Pharmacotherapy for excessive daytime sleepiness

Excessive daytime sleepiness (EDS) has recognized detrimental consequences such as road traffic accidents, impaired psychological functioning and reduced work performance. EDS can result from multiple causes such as sleep deprivation, sleep fragmentation, neurological, psychiatric and circadian rhythm disorders. Treating the underlying cause of EDS remains the mainstay of therapy but in those who continue to be excessively sleepy, further treatment may be warranted. Traditionally, the amphetamine derivatives, methylphenidate and pemoline (collectively sympathomimetic) psychostimulants were the commonest form of therapy for EDS, particularly in conditions such as narcolepsy. More recently, the advent of modafinil has broadened the range of therapeutic options. Modafinil has a safer side-effect profile and as a result, interest in this drug for the management of EDS in other disorders, as well as narcolepsy, has increased considerably. There is a growing school of thought that modafinil may have a role to play in other indications such as obstructive sleep apnea/hypopnea syndrome already treated by nasal continuous positive airway pressure but persisting EDS, shift work sleep disorders, neurological causes of sleepiness, and healthy adults performing sustained operations, particularly those in the military. However, until adequately powered randomised-controlled trials confirm long-term efficacy and safety, the recommendation of wakefulness promoters in healthy adults cannot be justified.

Effect of duloxetine on tolterodine pharmacokinetics in healthy volunteers

AIM

To investigate the effect of duloxetine on the pharmacokinetics and tolerability of tolterodine and its active 5-hydroxymethyl metabolite (5-HM).

METHODS

Sixteen healthy subjects received two 5-day treatment regimens in a randomized, double-blinded, crossover fashion: tolterodine (2 mg, BID) + duloxetine (40 mg, BID), tolterodine (2 mg, BID) + duloxetine placebo (BID). Plasma concentrations of tolterodine and 5-HM were measured on day 5. Adverse events, clinical safety laboratory data and vital signs were assessed during the study.

RESULTS

Duloxetine increased the AUC(tau,ss) of tolterodine by 71%[geometric mean, 95% confidence interval (CI) 31, 123], and its C(max,ss) by 64% (CI 30, 106), and prolonged its t(1/2) by 14% (CI 1, 28). Duloxetine did not affect the plasma concentrations or t(1/2) of 5-HM. Laboratory data and vital signs did not reveal any clinically significant changes or abnormalities.

CONCLUSIONS

Duloxetine exhibited minor inhibitory effects on the pharmacokinetics of tolterodine but not 5-HM. Coadministration of these drugs was well tolerated and demonstrated no significant safety findings in the studied population. These findings suggest that there should not be a need for routine adjustment of tolterodine dosage in the presence of duloxetine.

Transdermal oxybutynin: for overactive bladder

Oxybutynin binds to the M(3) muscarinic receptors on the detrusor muscle of the bladder, preventing acetylcholinergic activation and relaxing the muscle. The transdermal system delivers oxybutynin over a 3- to 4-day period after application to intact skin. Peak plasma concentrations of oxybutynin and the major active metabolite, N-desethyloxybutynin, are reached 24 - 48 hours after a single application and therapeutic concentrations are maintained throughout the dosage interval. In a large, randomised, double-blind trial, transdermal oxybutynin 3.9 mg/day significantly decreased the median number of incontinence episodes per week compared with placebo (-19 vs -15, p = 0.0165) in patients with overactive bladder. In addition, the micturition frequency was reduced and average voided volume was increased by transdermal oxybutynin treatment. Significant reductions in incontinence episodes following transdermal oxybutynin treatment were also observed in two further studies and the clinical efficacy was similar to that of oral tolterodine or oral oxybutynin. Transdermal oxybutynin was well tolerated in clinical trials. Application site reactions were the most common adverse effect; however, the majority were mild to moderate in severity. Adverse events associated with anticholinergic drugs (e.g. dry mouth) were less frequently reported in patients treated with transdermal oxybutynin than in those receiving orally administered oxybutynin or tolterodine.

Effect of Antacid on the Pharmacokinetics of Extended-Release Formulations of Tolterodine and Oxybutynin

BACKGROUND

In general, extended-release (ER) formulations are designed to prolong the duration of efficacy and reduce the adverse effects of a drug. These formulations often contain the entire daily dose in a single tablet. Therefore, failure of the ER mechanism not only diminishes the desired benefits, but may temporarily expose the patient to drug concentrations higher than those released from a conventional tablet. In this study we determined whether pH has an effect on drug release from the ER formulations of oxybutynin (OROS technology) and tolterodine (membrane coated beads) in vitro and in vivo.

STUDY DESIGN

In vitro studies were based on standardised dissolution experiments for each drug in media of different pH (artificial gastric fluid at pH 1.2, artificial intestinal fluid at pH 7.5, and water). In the two separate, identically designed in vivo studies, single doses of each drug were administered alone and with an antacid to male and female healthy volunteers aged 18-45 years. The randomised, crossover, open-label in vivo studies employed a validated assay to determine plasma concentrations of tolterodine and its metabolite 5-hydroxymethyl tolterodine (5-HM), or oxybutynin and its metabolite N-desethyloxybutynin.

RESULTS

The in vitro study showed similar slow and steady drug release from ER-oxybutynin in each pH medium, with 64-71% released after 12 hours. Drug release from ER-tolterodine was steady and slow in artificial gastric fluid, with 72.5% of drug released after 12 hours. However, drug release was much faster in artificial intestinal fluid and water, where 69.8% and 69.1%, respectively, of the drug was released within 4 hours. These in vitro results were consistent with the findings of the in vivo studies. In vivo, the pharmacokinetic profile (peak plasma concentration [C(max)] and area under the concentration-time curve) of ER-oxybutynin was similar after administration with or without antacid, whereas C(max) values of both tolterodine and 5-HM increased significantly when ER-tolterodine was administered with antacid (p < or = 0.017 vs ER-tolterodine alone).

CONCLUSIONS

Changes in pH affected the release of tolterodine from ER-tolterodine, while they had no effect on the release of oxybutynin from the proprietary ER technology used in ER-oxybutynin. The technology employed in ER formulations thus determines sensitivity of drug release to external factors.

Update on overactive bladder: Pharmacologic approaches on the horizon

Limitations exist with regard to the array of available agents for the pharmacologic therapy of overactive bladder, including issues of efficacy and tolerability. It is clear that the ideal agent for this condition has not been identified. However, several new pharmacologic treatments, including some with novel approaches to drug delivery, have emerged in clinical development over the past few years. These agents include a variety of anticholinergics and others. In initial studies, some of the agents appear to compare favorably with existing therapies. Whether these promising results will hold up when subjected to large-scale, well-controlled clinical trials is unclear.

Clinical pharmacokinetic profile of modafinil

Modafinil is a unique wake-promoting agent for oral administration. Its pharmacological properties are distinct from those of other CNS agents, and it selectively targets neuronal pathways in the sleep/wake centres of the brain. After single or multiple oral doses, modafinil is readily absorbed, reaching maximum plasma concentrations at 2-4 hours after administration and pharmacokinetic steady state within 2-4 days. Its pharmacokinetics are dose-independent between 200 and 600 mg/day. The elimination half-life is approximately 12-15 hours, which is largely reflective of the pharmacokinetics of the longer-lived l-enantiomer. Modafinil is primarily eliminated via metabolism, mainly in the liver, with subsequent excretion in the urine. Less than 10% of the dose is excreted as unchanged drug. Metabolism is largely via amide hydrolysis, with lesser contributions from cytochrome P450 (CYP)-mediated oxidative pathways. In patients who are renally or hepatically compromised, the elimination processes can be slowed, and in a similar manner (although to a lesser extent), elimination in the elderly may be reduced due to normal effects of aging. Because modafinil is administered concomitantly with other medications, the potential for metabolic drug-drug interactions has been examined both in vitro and in vivo. In vitro, modafinil was observed to produce a reversible inhibition of CYP2C19 in human liver microsomes. It also caused a small, but concentration-dependent, induction of CYP1A2, CYP2B6 and CYP3A4 activities and suppression of CYP2C9 activity in primary cultures of human hepatocytes. Clinical studies have been conducted to examine the potential for interactions with methylphenidate, dexamfetamine, warfarin, ethinylestradiol and triazolam. The only substantive interactions observed were with ethinylestradiol and triazolam, apparently through induction of CYP3A4, primarily in the gastrointestinal system. Overall, the results of the interaction studies suggest that modafinil has potential to affect the pharmacokinetics of drugs that are metabolised by certain CYP enzymes. Compounds that induce or inhibit CYP activity are unlikely to have major effects on the pharmacokinetics of modafinil. In summary, the results show that modafinil is a moderately long-lived drug that is well absorbed and extensively metabolised.

