Tolterodine does not affect the human in vivo metabolism of the probe drugs caffeine, debrisoquine and omeprazole

Hansen solubility parameters and quality-by-design oriented optimized cationic nanoemulsion for transdermal drug delivery of tolterodine tartrate

Tolterodine tartrate (TOT) is a selective anti-muscarinic drug to treat urinary urgency and overactive urinary bladder (OAB) occurring in children, renal disease and elderly patients. Oral delivery is associated with several adverse effects. We addressed HSPiP and QbD (quality by design)-oriented TOT loaded cationic nanoemulsions for transdermal delivery. Hansen solubility parameters (HSP) screened excipients based on theoretical solubility whereas, QbD optimized cationic nanoemulsions (CNE-TOT-6). Formulation characteristic parameters were desirable to execute targeted in vitro drug release and ex vivo permeation profiles. In vitro hemolysis was conducted at varied concentrations whereas, histopathological study supported the safety aspect of CNE-TOT6. A comparative bioavailability was carried out in a rat model. Capmul PG8 (CAP), tween 80, and PEG 400 (polyethylene glycol 400) were screened based on HSP and experimental solubility data. QbD suggested optimized content of CAP, tween 80, and PEG 400 to achieve the lowest value of size (184 nm), maximum % entrapment efficiency (87.2 %), high zeta potential (+32.6 mV), optimum viscosity (47.19 cP), and high extrudability (96 %) as compared to its gel. High gel consistency slowed down the drug release and permeation flux as compared to CNE-TOT6 suspension. Hemocompatible CNE-TOT6 increased pharmacokinetic parameters as compared to the control and gel without causing skin toxicity after application. Thus, HSPiP and QbD oriented cationic nanoemulsions are promising carriers to treat overactive urinary bladder.

Use of Cocktail Probe Drugs for Indexing Cytochrome P450 Enzymes in Clinical Pharmacology Studies - Review of Case Studies

BACKGROUND

The cocktail approach of probing drug metabolizing enzymes, in particular cytochrome P450 (CYP) enzymes, is a cornerstone in clinical pharmacology studies. The first report of the famous "Pittsburg cocktail" has led the way for the availability of numerous cocktail substrate mixtures that provide options for indexing of CYP enzymes and/or evaluating the perpetrator capacity of the drug.

OBJECTIVE

The key objectives were: 1) To collate, tabulate, and discuss the various cocktail substrates to determine specific CYP enzyme activity in clinical pharmacology studies with specific case studies; 2) To introspect on how the cocktail approach has withstood the test of time and evolved for enabling key decision(s); 3) To provide some futuristic views on the use of cocktail in drug discovery and development.

METHOD

The review was compiled after consultation with databases such as PubMed (NCBI database) and Google scholar to source various published literature on cocktail approaches in drug development.

RESULTS

In the reviewed case studies, CYP indexing was achieved using a single time point (differing for specific CYP enzyme) plasma determination of the metabolite to parent ratio for all CYP enzymes with the exception of CYP3A4/5, where multiple time points were required for exposure measurement of midazolam and its metabolite. Likewise, a single void of urine, for a specific time duration, has been utilized for the recovery measurements of parent and metabolite for CYP indexing purposes.

CONCLUSION

The review provides a comprehensive list of various types of cocktail approaches and discusses some key considerations including the evolution of the cocktail approaches over time, perspectives and futuristic views for the use of probe drugs to aid the execution of clinical pharmacology studies and data interpretation.

Pharmacokinetic drug interaction study between overactive bladder drugs mirabegron and tolterodine in Japanese healthy postmenopausal females

Mirabegron, the first selective β₃-adrenoceptor agonist for the treatment of overactive bladder (OAB), inhibits cytochrome P450 isozyme CYP2D6. This study was performed in Japanese healthy postmenopausal female volunteers to assess any pharmacokinetic drug interaction between mirabegron and tolterodine, another OAB drug and a sensitive substrate of CYP2D6. Tolterodine 4 mg was orally administered from Days 1-7 and co-administered with mirabegron 50 mg from Days 8-14. Mirabegron 50 mg increased maximum concentration (C_max) and area under the concentration-time curve from zero to 24 h after dosing (AUC_24h) of tolterodine by 2.06-fold (90% confidence interval [CI] 1.81, 2.34) and 1.86-fold (90% CI 1.60, 2.16), respectively, and increased C_max and AUC_24h of the metabolite 5-hydroxymethyl tolterodine by 1.36-fold (90% CI 1.26, 1.47) and 1.25-fold (90% CI 1.15, 1.37), respectively. This suggested a weak pharmacokinetic drug interaction between mirabegron and tolterodine. Mean change from baseline of Fridericia's QT correction formula (ΔQTcF) was slightly higher on Day 14 than on Day 7. No subject had QTcF >480 msec or ΔQTcF >60 msec. All the treatment-emergent adverse events were mild. Mirabegron 50 mg was considered to be safe and well tolerated when coadministered with tolterodine 4 mg in healthy postmenopausal female volunteers.

Inhibition of metoprolol metabolism and potentiation of its effects by paroxetine in routinely treated patients with acute myocardial infarction (AMI)

OBJECTIVE

To investigate the influence of paroxetine on metoprolol concentrations and its effect in patients treated for acute myocardial infarction (AMI) who are routinely given paroxetine as a co-treatment of depression.

METHODS

We recruited 17 depressed AMI patients who received metoprolol as a routine part of their therapy (mean dose 75 +/- 39 mg/day). Patients were genotyped for CYP2D6 3, 4 and gene duplication. Metoprolol and alpha-hydroxy-metoprolol were analyzed in plasma 0, 2, 6 and 12 h post-dose. Heart rates (HR) at rest were registered after each sampling. Paroxetine 20 mg daily was then administered, and all measurements were repeated on day 8.

