristics of biological systems influenced by multicomponent random and uniform variation

The total variability associated with the pharmacokinetic disposition of seven therapeutic agents was decomposed into its source components. After differentiating and isolating random components from fixed uniform components of variance, the proportional contribution of random intersubject and intrasubject variance was evaluated. Statistical analysis utilized a mixed-effects probabilistic model which incorporated both random effects and fixed day-to-day effects. In some cases, time-within-day diurnal effects were also incorporated. While significant intersubject effects were found for all seven drugs studied, three of them were characterized by predominant intrasubject variance. Since intrasubject variance represents a measure of the stability of drug disposition, characterization of its relative magnitude is fundamentally important in assessing the therapeutic consequences of a given treatment at any given time. Significant diurnal effects were found which were strikingly invariant.

In vivo evaluation of the semi-simultaneous method for bioavailability estimation using controlled intravenous infusion as an 'extravascular' route of administration

A recently proposed method for bioavailability estimation, called the semi-simultaneous method, was evaluated in vivo in rats using methysergide as a test substance. In this method the test and the reference dose are administered with a short time interval and a model including the bioavailability parameters is fitted to the concentration-time profile. In the present study, in order to control the true bioavailability, intravenous infusion was used to mimic extravascular administration and various input profiles were produced. Mono-, bi- and triexponential disposition functions with the true and also various erroneous input models were fitted to the individual data sets. The models were also fitted to truncated data sets to mimic a situation where a long duration of sampling is precluded. A combined fitting-deconvolution procedure was also applied. The simi-simultaneous method gave precise and accurate estimates of the bioavailability in most groups and a robustness in the estimate concerning the model fitted was noted. The true input model could be identified for all data sets using common goodness-of-fit criteria. In the groups where a 'flip-flop' situation was created (slower input than elimination) a poorer precision and accuracy and a higher sensitivity concerning the model fitted was observed. The model fitting and the fitting-deconvolution procedure generally gave very similar results.

Pharmacokinetics of terodiline and a major metabolite in dogs with a correlation to a pharmacodynamic effect

The pharmacokinetics and pharmacodynamics of the anticholinergic and calcium antagonistic drug terodiline, N-tert-butyl-1-methyl-3,3-diphenylpropylamine, have been studied in beagle dogs. The bioavailability was about 25% (0.15 and 0.5 mg/kg), the terminal half-life 3 hr, the systemic clearance 40 ml/min..kg, the volume of distribution (V beta) about 7 l/kg and the unbound fraction in serum 0.14. p-Hydroxyterodiline and p-hydroxy-m-methoxyterodiline were quantitated and constituted 15-40% and 25%, respectively, of the amount excreted in urine (about 60% of the dose) and were the main metabolites, as in man. The dog was used as an experimental model to study the chronotropic effect. An increased heart rate was observed after acute administration of high doses of terodiline as well as after p-hydroxyterodiline. A 20% increase in heart rate was observed at a mean serum concentration of 1086 and 1010 micrograms/l following intravenous injection of terodiline or p-hydroxyterodiline, respectively. The corresponding unbound concentrations were 150 and 474 micrograms/l. The potency ratios of terodiline/p-hydroxyterodiline was 0.9 +/- 0.2 (based on total concentrations) and 3.2 +/- 0.8 (based on unbound concentrations). The estimated potency of parent drug and main metabolite and the fact that p-hydroxyterodiline constitutes 10-20% of the terodiline steady-state level in man, indicate that the contribution of the metabolite to the chronotropic effect observed in clinical studies is minor.

Tolerability and steady-state pharmacokinetics of terodiline and its main metabolites in elderly patients with urinary incontinence

The elderly form an important target group for the treatment of urinary urge incontinence with drugs such as terodiline (Mictrol, Terolin). In order to evaluate its steady-state pharmacokinetics and tolerability in geriatric patients terodiline 12.5 mg b.d. was given to 28 hospitalized patients with urinary incontinence (mean age 85 years) for six weeks. The patients were monitored during the study and for 6 weeks afterwards, blood samples being taken at regular intervals. In addition to these multi-diseased and polymedicated patients, a small, homogenous group of healthy volunteers (mean age 40 years) was studied as a reference group, being given terodiline 12.5 mg b.d. for 2 weeks. Terodiline was generally well tolerated by the patients and no significant change in blood pressure or heart rate were found. One patient was withdrawn due to adverse effects. The mean terminal half-life of terodiline was 131 h and the clearance after oral administration (clearance/systemic availability) was 39 ml.min-1. The corresponding figures for the healthy volunteers were 57 h and 75 ml.min-1. The average steady-state serum concentration was 518 micrograms.l-1 in the geriatric patients and 238 micrograms.l-1 in the healthy volunteers. Steady-state was reached within 3 weeks in 20 of the 28 patients and within 5 weeks in 7 patients. In the geriatric patients the steady-state serum concentration of the main metabolite p-hydroxyterodiline, during the last three weeks on terodiline was 45 micrograms.l-1, 57 micrograms.l-1, and 45 micrograms.l-1, respectively, and a similar value was found in the healthy volunteers, 47 micrograms.l-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Single- and multiple-dose pharmacokinetics of terodiline in geriatric patients

As a target group, geriataric patients were selected for pharmacokinetic studies with terodiline (Mictrol), an anticholinergic and calcium antagonist drug effective in the treatment of urinary incontinence. The single-dose kinetics in the geriatric patients (mean age 82 years) differed significantly from that previously found (Hallén et al. 1987) in healthy volunteers (mean age 35 years). There were higher peak serum concentrations (110 vs 79 micrograms.l-1), increased half-life (189 vs 60 h), lower renal clearance (4.0 vs 10.9 ml.min-1) and lower total clearance (29 vs 75 ml.min-1). Multiple-doses of 12.5 mg b.d. for 6-8 weeks resulted in a mean steady-state concentration of 642 micrograms.l-1, which was in agreement with the single dose parameters. The studied geriatric patients can be characterized not only as old, but also as frail, bedridden, having several diseases and polymedicated. The differences in pharmacokinetics between younger and elderly subjects can be attributed to a variety of complex factors, which may alter the clearance and/or the volume of distribution.