Chiral analysis of d- and l-modafinil in human serum: application to human pharmacokinetic studies

Modafinil is a novel stimulant approved by the FDA for use in the management of excessive sleepiness associated with narcolepsy. Utility for other indications includes attention deficit-hyperactivity disorder (ADHD), depression, and management of cocaine dependence. To investigate the pharmacokinetics of modafinil in these patients, the authors improved and validated an HPLC method to separate and quantitate the separate enantiomers of modafinil in human serum. d- and l-Modafinil and the internal standard 3,3-diphenylpropylamine were extracted from serum, separated by gradient elution on a beta-cyclodextrin column, and then detected by UV absorbance at 225 nm. The elution gradient was developed to eliminate interferences by other drugs used to manage narcolepsy, ADHD, and stimulants of abuse, and endogenous substances in human serum. Validation studies included determination of stability, selectivity, precision, accuracy, and recovery. The method was used to investigate the pharmacokinetics of d- and l-modafinil in a volunteer after receiving 400 mg twice daily of racemic modafinil for 5 days. Interday and intraday assay variability (CV) typically ranged from 3% to 4%. The limits of detection (0.01 microg/mL) and quantitation (0.5 microg/mL) were well below the concentration expected in serum from patients receiving therapeutic doses of modafinil. The method was free from interference by methylphenidate, cocaine, commonly used antidepressants, and amphetamines. An example of apparent stereoselective disposition is presented as d-modafinil was eliminated more rapidly than l-modafinil from human serum. The validation data support the use of this method for human pharmacokinetic studies of modafinil in patients with known or suspected use of common antidepressants, psychostimulants, and drugs of abuse.

New perspectives on the overactive bladder: pharmacokinetics and bioavailability

In the United States alone, approximately 17 million men and women have symptoms of overactive bladder (OAB). For many years, oxybutynin was the drug of choice for treating OAB. Although it provided effective treatment, multiple daily doses were required, and adverse events, such as dry mouth and constipation, were decided drawbacks. Controlled drug delivery systems seen in commercially available OAB formulations alter the pharmacokinetics of antimuscarinic medications in ways that maintain efficacy and allow once-daily dosing and reduction of adverse events. In the future, OAB medications will not only incorporate new chemical entities, such as the S-enantiomer of oxybutynin, but will also use novel drug delivery technologies, including transdermal patches and bladder implants.

Genotoxic activation of benzophenone and its two metabolites by human cytochrome P450s in SOS/umu assay

The genotoxic potential of benzophenone and its metabolically related compounds, benzhydrol and p-benzoylphenol, was investigated using human cytochrome P450 (P450) enzymes. Benzophenone and its two metabolites (0.1-1mM) showed a suppression of bacterial growth without any P450 system, but no induction of umu gene expression was observed in Salmonella typhimurium TA1535/pSK1002. Human liver microsomes induced the bacterial cytotoxicity of these compounds without any umu gene expression. On the other hand, with the addition of Escherichia coli membranes expressing recombinant human P450 2A6 and NADPH-cytochrome P450 reductase (NPR), benzophenone showed umu gene expression (64 umu units/min/nmol) P450 2A6). Moderate activation of benzophenone by P450 1A1/NPR membranes, 1A2/NPR membranes, or 1B1/NPR membranes was also observed. Activation of benzhydrol and p-benzoylphenol by the P450/NPR system was similar to that of benzophenone. These results suggest that benzophenone and its metabolically related benzhydrol and p-benzoylphenol can be bioactivated by P450 2A6 and P450 family 1 enzymes. Until now, benzophenone has been investigated mainly in terms of estrogenic activity and cytotoxicity, however, the genotoxic activation of benzophenone by human cytochrome P450s should be examined in terms of the risks to humans.

Steady-state pharmacokinetics and tolerability of modafinil administered alone or in combination with dextroamphetamine in healthy volunteers

The potential for a drug-drug interaction between modafinil and dextroamphetamine, each at steady state, was investigated in an open-label, randomized, single-period studyin 32 healthy male and female volunteers. All subjects received modafinil orally once daily for 28 days (200 mg on Days 1-7; 400 mg on Days 8-28). On Days 22 to 28, half of the subjects also received dextroamphetamine (20 mg) orally 7 hours after modafinil. Samples for pharmacokinetic (PK) profiling were obtained on Days 21 and 28. The mean changes in PK parameters for modafinil and its two circulating metabolites between the two groups were not statistically significantly different, except Cmax for modafinil acid. Adverse events obtained in the two groups were similar and mild or moderate in nature. The results indicate that administration of low-dose dextroamphetamine in this dosing regimen does not alter the steady-state pharmacokinetics of modafinil. The combination has a similar tolerability profile as modafinil alone.

A multicenter, prospective, open-label study of tolterodine extended-release 4 mg for overactive bladder: the speed of onset of therapeutic assessment trial (STAT)

BACKGROUND

Antimuscarinic agents are the primary treatment for overactive bladder (OAB), but there is a lack of information regarding when maximum symptom relief and maximum perceived patient benefit occur.

OBJECTIVE

This study assessed the speed of onset of therapeutic benefit with tolterodine extended-release (ER) 4 mg.

METHODS

This 12-week, multicenter, prospective, open-label study enrolled patients with OAB who either had received no previous pharmacologic treatment for OAB (drug naive) or were receiving such treatment at enrollment (previously treated). Efficacy was assessed at 1, 4, and 12 weeks using a micturition diary and measures of patients' and physicians' perceptions of improvement. Safety was assessed in terms of adverse events and study withdrawals.

RESULTS

The intent-to-treat population included 1138 patients (302 men, 836 women; 88.4% white; age range, 18-91 years), 735 drug naive and 403 receiving treatment for OAB at enrollment. After 1 week, tolterodine ER 4 mg had produced a significant improvement in all efficacy variables in both groups of patients (P < 0.01); 72% of the maximum effect on urge incontinence was observed in both groups; and 84.7% of drug-naive patients and 83.6% of previously treated patients perceived a benefit from treatment. After 4 weeks, drug-naive and previously treated patients reported a respective 93% and 100% of the maximum effect on episodes of urge incontinence. Tolterodine was well tolerated, with dry mouth (mostly mild) the most commonly reported adverse event (15.5% in each group). The 330 (81.9%) patients who had reported unacceptable efficacy and the 87 (21.6%) patients who had reported unacceptable tolerability of previous OAB treatment responded favorably to tolterodine ER 4 mg.

CONCLUSIONS

Tolterodine ER 4 mg was effective and well tolerated in both drug-naive and previously treated patients with OAB. More than 80% of patients reported benefit from treatment after 1 week, but maximum symptom relief was achieved with longer treatment.

Effect of modafinil at steady state on the single-dose pharmacokinetic profile of warfarin in healthy volunteers

Modafinil has been reported to produce a concentration-related suppression of CYP2C9 activity in vitro in primary cultures of human hepatocytes. To determine whether this effect occurs in vivo, the pharmacokinetics of (S)-warfarin was investigated after single oral doses of racemic warfarin (5 mg; COUMADIN) in a placebo-controlled, single-blind, single-period study in 28 volunteers. Subjects received an oral dose of warfarin prior to administration of modafinil (200 mg for 7 days, followed by 400 mg for 21 days) or placebo and they received another after 4 weeks of treatment. Treatment with modafinil did not significantly alter the pharmacokinetics of (S)- or (R)-warfarin relative to placebo. Since (S)-warfarin is predominantly metabolized via CYP2C9, the results indicate that the marked suppression of CYP2C9 activity in vitro does not translate into a similar effect clinically. However, limitations arising from investigation of single doses of warfarin preclude global conclusions about the potential for more subtle interactions after chronic warfarin administration.

The effect of tolterodine on the pharmacokinetics and pharmacodynamics of a combination oral contraceptive containing ethinyl estradiol and levonorgestrel

BACKGROUND

Tolterodine is an antimuscarinic agent for the treatment of overactive bladder, a chronic condition that is particularly common in women. Given the prevalence pattern of overactive bladder and the widespread use of oral contraception, circumstances are likely to arise in which physicians may wish to prescribe tolterodine for patients already taking oral contraceptives. Based on a search of MEDLINE from 1990 to 2001, there have been no studies of whether concomitant use of these agents entails a risk of drug-drug interaction or conception.

OBJECTIVE

This study investigated the effects of tolterodine on the pharmacokinetics and pharmacodynamics of a low-dose combination oral contraceptive (ethinyl estradiol 30 microg/levonorgestrel 150 microg).

METHODS

This was an open-label, randomized, 2-period crossover study in healthy women. Oral contraception was given for 21 days either alone or in combination with oral tolterodine 2 mg BID (on days 1-14) over two 28-day contraceptive cycles. Pharmacokinetic assessments were performed on day 14 based on plasma levels of ethinyl estradiol and levonorgestrel up to 24 hours after dosing and serum tolterodine levels at 1 to 3 hours after dosing. The potential for pharmacodynamic interaction was assessed in terms of the risk of failure of suppression of ovulation based on serum levels of estradiol and progesterone measured throughout each cycle.

RESULTS

Twenty-four healthy women (age, 23-41 years [mean, 30 years]; height, 155-178 cm [mean, 167 cm]; body weight, 51-75 kg [mean, 64 kg]) participated in the study. There was no evidence of a pharmacokinetic interaction between tolterodine and the steroid hormones in the oral contraceptive used, nor did the oral contraceptive show any relevant pharmacokinetic interaction with tolterodine. Serum levels of estradiol and progesterone indicated suppression of ovulation in both treatment periods.

CONCLUSION

In this selected population. coadministration of tolterodine did not affect the contraceptive efficacy of a low-dose combination oral contraceptive containing ethinyl estradiol and levonorgestrel.

Food does not influence the pharmacokinetics of a new extended release formulation of tolterodine for once daily treatment of patients with overactive bladder

OBJECTIVE

To determine whether food intake influences the pharmacokinetics of a new, once daily, extended release (ER) capsule formulation of tolterodine in healthy volunteers, and to compare its bioavailability with that of the existing immediate release (IR) tablet.

DESIGN

Open, randomised, 3-way crossover trial.

PARTICIPANTS

17 healthy volunteers (3 females, 14 males) aged between 19 and 50 years. With the exception of 1 male volunteer, all participants were classified as extensive metabolisers by cytochrome P450 2D6 genotyping.

METHODS

Volunteers received single oral doses of tolterodine L-tartrate ER 8 mg (2 x 4 mg capsules) on an empty stomach or with a standardised high-fat breakfast. Reference therapy comprised tolterodine L-tartrate IR 4 mg (2 x 2 mg tablets), administered in the fasting state. Serum concentrations of tolterodine, its active 5-hydroxymethyl metabolite (5-HM) and the active moiety (sum of unbound tolterodine + 5-HM) were measured for up to 72 hours post-dose. Safety endpoints were also determined.

RESULTS

No effect of food on the bioavailability of tolterodine ER capsules was apparent and there was no sign of dose-dumping with meals. The geometric mean fed:fasting ratio of area under the serum concentration-time curve to infinity (AUCinfinity) of the active moiety, for all volunteers combined, was 0.95 (90% confidence interval 0.88 to 1.03). Equivalence with respect to AUCinfinity (dose-corrected) was also found for the ER capsule compared with the IR tablet, although uncorrected maximum serum concentrations were around 50% lower despite the fact that the capsule dose was twice as high. Seven volunteers reported adverse events, predominantly headache. No volunteer reported dry mouth. Overall, there were no safety concerns.

CONCLUSIONS

The new ER formulation of tolterodine shows no pharmacokinetic interaction with food. On the basis of these results, patients with overactive bladder may, therefore, be advised to take the drug without regard to the timing of meals, maximising convenience during therapy.

Evidence for the efficacy and safety of tolterodine in the treatment of overactive bladder

Overactive bladder (OAB) is a chronic and prevalent condition, the symptoms of which (urinary frequency and urgency, with or without urge incontinence) can exert a profound negative effect on a person's daily life activities. Tolterodine (Detrol in North America and Detrusitol in the rest of the world, Pharmacia), a competitive muscarinic antagonist, is the first agent of this class to be specifically developed for the treatment of OAB. This agent displays in vivo functional selectivity for the bladder over other tissues that contain muscarinic receptors (e.g., salivary glands, eye), which translates into good efficacy and tolerability in patients with OAB (including the elderly). Comparative, randomised, double-blind studies show that tolterodine (administered as immediate-release [IR] tablets 2 mg b.i.d.) is as effective as oxybutynin (5 mg t.i.d.) in improving all of the troublesome symptoms of OAB but with a significantly lower incidence and severity of dry mouth. The advent of a new extended-release (ER) capsule formulation of tolterodine (4 mg) for convenient once-daily treatment builds upon these findings, with significantly improved efficacy for reducing urge incontinence episodes and a lower frequency of dry mouth relative to the existing IR tablet (2 mg b.i.d.). Tolterodine can therefore be considered a valuable, well-tolerated treatment option for patients with OAB, providing improvements in symptoms that are both clinically meaningful to patients and sustained during long-term treatment.

Multiple dose pharmacokinetics of a new once daily extended release tolterodine formulation versus immediate release tolterodine

OBJECTIVE

To determine the multiple dose pharmacokinetics of a new extended release (ER) capsule formulation of tolterodine, compared with the existing immediate release (IR) tablet, in healthy volunteers.

DESIGN

Nonblind, randomised, 2-way crossover trial.

PARTICIPANTS

19 healthy volunteers (7 females, 12 males), mean age 33 years (range 18 to 55 years). Prior to the study, all volunteers were classified as either extensive or poor metabolisers by cytochrome P450 2D6 genotyping.

METHODS

Volunteers received tolterodine ER 4mg once daily or tolterodine IR 2mg twice daily for 6 days (all doses given as the L-tartrate salt). A washout period of 7 days separated the 2 treatments. Serum concentrations of tolterodine, its active 5-hydroxymethyl metabolite (5-HM) and the active moiety (extensive metabolisers: sum of unbound tolterodine + 5-HM; poor metabolisers: unbound tolterodine) were measured for up to 48 hours post-dose on day 6 (steady state). Tolerability was also determined.

RESULTS

17 volunteers (13 extensive metabolisers, 4 poor metabolisers) completed the study and were evaluable for both treatment periods. The 90% confidence interval for the geometric mean ratio of area under the serum concentration-time curve to 24 hours (AUC24) of the active moiety, for all volunteers combined, indicated equivalence for the 2 formulations. Pooled analysis also demonstrated that the peak serum concentration (Cmax) of the active moiety following administration of tolterodine ER was around 75% of that observed for the IR tablet, whereas the trough concentration was around 1.5-fold higher. Overall, the pharmacokinetics of tolterodine (irrespective of genotype) and 5-HM (extensive metabolisers only) were consistent with sustained drug release over 24 hours. Tolterodine ER was well tolerated.

CONCLUSIONS

The new once daily ER formulation of tolterodine 4mg shows pharmacokinetic equivalence (AUC24) to the existing IR tablet given at a dose of 2mg twice daily. Findings of lower Cmax for tolterodine ER may explain the significantly lower rate of dry mouth subsequently observed in patients with overactive bladder.

Physiologically based pharmacokinetic model for tetrachlorobenzyltoluenes in rat: comparison of in vitro and in vivo metabolic rates

Ugilec 141 is a technical mixture of tetrachlorobenzyltoluenes (TCBTs). It was introduced in the early 1980s as a replacement for polychlorinated biphenyls (PCBs). Based on physicochemical properties and accumulation in the environment, the use of this mixture was prohibited. To gain more insight in the toxicokinetics of these compounds in mammals, rats were exposed to a single iv bolus injection of a mixture of 3 TCBTs. At different time points after dosing, the tissue and blood concentrations of the TCBTs were determined. The adipose tissue is the main storage compartment, followed by skin and muscle. The TCBTs were rapidly eliminated from the liver and the blood, with half lives ranging from 65 to 72 h. Additionally, the tissue concentration data for all 3 TCBTs were analyzed using a physiologically based pharmacokinetic (PB-PK) model. Sensitivity analysis illustrated that the elimination of the TCBTs was not influenced by metabolism only, but also by the blood flow through the liver. Furthermore, the metabolic rates derived from the model were compared to previously reported in vitro metabolic rates. The in vitro values for the TCBTs were only a factor 2 to 3 smaller than the in vivo metabolic rates, indicating the value of in vitro techniques for a priori parameterization of PB-PK models.

Steady-state pharmacokinetics and tolerability of modafinil given alone or in combination with methylphenidate in healthy volunteers

The potential for a pharmacokinetic (PK) drug-drug interaction between modafinil and methylphenidate, each at steady state, was investigated in an open-label, randomized, single-period study in 32 healthy male and female volunteers. All subjects received modafinil once daily orally for 28 days (200 mg on Days 1-7 and 400 mg on Days 8-28). On Days 22 to 28, half of the subjects also received 20 mg of methylphenidate orally 8 hours after their modafinil dose. PK profiles of modafinil were obtained on Days 21 and 28 and compared between the two groups. There were no statistically significant differences between the treatment groups in the mean changes in PK parameters for modafinil. Parameters for its metabolites were also similar between the groups, and all treatments were well tolerated. The results indicate that administration of low-dose methylphenidate 8 hours after treatment with modafinil does not appear to alter the steady-state pharmacokinetics of modafinil in healthy volunteers.

Identification of a selective nonpeptide antagonist of the anaphylatoxin C3a receptor that demonstrates antiinflammatory activity in animal models

The anaphylatoxin C3a is a potent chemotactic peptide and inflammatory mediator released during complement activation which binds to and activates a G-protein-coupled receptor. Molecular cloning of the C3aR has facilitated studies to identify nonpeptide antagonists of the C3aR. A chemical lead that selectively inhibited the C3aR in a high throughput screen was identified and chemically optimized. The resulting antagonist, N(2)-[(2,2-diphenylethoxy)acetyl]-L-arginine (SB 290157), functioned as a competitive antagonist of (125)I-C3a radioligand binding to rat basophilic leukemia (RBL)-2H3 cells expressing the human C3aR (RBL-C3aR), with an IC(50) of 200 nM. SB 290157 was a functional antagonist, blocking C3a-induced C3aR internalization in a concentration-dependent manner and C3a-induced Ca(2+) mobilization in RBL-C3aR cells and human neutrophils with IC(50)s of 27.7 and 28 nM, respectively. SB 290157 was selective for the C3aR in that it did not antagonize the C5aR or six other chemotactic G protein-coupled receptors. Functional antagonism was not solely limited to the human C3aR; SB 290157 also inhibited C3a-induced Ca(2+) mobilization of RBL-2H3 cells expressing the mouse and guinea pig C3aRS: It potently inhibited C3a-mediated ATP release from guinea pig platelets and inhibited C3a-induced potentiation of the contractile response to field stimulation of perfused rat caudal artery. Furthermore, in animal models, SB 290157, inhibited neutrophil recruitment in a guinea pig LPS-induced airway neutrophilia model and decreased paw edema in a rat adjuvant-induced arthritis model. This selective antagonist may be useful to define the physiological and pathophysiological roles of the C3aR.

The overactive bladder in children: a potential future indication for tolterodine

OBJECTIVE

To determine the safety, efficacy and pharmacokinetics of tolterodine in children with an overactive bladder.

PATIENTS AND METHODS

Thirty-three children (20 boys and 13 girls, aged 5-10 years) with an overactive bladder and symptoms of urgency, frequency and/or urge incontinence were enrolled in an open, dose-escalation study. Patients were treated with oral tolterodine 0.5 mg (n = 11), 1 mg (n = 10) or 2 mg (n = 12) twice daily for 14 days. The primary safety endpoint was the change in residual urinary volume, as determined by ultrasonography. In addition, voiding diary variables (frequency and incontinence episodes) and pharmacokinetics were evaluated. Other safety endpoints included laboratory variables, electrocardiogram recordings and reported adverse events.

RESULTS

There were no safety concerns in terms of the change in residual urinary volume for any of the three dosage groups; values were comparable with baseline after 2 weeks of treatment for all three dosages. Adverse events were reported by 20 patients (six on 0.5 mg, five on 1 mg, and nine on 2 mg). Most adverse events were not considered to be drug-related; of the 13 possibly related events, 10 occurred in those taking 2 mg. Headache was the most commonly reported adverse event. No serious adverse events were reported and there were no general safety concerns. There was an improvement in voiding diary variables in all treatment groups after 2 weeks of treatment, although the efficacy was greatest in those taking 1 mg and 2 mg. Pharmacokinetic findings were consistent with dose linearity over the range 0.5-2 mg.

CONCLUSION

The results support the use of 1 mg twice daily as the optimal dose of tolterodine for treating children aged 5-10 years with an overactive bladder.

Food increases the bioavailability of tolterodine but not effective exposure

The objective of this study was to investigate the influence of food on the pharmacokinetics of tolterodine, its active 5-hydroxymethyl metabolite (5-HM), and exposure to the active moiety (sum of unbound tolterodine + 5-HM) in healthy volunteers. Serum concentrations of tolterodine and 5-HM were measured for up to 12 hours after a single oral dose (2 mg) of tolterodine L-tartrate, administered either on an empty stomach or with a standardized medium-fat breakfast. All 23 subjects completing the study were classified as extensive metabolizers (phenotyped with debrisoquine). Pharmacokinetic data on tolterodine and the active moiety were evaluable for 22 subjects; all completing subjects were evaluable for 5-HM pharmacokinetics. Based on Cmax and AUC(infinity) ratios, relative bioavailability of tolterodine in the presence of food was 1.49 (90% confidence interval [CI], 1.35-1.71) and 1.53 (1.35-1.72), respectively. The pharmacokinetics of 5-HM and the active moiety were unaffected by food, as were the rates of drug absorption and terminal half-lives of tolterodine and 5-HM. Given that bioequivalence was observed for the active moiety underfed and fasting conditions, the authors concluded that coadministration of tolterodine with food is not expected to have any clinically relevant effects.

Tissue distribution of tolterodine, a muscarinic receptor antagonist, and transfer into fetus and milk in mice

Tolterodine ((R)-N,N-diisopropyl-3-(2-hydroxy-5-methyl-phenyl)-3-phenylpropanamine, CAS 124937-51-5) is an antimuscarinic agent developed specifically for the treatment of the overactive bladder. In this study, the extent and profile of tissue distribution of 14C-tolterodine, after single and repeat oral dosing, was investigated in the mouse. Overall, distribution of radioactivity in tissues was rapid, and there were no gender-specific differences. The concentration of radioactivity in most tissues was similar to, or exceeded, that in blood. Highest concentrations were measured in gall bladder, urinary bladder, liver, kidneys and lungs, while the lowest concentration (10-times lower than in plasma) was seen in the brain. The distribution pattern after repeat oral dosing was similar to that after a single dose, although the decline in tissue concentrations was slower. Studies in pregnant mice showed that the distribution of radioactivity differed between dams and fetuses. Radioactivity was low and showed homogeneous distribution in the fetus, while a heterogeneous pattern was seen in the dam. Highest concentrations were seen in the fetal liver, brain and spinal cord. Some accumulation was observed in the choroid plexus. Placental concentrations of radioactivity were generally higher than those in the fetus, with some accumulation in the yolk sac. Studies in suckling mouse pups showed low levels of exposure to drug-related radioactivity (around 0.2% of the dose); the milk:plasma concentration ratio was 0.0-0.7. In conclusion, tolterodine and its metabolites are rapidly distributed into tissues following oral administration of radiolabelled drug in the mouse, with many tissues (including the fetus) reaching similar concentrations to that observed in blood. In other tissues, especially the eliminating organs, radioactivity levels were much higher than in blood. Penetration of the central nervous system was low, suggesting that the risk of deleterious effects on cognitive function may be lower with tolterodine than with more lipophilic antimuscarinic drugs.

Pharmacokinetics of tolterodine, a muscarinic receptor antagonist, in mouse, rat and dog. Interspecies relationship comparing with human pharmacokinetics

Tolterodine ((R)-N,N-diisopropyl-3-(2-hydroxy-5-methyl-phenyl)-3-phenylpropanamine, CAS 124937-51-5) is an antimuscarinic agent developed specifically for the treatment of the overactive bladder. In this study, the pharmacokinetics of tolterodine were investigated in the mouse, rat and dog, following which allometric scaling was performed to predict oral pharmacokinetics in man. The intestinal absorption of tolterodine after oral dosing was almost complete in all three species, with peak serum concentrations observed within 1 hour post-dose. Bioavailability varied between 2-20% in rodents and 58-63% in the dog. A high volume of distribution in all three species was consistent with extravascular distribution. Tolterodine was extensively metabolised in all the animal models, but the profile of metabolism differed in the rat compared to the mouse and dog, the latter having similar metabolism routes as man. Limitation of metabolism capacity caused a non-linear increase of tolterodine concentrations with dose (repeat-dose study in the mouse), and changed the relative metabolite concentration pattern. The results suggest that the hydroxylation of tolterodine is a high affinity, low capacity pathway, while N-dealkylation follows a low affinity, high capacity pathway. The elimination of tolterodine from serum was rapid, with a half-life of less than 2 h in all species. A very high clearance in the mouse and rat (10-15 l/h.kg), and in the dog (1.4 l/h.kg), indicated additional non-metabolic clearance mechanisms for tolterodine (shown to be attributed to biliary excretion). Urinary excretion of compound-related radioactive substance was around 15%, 45% and 50%, respectively, in the rat, mouse and dog. Allometric scaling allowed a good prediction of clearance and volume of distribution to be extrapolated for comparison with tolterodine pharmacokinetics in man. In conclusion, the pharmacokinetics of tolterodine are similar in the mouse and dog, and correlate with that in man. Although the rat has a different metabolic profile, clearance fits into the allometric relationship between species, enabling prediction of total clearance of tolterodine in man from preclinical data.

[Enantioselective pharmacokinetics of benproperine in healthy volunteers]

AIM

To investigate the enantioselective pharmacokinetic process of benproperine in healthy volunteers.

METHODS

An enantiospecific HPLC method was developed and used to determine the plasma concentrations of each enantiomer. Six healthy Chinese male volunteers received an oral dose of 60 mg (+/-)-benproperine. The ratios of the enantiomers in plasma samples were measured on a chiral AGP column. The plasma concentration of each enantiomer was then calculated using the ratios of enantiomers and total concentration of the two enantiomers previously measured.

RESULTS

The plasma levels of (-)-(S)-benproperine were always significantly higher than those of its antipode in six volunteers. The mean AUC0-t and Cmax values for (-)-(S)-benproperine were 2.18 and 2.12 times higher than those of (+)-(R)-benproperine. There was no significant difference between the T1/2 for both enantiomers, tested by paired t test (P > 0.05). Half an hour after administration of benproperine, the S/R ratio in plasma samples was as high as 3.8, and in 2 hours it drastically decreased to about 2.2, then kept on till 24 hours.

CONCLUSION

Benproperine showed significant enantioselective pharmacokinetics in the human after an oral dose of the racemate.

Pharmacokinetics and renal excretion of diphenhydramine and its metabolites, diphenylmethoxyacetic acid and diphenhydramine-N-oxide, in developing lambs

The developmental disposition of diphenhydramine (DPHM) and its metabolites, diphenylmethoxyacetic acid (DPMA) and DPHM-N-oxide (DPHMNO), was investigated in postnatal lambs. Lambs received a DPHM intravenous (iv) bolus 15 days (Group A; n = 5) or 2 months (Group B; n = 6) after birth. Total body clearance of DPHM in postnatal lambs (Group A = 138.7 +/- 80.5 mL/min/kg; Group B = 165.7 +/- 51.3 mL/min/kg) was similar to the nonplacental clearance values (i.e., the component of fetal total body clearance that is not due to elimination via the placenta) estimated for fetal lamb (116.3 +/- 49. 6 mL/min/kg), and significantly greater than estimates in adult sheep (38.5 +/- 12.3 mL/min/kg). In addition, Group A DPHM renal clearance (CL(r), >1.80 +/- 1.24 mL/min/kg) was similar to that of the fetus (2.06 +/- 0.24 mL/min/kg), and significantly greater than that for Group B (0.26 +/- 0.17 mL/min/kg) and the adult (0.012 +/- 0.005 mL/min/kg). In contrast, similar to the fetal situation, postnatal DPMA CL(r) (Group A = 0.02 +/- 0.02 mL/min/kg; Group B = 0.05 +/- 0.01 mL/min/kg) was significantly less than adult values (0. 53 +/- 0.19 mL/min/kg). Because DPMA is not sequentially metabolized in sheep, the lower CL(r) in postnatal lambs results in longer apparent elimination half-lives of this metabolite (Group A = 90.4 +/- 32.2 h; Group B = 13.13 +/- 11.0 h) compared with that in the adult (2.9 +/- 1.6 h). No age-related difference in DPHMNO CL(R) was observed. Alterations in the CL(r) of DPHM and DPMA are likely related to differences in the rate of development of mechanisms (i.e. , tubular secretion and reabsorption and glomerular filtration rate) involved in the urinary drug excretion of organic acids and bases.

Biotransformation rates of Ugilec 141 (tetrachlorobenzyltoluenes) in rat and trout microsomes

In vitro biotransformation rates of tetrachlorobenzyltoluene (TCBT) isomers 3,3',4,4'-Cl4-2-Me (TCBT 87), 3,3',4,4'-Cl4-5-Me (TCBT 88), and 3,3',4',5-Cl4-4-Me (TCBT 94) were determined using trout and rat hepatic microsomes. The disappearance of the TCBTs from the in vitro system followed first-order kinetics. The estimated biotransformation constants (k) for the rat ranged from 0.96 to 4.14 h(-1). Biotransformation rates for trout microsomes were much lower and ranged from 0.009 to 0.017 h(-1).

Fluoxetine inhibits the metabolism of tolterodine-pharmacokinetic implications and proposed clinical relevance

AIMS

To investigate the change in disposition of tolterodine during coadministration of the potent cytochrome P450 2D6 (CYP2D6) inhibitor fluoxetine.

METHODS

Thirteen patients received tolterodine l-tartrate 2 mg twice daily for 2.5 days, followed by fluoxetine 20 mg once daily for 3 weeks and then concomitant administration for an additional 2.5 days. They were characterized as extensive metabolizers (EM1 with one functional CYP2D6 gene, EM2 with two functional genes) or poor metabolizers (PM).

RESULTS

Nine patients, three EM2 and four EM1 and two PM, completed the trial. Following tolterodine administration, the area under the serum concentration-time curve (AUC) of tolterodine was 4.4-times and 30-times higher among EM1 and PM, respectively, compared with EM2. The AUC of the 5-hydroxymethyl metabolite (5-HM) was not quantifiable in PM. Fluoxetine significantly decreased (P<0.002) the oral clearance of tolterodine by 93% in EM2 and by 80% in EM1. The AUC of 5-HM increased in EM2 and decreased in EM1. However, the exposure to the active moiety (unbound tolterodine +5-HM) was not significantly increased in the two phenotypes. The subdivision of the EM group showed a 2.1-fold increase in active moiety in EM2 but the exposure was still similar to EM1 compared with before the interaction.

CONCLUSIONS

The study suggests a difference in the pharmacokinetics of tolterodine and its 5-hydroxymethyl metabolite depending on the number of functional CYP2D6 genes. Fluoxetine significantly inhibited the hydroxylation of tolterodine. Despite the effect on the pharmacokinetics of tolterodine in extensive metabolizers, the clinical effect is expected to be within normal variation.

Tolterodine use for symptoms of overactive bladder

OBJECTIVE

To describe the pharmacology, pharmacokinetics, clinical efficacy, and safety of tolterodine for the treatment of overactive bladder.

DATA SOURCES

Published articles and abstracts were identified from a MEDLINE search (January 1980-October 1998) using the terms tolterodine, PNU-200583E, urge incontinence, overactive bladder, detrusor instability, detrusor overactivity, and antimuscarinic. Pertinent articles written in English were considered for review. Additional articles were identified from the bibliographies of retrieved articles. Data from the Food and Drug Administration-approved product labeling and the manufacturer were also used in the absence of published data.

STUDY SELECTION AND DATA EXTRACTION

Clinical studies of tolterodine involving human subjects were evaluated.

DATA SYNTHESIS

Tolterodine is a competitive muscarinic receptor antagonist with relative functional selectivity for bladder muscarinic receptors. It is metabolized in the liver by CYP2D6 to an active metabolite (DD 01), which is partially responsible for its pharmacologic activity. Those who are genetically devoid of CYP2D6 will have higher concentrations of the parent compound and virtually undetectable concentrations of DD 01; however, the clinical efficacy does not appear to be altered. In dosages of 2 mg twice daily, tolterodine has shown consistent reductions in the number of micturitions per 24 hours and less consistently decreased incontinence episodes in patients with detrusor overactivity. The functional selectivity of tolterodine for bladder muscarinic receptors results in fewer systemic adverse effects, such as dry mouth, than occur with comparable nonselective antimuscarinic agents.

CONCLUSIONS

Clinical studies have shown that the effectiveness of tolterodine for symptoms of overactive bladder is similar to that of oxybutynin. The adverse effect profiles of tolterodine and oxybutynin are similar; however, comparative clinical trials have shown significantly fewer patients taking tolterodine require dosage reductions or discontinue therapy due to antimuscarinic adverse effects such as dry mouth. Although more costly than oxybutynin, tolterodine represents a modest improvement over oxybutynin with respect to adverse effect profile, which may allow more patients with incontinence to tolerate therapeutic doses. Further research is necessary to determine whether tolterodine has clinical advantages over similar agents in patients with other muscarinic adverse effects, such as constipation or cognitive impairment.

Tolterodine in the treatment of overactive bladder: analysis of the pooled phase II efficacy and safety data

OBJECTIVES

To summarize the efficacy and safety of tolterodine from the pooled data of four multicenter, randomized, double-blind, placebo-controlled, dose-ranging, parallel-group Phase II studies in patients with urodynamically proved overactive bladder (detrusor instability or detrusor hyperreflexia) and to analyze the concentration-effect relation.

METHODS

After a 1-week run-in period to establish baseline values, 319 patients were randomized to receive placebo or tolterodine 0.5, 1, 2, or 4 mg twice daily. Micturition diary and urodynamic variables and subjective urinary symptoms were assessed after 2 weeks of treatment. Patients were classified as "extensive" or "poor" metabolizers of tolterodine on the basis of serum levels of tolterodine.

RESULTS

A per-protocol analysis of efficacy in 262 patients showed dose-related improvements in micturition diary and urodynamic variables. A dosage of 4 mg twice daily was, however, associated with an increase in residual urinary volume. The incidence of adverse events (mainly mild or moderate antimuscarinic effects) was comparable between placebo and tolterodine dosages of 2 mg twice daily. No serious drug-related adverse events were observed, and tolterodine had no clinically significant impact on electrocardiographic or laboratory findings. Changes in urodynamic variables were found to be related to the sum of unbound serum concentrations of tolterodine and its major active 5-hydroxymethyl metabolite. In poor and extensive metabolizers of tolterodine, exposure to the sum of these active moieties was similar, and the efficacy and safety profiles were comparable.

CONCLUSIONS

The results of this pooled data analysis indicate that tolterodine offers an effective treatment for patients with urinary symptoms attributable to overactive bladder. The optimal dosage is 1 to 2 mg twice daily, irrespective of metabolic phenotype.

Comparative formation, distribution, and elimination kinetics of diphenylmethoxyacetic acid (a diphenhydramine metabolite) in maternal and fetal sheep

Deamination to diphenylmethoxyacetic acid (DPMA) is the major route of diphenhydramine (DPHM) clearance in many species. In this study, we assessed the contribution of this pathway to nonplacental DPHM elimination and disposition of DPMA in maternal and fetal sheep. Paired maternal-fetal experiments were conducted in five chronically catheterized pregnant sheep (124-140 days gestation) with an appropriate washout period in between. Both maternal and fetal dosing experiments involved administration of an i.v bolus of deuterium-labeled DPMA ([2H10]-DPMA) combined with a 6-h infusion of DPHM (or a bolus of unlabeled DPMA with an infusion of deuterium-labeled DPHM). Maternal and fetal arterial plasma and urine samples were collected and analyzed for DPMA, [2H10]-DPMA, DPHM, and deuterium-labeled DPHM concentrations using gas chromatography-mass spectrometry. The preformed DPMA (or [2H10]-DPMA) had a substantially lower clearance (maternal: 0.55 +/- 0.18 versus 40.9 +/- 14.0 ml/min/kg; fetal: 0.37 +/- 0.11 versus 285. 6 +/- 122.2 ml/min/kg) and steady-state volume of distribution (Vdss, maternal: 0.10 +/- 0.02 versus 2.1 +/- 1.1 l/kg; fetal: 0.40 +/- 0. 06 versus 13.1 +/- 3.1 l/kg) as compared with the parent drug. The contribution of DPMA formation to maternal and fetal DPHM nonplacental clearance in vivo was 1.78 +/- 2.12% and 0.87 +/- 0.56%, respectively, indicating that DPMA formation is not a major route of DPHM clearance in fetal or maternal sheep. The recoveries of DPMA (or [2H10]-DPMA) in maternal urine were 88.0 +/- 6.5 and 92.1 +/- 7. 4% of the administered dose during maternal and fetal dosing experiments, respectively. Thus, this metabolite does not appear to be secondarily metabolized in fetal or maternal sheep. These findings are in contrast to other species (dog, rhesus monkey, human) where DPMA and its conjugates constitute approximately 40 to 60% of the total DPHM metabolites.

Open-label, single-dose pharmacokinetic study of modafinil tablets: influence of age and gender in normal subjects

An open-label, single-center, single-dose, parallel-group study was performed in healthy young males and females as well as healthy elderly males to examine the influence of age and gender on the pharmacokinetics of modafinil following administration of a single 200 mg oral dose. Twelve subjects were enrolled in each of the following three groups: young males, young females, and elderly males. Each fasted (overnight) subject received 2 x 100 mg modafinil tablets. Blood and urine samples were collected at various times up to 72 hours postdose for the determination of plasma and urine levels of modafinil as well as the acid and sulfone metabolites. The plasma concentrations of the individual isomers, d- and l-modafinil, were also determined. Pharmacokinetic parameters were determined by noncompartmental methods. Modafinil was well tolerated at a single oral dose of 200 mg. The most commonly reported adverse events were headache, fever, pharyngitis, and asthenia. There were no clinically meaningful differences with respect to the incidence rate of treatment-emergent adverse events among the young female, young male, and old male groups. Modafinil was rapidly absorbed after oral dosing and slowly cleared (t1/2 approximately 11-14 hr) from the body. Modafinil acid was the major urinary metabolite, which accounted for 35% to 60% of the dose. Results from this study indicated that there were age and gender effects on modafinil clearance processes. In this regard, the clearance rate of modafinil in males decreased with age while young females cleared modafinil at a faster rate than young males. Stereospecific pharmacokinetics of modafinil were also demonstrated. The d-modafinil was eliminated three times faster than the l-modafinil.

Tolterodine, a new antimuscarinic drug for treatment of bladder overactivity

Tolterodine is a nonsubtype selective antimuscarinic agent recently approved as therapy in patients with overactive bladder with symptoms of urinary frequency, urgency, or urge incontinence. It acts by muscarinic receptor blockade in the bladder wall and detrusor muscle. Despite short terminal disposition half-lives of 2-3 and 3-4 hours for tolterodine and its active 5-hydroxy metabolite, respectively, twice/day dosing is effective due to the drug's prolonged pharmacodynamic effects. Dosage adjustment is recommended in the presence of hepatic impairment and during concurrent therapy with drugs that inhibit cytochrome P450 2D6 and 3A4 isozymes. Tolterodine significantly reduces clinically relevant end points such as number of micturitions and number of incontinence episodes/day. In general, it is superior to placebo and equivalent to oxybutynin in this regard. As might be expected from its pharmacologic profile, the principal adverse effects of the drug are anticholinergic. In clinical trials, tolterodine was tolerated significantly better than oxybutynin. Its relative merits as a first- or second-line agent for patients intolerant of oxybutynin are unclear. Until pharmacoeconomic analyses are conducted that clearly justify use of this more expensive agent, tolterodine is perhaps best reserved for patients who are intolerant of or fail oxybutynin therapy.

A double-blind, placebo-controlled, ascending-dose evaluation of the pharmacokinetics and tolerability of modafinil tablets in healthy male volunteers

A randomized, double-blind, placebo-controlled, ascending-dose study was conducted to evaluate the pharmacokinetic and safety profiles of increasing modafinil doses (200 mg, 400 mg, 600 mg, 800 mg) administered orally over a 7-day period in normal healthy male volunteers. Eight subjects (six modafinil; two placebo) were randomized to each of the four dose groups. Modafinil or a placebo was administered once daily for 7 days. Serial blood samples were obtained following administration of the day 1 and day 7 doses for characterization of pharmacokinetics, and trough samples were obtained prior to dosing on days 2 through 6 to assess the time to reach the steady state. Pharmacokinetic parameters were calculated using noncompartmental methods. Modafinil steady state was reached after three daily doses. Modafinil pharmacokinetics were dose and time independent over the range of 200 mg to 800 mg. Steady-state pharmacokinetics of modafinil were characterized by a rapid oral absorption rate, a low plasma clearance of approximately 50 mL/min, a volume of distribution of approximately 0.8 L/kg, and a long half-life of approximately 15 hr. Modafinil was primarily eliminated by metabolism. Modafinil acid was the major urinary metabolite. Stereospecific pharmacokinetics of modafinil were demonstrated. The d-modafinil enantiomer was eliminated at a threefold faster rate than 1-modafinil. Modafinil 200 mg, 400 mg, and 600 mg doses were generally well tolerated. The modafinil 800 mg dose panel was discontinued after 3 days of treatment due to the observation of increased blood pressure and pulse rate. The safety data from this study suggest that the maximum tolerable single daily oral modafinil dose, without titration, may be 600 mg.

Comparison of the single-dose pharmacokinetics and tolerability of modafinil and dextroamphetamine administered alone or in combination in healthy male volunteers

An open-label, randomized, crossover study was performed in healthy male volunteers to evaluate the potential pharmacokinetic and pharmacodynamic interactions and tolerability of single oral doses of modafinil (200 mg) and dextroamphetamine (10 mg). Blood samples were collected for determination of plasma levels of modafinil, the acid and sulfone metabolites of modafinil, and dextroamphetamine at intervals through 48 hours after administration for each treatment. Vital signs (blood pressure and pulse rate) were measured through 48 hours, and electrocardiograms were measured through 24 hours after administration. Pharmacokinetic parameters were determined using noncompartmental methods. The data collected in this study of 24 healthy volunteers suggest that concomitant administration of single oral doses of modafinil and dextroamphetamine has no clinically significant effects on the pharmacokinetic profile of either agent. Although there was a slightly greater incidence of adverse events when modafinil and dextroamphetamine were administered together, the concomitant administration of the two drugs was well tolerated.

Tolterodine

Tolterodine is a competitive muscarinic receptor antagonist which has recently been launched for the treatment of overactive bladder. Tolterodine shows functional selectivity for the bladder over the salivary glands in vivo, which is not attributable to muscarinic receptor subtype selectivity. It is as potent as oxybutynin in inhibiting bladder contraction, but is much less potent in inhibiting salivation, suggesting that it may have less propensity to cause dry mouth in clinical use. In patients with overactive bladder, toleterodine significantly reduces the frequency of micturition and number of incontinence episodes, while increasing the average volume voided. The onset of pharmacological action of tolterodine is < 1 hour and therapeutic efficacy is maintained during long term treatment. In comparative trials, tolterodine and oxybutynin are equivalent in terms of efficacy. However, tolterodine is significantly better tolerated than oxybutynin, particularly with respect to the incidence and severity of dry mouth. No clinically relevant ECG changes have been noted with tolterodine.

Biotransformation of tolterodine, a new muscarinic receptor antagonist, in mice, rats, and dogs

Tolterodine is a new muscarinic receptor antagonist intended for the treatment of urinary urge incontinence and other symptoms associated with an overactive bladder. The in vivo metabolism of 14C-labeled tolterodine was investigated in rats, mice, and dogs by analysis of blood and urine samples, whereas in vitro metabolism studies were performed by incubation of [14C]tolterodine with mouse, rat, dog, and human liver microsomes in the presence of NADPH. Tolterodine was extensively metabolized in vivo. Mice and dogs showed similar metabolite patterns, which correlated well with that observed in humans. In these species, tolterodine was metabolized along two different pathways, with the more important being the stepwise oxidation of the 5-methyl group to yield the 5-hydroxymethyl metabolite of tolterodine and then, via the aldehyde, the 5-carboxylic acid metabolite. The other pathway involved dealkylation of the nitrogen. In the subsequent phase II metabolism, tolterodine and the metabolites were conjugated with glucuronic acid to various degrees. Rats exhibited more extensive metabolism and a markedly different metabolite pattern, with metabolites also being formed by hydroxylation of the unsubstituted benzene ring. In addition, a gender difference was observed, with male rats showing more extensive metabolism than females. Incubation of [14C]tolterodine with liver microsomes yielded a total of five metabolites with rat liver microsomes and three with mouse, dog, and human liver microsomes. The 5-hydroxymethyl metabolite of tolterodine and N-dealkylated tolterodine were major metabolites in all incubations, representing 83-99% of total metabolism. Although the extent of metabolism varied among species, the metabolic profiles were similar. However, rat liver microsomes also formed metabolites hydroxylated in the unsubstituted benzene ring. These results show that the metabolism of tolterodine in mice and dogs corresponds to that observed in humans, whereas rats exhibit a different metabolite pattern.

Influence of CYP2D6 polymorphism on the pharmacokinetics and pharmacodynamic of tolterodine

OBJECTIVE

To determine whether cytochrome P450 2D6 (CYP2D6) is involved in the metabolism of tolterodine by investigating potential differences in pharmacokinetics and pharmacodynamic (heart rate, accommodation, and salivation) of tolterodine and its 5-hydroxymethyl metabolite between poor metabolizers and extensive metabolizers of debrisoquin (INN, debrisoquine).

METHODS

Sixteen male subjects (eight extensive metabolizers and eight poor metabolizers) received 4 mg tolterodine by mouth twice a day for 8 days followed by a single intravenous infusion of 1.8 mg tolterodine for 30 minutes after a washout period. Doses were given as the tartrate salt. The pharmacokinetics of tolterodine and 5-hydroxymethyl metabolite were determined, and the pharmacodynamic were measured.

RESULTS

The mean systemic clearance of tolterodine was significantly lower (p < 0.001) among poor metabolizers (9.0 +/- 2.1 l/hr) compared with extensive metabolizers (44 +/- 13 L/hr), resulting in a fourfold longer elimination half-life (p < 0.001). The terminal half-life of the 5-hydroxymethyl metabolite (2.9 +/- 0.4 hours) was slightly longer than that of the parent compound (2.3 +/- 0.6 hours) among extensive metabolizers, but the 5-hydroxymethyl metabolite was undetectable in the serum of poor metabolizers. Only minor differences in pharmacodynamic effects after tolterodine dosage were observed between the groups. Tolterodine caused a similar decrease in salivation in both panels. The decrease occurred when the concentration of unbound tolterodine and 5-hydroxymethyl metabolite among extensive metabolizers was comparable with that of tolterodine among poor metabolizers.

CONCLUSIONS

Tolterodine is extensively metabolized by CYP2D6 with high specificity. Despite the effect on pharmacokinetics, the CYP2D6 polymorphism does not appear to be of great importance in the antimuscarinic effect, probably because of the additive action of parent drug and active metabolite.

High-performance liquid chromatographic determination of modafinil and its two metabolites in human plasma using solid-phase extraction

A simple procedure for the simultaneous determination of modafinil, its acid and sulfone metabolites in plasma is described. The assay involved an extraction of the drug, metabolites and internal standard from plasma with a solid-phase extraction using C18 cartridges. These compounds were eluted by methanol. The extract was evaporated to dryness at 40 degrees C under a gentle stream of nitrogen. The residue was redissolved in 250 microl of mobile-phase and a 30 microl aliquot was injected via an automatic sampler into the liquid chromatograph and eluted with the mobile-phase (26%, v/v acetonitrile in 0.05 M orthophosphoric acid buffer adjusted to pH 2.6) at a flow-rate of 1.1 ml/min on a C8 Symmetry cartridge column (5 microm, 150 mm x 3.9 mm, Waters) at 25 degrees C. The eluate was detected at 225 nm. Intra-day coefficients of variation ranged from 1.0 to 2.9% and inter-day coefficients from 0.9 to 6.1%. The limits of detection and quantitation of the assay were 0.01 microg/ml and 0.10 microg/ml respectively.

Single-dose pharmacokinetics of modafinil and methylphenidate given alone or in combination in healthy male volunteers

Modafinil is a novel wake-promoting agent being developed for treatment of excessive daytime sleepiness associated with narcolepsy. An open, 3 x 3 Latin square, randomized, cross-over study was performed in healthy males to compare the pharmacokinetics of single-dose oral modafinil (200 mg) and methylphenidate (40 mg) administered alone or in combination. Blood samples were obtained for analysis of d- and l-threo-methylphenidate and modafinil and its acid and sulfone metabolites. Pharmacokinetic parameters were determined by noncompartmental methods, but could not be evaluated for modafinil sulfone due to plasma levels that were close to the assay quantitation limit. Although sporadic differences in plasma concentrations were observed between treatments, coadministration of modafinil and methylphenidate did not significantly alter the plasma concentrations of modafinil, modafinil acid, modafinil sulfone, or methylphenidate enantiomers compared with administration of these agents alone. Half-life (t1/2), maximum concentration (Cmax), area under the concentration-time curve (AUC0-infinity), total clearance (Cl/F), and apparent volume of distribution (Vd/F) for modafinil and t1/2, Cmax, and AUC0-infinity for modafinil acid were not affected by concomitant administration of methylphenidate. Small but statistically significant increases in time to Cmax (tmax) were observed for modafinil and modafinil acid after methylphenidate coadministration compared with modafinil alone. Modafinil coadministration did not significantly alter the pharmacokinetics of d- or l-threo-methylphenidate, except for a small decrease in Vd/F of l-threo-methylphenidate. Concomitant methylphenidate may cause a delay in the oral absorption of modafinil, but this delay might not be relevant clinically. Coadministration did not alter the extent of oral absorption and disposition of either agent. Therefore, a pharmacokinetic interaction between modafinil and methylphenidate would be unlikely.

In vitro and in vivo characterization of a calcium modulator of the diphenylalkylamine type with selective coronary dilatory properties

VUF 8929 (N-¿2-[bis(p-fluorophenyl)methoxy]ethyl¿-(2-phenyl)ethylamine maleate, CAS 140890-71-7) is a diphenylalkylamine derivative structurally related to prenylamine. The calcium antagonistic properties of this compound have been studied in in vitro and in vivo systems. VUF 8929 has affinity for the voltage-operated calcium channel. Its pKD for the displacement of [3H]nitrendipine bound to cerebral rat cortex is 6.27 (+/- 0.17). The compound influences the [3H]nitrendipine binding through an allosteric interaction with a site adjacent to the dihydropyridine binding site. Competitive experiments with the additional presence of the phenylalkylamine gallopamil showed that this allosteric site is a property common to diphenyl- and phenylalkylamines. It was further observed that VUF 8929 has a high affinity for calmodulin as it shows high potency in inhibiting the calmodulin mediated activation of PDE. The inhibition of K+ (IC50 0.5 mumol/l)- and noradrenaline (IC50 1.3 mumol/l)-induced contractions of rabbit aorta rings was in the same concentration range as found for the calmodulin inhibitory activity. In vitro platelet aggregation was also inhibited in the same concentration range when washed platelets were used. Thus calmodulin antagonism may contribute to the observed effects on aorta ring contractions and platelets aggregation. Platelet aggregation, however, in media in which albumin was added or in platelet rich plasma was not affected. It is assumed that due to the high lipophilicity, common to many diphenylalkylamines, VUF 8929 has a strong binding to plasma proteins. This may also explain why orally administered VUF 8929 did not affect the alpha 2-induced pressor response in pithed rats and the ex vivo collagen induced aggregation response. The haemodynamic profile in anaesthetized dogs showed that intravenous injected VUF 8929 reduced the workload of the heart while coronary blood flow increases at a dose of 0.3 mg/kg. Reversible occlusion of the coronary artery, which leads to S-T segment elevation and local venous acidosis, were reduced by VUF 8929 indicating that the compound has anti-ischaemic properties.

IN CONCLUSION

VUF 8929 is a calcium antagonist which has anti-ischaemic properties, reduces the workload of the heart and increases coronary flow. Due to these properties VUF 8929 is a potential cardioprotective agent.

Determination of tolterodine and the 5-hydroxymethyl metabolite in plasma, serum and urine using gas chromatography-mass spectrometry

A specific and sensitive capillary gas chromatography-mass spectrometry assay for the determination of tolterodine and the 5-hydroxymethyl metabolite (Labcode DD 01) in plasma, serum and urine is described. Extraction of the analytes was performed with liquid/liquid or solid-phase extraction prior to derivatisation with a silyl reagent. The derivatives were quantified by selected ion monitoring mass spectrometry using deuterium-labelled internal standards. A single level calibration curve was utilised for quantification of plasma, serum and urine concentrations of tolterodine and DD 01. The accuracy (inter- and intra-day) for both analytes was within 87-110% in the range 0.5 and 50 ng ml-1 and precision was better than 90%. Overall, this method was shown to be reliable for pharmacokinetic assays of tolterodine and the metabolite DD 01 in samples from preclinical and clinical studies.

Pharmacokinetics and pharmacodynamics of tolterodine in man: a new drug for the treatment of urinary bladder overactivity

The aim of this study was to determine the pharmacokinetics, pharmacodynamics, and safety of tolterodine following single oral and intravenous doses in healthy volunteers. A secondary aim was to identify major urinary metabolites and determine mass balance. Single oral doses of 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, and 12.8 mg of tolterodine (as the tartrate salt) were given to 17 healthy male volunteers. Two intravenous doses (0.64 and 1.28 mg) were administered to 8 of the volunteers and mass balance was studied after a single oral dose of 5 mg (14C)-tolterodine in 6 subjects. Tolterodine was rapidly absorbed following oral administration (time to peak serum concentration 0.9 +/- 0.4 h). The absolute bioavailability was highly variable, ranging from 10 to 70%. The volume of distribution at steady-state ranged from 0.9 to 1.6 l/kg and systemic clearance ranged from 0.23 to 0.52 l/h/kg, which resulted in a terminal half-life of 2-3 h. Tolterodine exhibited high first-pass metabolism and 2 hepatic metabolic pathways were identified: oxidation and dealkylation. Independent of route of administration, < 1% of the parent compound was excreted unchanged in urine. Five metabolites were structurally identified in urine. Following oral administration of (14C)-tolterodine, the excretion of radioactivity into urine and feces was 77 +/- 4.0% and 17 +/- 3.5%, respectively. Tolterodine decreased stimulated salivation after 3.2 mg, increased heart rate after 6.4 mg, and nearpoint of vision after 12.8 mg. Six of 8 subjects reported micturition difficulties after a dose of 12.8 mg. The lack of a direct relationship between tolterodine serum concentrations and effects on stimulated salivation suggested the presence of pharmacologically active metabolite(s).

Clinical pharmacokinetics and tolerability of dotarizine in healthy subjects after single and multiple oral administration

Dotarizine is a new diphenylmethylpiperazine derivative with Ca2+ channel blocking properties and inhibitory effects on 5-HT2A and 5-HT2C receptors. Previous pilot studies in healthy volunteers demonstrated a good tolerability after single and multiple dosing. Dotarizine appeared to be rapidly and extensively metabolized to an active compound (FI-6020). We aimed to study the physiologic, subjective and psychomotor acute effects of oral dotarizine after single dose administration, to evaluate the tolerability and safety after multiple dosing over 2 weeks, and to study the pharmacokinetic parameters and linearity after single and multiple administration. Two different studies were carried out in 2 groups of 8 healthy male volunteers. Oral single doses of dotarizine 50, 100 and 200 mg were administered in a randomized, double-blind, crossover, placebo-controlled trial. Oral doses of 50 mg twice daily were administered in an open trial over 14 days. Drug effect assessments included vital signs, collection of adverse events, ECG and blood and urine safety evaluations, subjective effects, psychomotor performance tasks and blood sampling. Dotarizine and its metabolite were determined by gas chromatography with N-P detector. The results showed a good tolerability of dotarizine after single oral doses as well as multiple oral doses over 14 days. No clinically relevant adverse events were reported during the study. The highest single dose (200 mg) produced a slight increase in sedation-related symptoms as well as a slight impairment in psychomotor performance tasks. Dotarizine and its major metabolite proved linear kinetics at single doses. The administration of oral doses of dotarizine 50 mg b.i.d. reached the steady state after the 7th day of treatment. The pharmacokinetic parameters remained similar from day 7 to day 14. The terminal elimination half-life of dotarizine and its metabolite appeared to be between 7 and 12 h.

Tolterodine--a new bladder selective muscarinic receptor antagonist: preclinical pharmacological and clinical data

Tolterodine is a new, potent and competitive muscarinic receptor antagonist in clinical development for the treatment of urge incontinence and other symptoms of unstable bladder. Tolterodine has a high affinity and specificity for muscarinic receptors in vitro and it exhibits a selectivity for the urinary bladder over salivary glands in vivo. A major active metabolite, (PNU-200577) the 5-hydroxymethyl derivative of tolterodine, has a similar pharmacological profile. Based on pharmacological and pharmacokinetic data, it has been concluded that this metabolite contributes significantly to the therapeutic effect of tolterodine. The bladder selectivity demonstrated by tolterodine and PNU-200577 in vivo cannot be attributed to selectivity for a single muscarinic receptor subtype. Moreover, this favourable tissue-selectivity seems to occur also in humans. Tolterodine is well tolerated and it exerts a marked effect on bladder function in healthy volunteers. Phase II data indicate that tolterodine is an efficacious and safe treatment for patients with idiopathic detrusor instability or detrusor hyperreflexia. An optimal efficacy/side-effect profile is obtained with tolterodine, at a dosage of 1 or 2 mg twice daily, which seems to have less propensity to cause dry mouth than the currently available antimuscarinic drugs.

Simultaneous analysis of diphenylmethoxyacetic acid, a metabolite of diphenhydramine, and its deuterium-labeled stable isotope analog in ovine plasma and urine

Diphenylmethoxyacetic acid (DPMA) is a major metabolite of diphenhydramine in monkeys, dogs, and humans. The metabolic fate of diphenhydramine (DPHM) in sheep is not yet well understood; however, preliminary studies have demonstrated the presence of DPMA in the plasma and urine of sheep following an intravenous bolus of DPHM. Our current studies employ the simultaneous intravenous co-administration of DPHM and the stable isotope analog of DPHM to investigate the pharmacokinetics of DPHM in sheep. In these studies, in order to investigate the pharmacokinetics of the DPMA metabolite, measurement of both unlabeled and stable-isotope labeled DPMA is required. Thus, a stable isotope analog of DPMA ([2H10]DPMA) was synthesized, characterized, and purified for use as an analytical standard. The quantitative method for the gas chromatography-electron-impact mass spectrometry (GC-EI-MS) analysis of DPMA and [2H10]DPMA used a single step liquid-liquid extraction procedure using toluene for sample cleanup. The samples were derivatized with N-methyl-N-(tert.-butyldimethylsilyl) trifluoroacetamide. A 1.0-microliter aliquot of the prepared sample was injected into the GC-MS system and quantitated using selected-ion monitoring (SIM). One ion was monitored for each compound, namely, m/z 165 for the internal standard diphenylacetic acid, m/z 183 for DPMA, and m/z 177 for [2H10]DPMA. The ion chromatograms were free from chromatographic peaks co-eluting with the compound of interest. The calibration curve was linear from 2.5 ng/ml (limit of quantitation) to 250.0 ng/ml in both urine and plasma. The intra-day and inter-day variabilities of this assay method were within acceptable limits (below 20% at the limit of quantitation and below 10% at all other concentrations). This method was used to measure the concentration of DPMA and [2H10]DPMA in plasma and urine samples from a ewe in which equimolar amounts of DPHM and [2H10]DPHM were administered by an intravenous bolus dose via the femoral vein. DPMA appeared to persist longer in the plasma and the urine as compared to DPHM. This method is robust and reliable for the quantitation of DPMA and [2H10]DPMA in biological samples obtained from sheep (e.g. plasma and urine).

Urodynamic and other effects of tolterodine: a novel antimuscarinic drug for the treatment of detrusor overactivity

Tolterodine, a novel compound intended for treatment of urgency and urge incontinence, has been characterized as a potent muscarinic receptor antagonist in pharmacological in vitro and in vivo studies. In cats, tolerodine was shown to reduce bladder pressure at doses significantly lower than those affecting salivation. To predict clinical effectiveness, an open pilot study was performed in healthy male volunteers. Efficacy was measured by cystometry and by spontaneously reported effects after administration of a single oral dose of tolterodine, 6.4 mg, given as a water solution. Tolterodine had distinct inhibitory effects on urinary bladder function, both at 1 and 5 hours post-dose. At 1 hour, but not at 5 hours post-dose tolterodine also significantly reduced stimulated salvation. In addition to the objectively demonstrated changes in urodynamic parameters, most volunteers experienced voiding difficulties. No significant changes in blood pressure, heart rate, or near point of accommodation were registered. Tolterodine, in the dosage used, was both objectively and subjectively shown to exert a marked inhibitory effect on micturition in healthy subjects, and the data suggest a more pronounced effect on bladder function than on salivation.

Inter-individual differences of 4-[4-(4-methylphenyl)-phenylmethoxy-1-piperidinyl]butyric acid disposition in rats: possible involvement of genetic polymorphism

Inter-individual differences of drug plasma concentration were recognized in outbred rats after an oral or intravenous administration of (+)-4-[4-(4-methylphenyl)phenylmethoxy-1-piperidinyl]butyric acid hydrochloride ((+)-MPPB). Rats could be divided into two phenotypes, the rapid metabolizing (RM) group and the slow metabolizing (SM) group. The hepatic clearance of RM-phenotyped Sprague-Dawley rats was about 10 times larger than that of the SM group. Outbred male and female Sprague-Dawley rats and male Wistar rats were mixtures of the RM and SM groups. On the other hand, all inbred male Lewis rats were RM, and all inbred male F344 and ACI rats were SM. This study was undertaken to investigate the inter-individual differences of (-)-MPPB and the metabolic pathways of (+)- and (-)-MPPB. When (-)-MPPB was orally administered to male Sprague-Dawley rats, similar inter-individual differences of plasma concentration were recognized. RM-phenotyped Sprague-Dawley rat liver microsomes metabolized (+)-MPPB to 4-hydroxymethylphenyl-MPPB (M1), and (-)-MPPB to M1 and 4'-hydroxyphenyl-MPPB (M2). The formation of these metabolites was less with SM-phenotyped than with RM-phenotyped Sprague-Dawley rat liver microsomes. The kinetic parameters of M1 formation from (+)-MPPB by RM-phenotyped rat liver microsomes were characteristic of a two-enzyme system with a 100-fold difference in their affinities (KM values). On the other hand, SM-phenotyped rats have only the low-affinity enzyme system. An inhibition study demonstrated that both enzymes were cytochrome P450.(ABSTRACT TRUNCATED AT 250 WORDS)