RESULTS

All patients were genotypically extensive metabolizers (EMs) (nine with 1/1 and eight with 1/3 or 4). Following the administration of paroxetine, mean metoprolol areas under the concentration-time curve (AUC) increased (1064 +/- 1213 to 4476 +/- 2821 nM x h/mg per kg, P = 0.0001), while metabolite AUCs decreased (1492 +/- 872 to 348 +/- 279 n M x h/mg per kg, P < 0.0001), with an increase of metabolic ratios (MR) (0.9 +/- 1.3 to 26 +/- 29; P < 0.0001). Mean HRs were significantly lower after the study week at each time point. Mean area under the HR versus time curve (AUEC) decreased (835 +/- 88 to 728 +/- 84 beats x h/min; P = 0.0007). Metoprolol AUCs correlated with patients' AUECs at the baseline (Spearman r = -0.64, P < 0.01), but not on the eighth day of the study. A reduction of metoprolol dose was required in two patients due to excessive bradycardia and severe orthostatic hypotension. No other adverse effects of the drugs were identified.

CONCLUSION

A pronounced inhibition of metoprolol metabolism by paroxetine was observed in AMI patients, but without serious adverse effects. We suggest, however, that the metoprolol dose is controlled upon initiation and withdrawal of paroxetine.

Pharmacogenetics, drug-metabolizing enzymes, and clinical practice

The application of pharmacogenetics holds great promise for individualized therapy. However, it has little clinical reality at present, despite many claims. The main problem is that the evidence base supporting genetic testing before therapy is weak. The pharmacology of the drugs subject to inherited variability in metabolism is often complex. Few have simple or single pathways of elimination. Some have active metabolites or enantiomers with different activities and pathways of elimination. Drug dosing is likely to be influenced only if the aggregate molar activity of all active moieties at the site of action is predictably affected by genotype or phenotype. Variation in drug concentration must be significant enough to provide "signal" over and above normal variation, and there must be a genuine concentration-effect relationship. The therapeutic index of the drug will also influence test utility. After considering all of these factors, the benefits of prospective testing need to be weighed against the costs and against other endpoints of effect. It is not surprising that few drugs satisfy these requirements. Drugs (and enzymes) for which there is a reasonable evidence base supporting genotyping or phenotyping include suxamethonium/mivacurium (butyrylcholinesterase), and azathioprine/6-mercaptopurine (thiopurine methyltransferase). Drugs for which there is a potential case for prospective testing include warfarin (CYP2C9), perhexiline (CYP2D6), and perhaps the proton pump inhibitors (CYP2C19). No other drugs have an evidence base that is sufficient to justify prospective testing at present, although some warrant further evaluation. In this review we summarize the current evidence base for pharmacogenetics in relation to drug-metabolizing enzymes.

Effect of the proton pump inhibitor omeprazole on the pharmacokinetics of extended-release formulations of oxybutynin and tolterodine

This study assessed the effect of the proton pump inhibitor omeprazole on the bioavailability of the extended-release formulations of oxybutynin and tolterodine. Forty-four healthy volunteers received each of 4 treatments in a 4-period crossover design. The treatments consisted of osmotically controlled extended-release oxybutynin chloride tablets at 10 mg/d or extended-release tolterodine tartrate capsules at 4 mg/d, with and without preceding treatment with 20 mg omeprazole daily for 4 days. Blood samples collected predose and at scheduled time points for 36 hours postdose were analyzed for oxybutynin and its active metabolite, N-desethyloxybutynin, or tolterodine and its active 5-hydroxymethyl metabolite, as appropriate. The AUCinfinity ratios for oxybutynin and its metabolite with and without prior omeprazole fell within the 80% to 125% range (accepted as the criterion for bioequivalence), as did those for tolterodine and its active moiety. The peak concentration ratios for oxybutynin and metabolite also conformed to this range; those for tolterodine did not. Increasing gastric pH with omeprazole does not substantially alter the pharmacokinetic properties of extended-release oxybutynin but may alter those of extended-release tolterodine.

Use of omeprazole sulfone in a single plasma sample as a probe for CYP3A4

OBJECTIVE

The hydroxylation of omeprazole, measured as the ratio of omeprazole/5-hydroxyomeprazole in a plasma sample taken 3 h after an oral dose, is an established method to determine CYP2C19 activity, and the ratio of omeprazole AUC/omeprazole sulfone AUC has been used for assessing CYP3A4 activity. The aim of this study was to determine whether the latter ratio from a single 3-h sample can also be used for CYP3A4 phenotyping.

METHODS

Plasma levels of omeprazole and omeprazole sulfone were analyzed by reversed-phase high-performance liquid chromatography in a blood sample drawn 3 h after intake of a single oral 20-mg dose of omeprazole by 22 healthy subjects and five patients with newly diagnosed epilepsy. The procedure was repeated on the 4th day of 200 mg of ketoconazole intake (10 subjects), after 3 weeks of 150-200 mg twice-daily carbamazepine (five patients), and on the 6th day of 4 mg twice-daily tolterodine (12 subjects). Five subjects also took 100 mg and 50 mg of ketoconazole for 3 days before concomitant intake with omeprazole.

RESULTS

The mean log10(omeprazole/omeprazole sulfone) ratio was 0.18 3 h after intake of omeprazole alone. After concomitant intake of ketoconazole, the corresponding value was 1.38 (p<0.001); after intake of carbamazepine it was -0.42 (p<0.05); and after tolterodine it was 0.29 (not significant). In the five subjects taking increasing doses of ketoconazole, the ratio was 0.11, 0.79, 1.2, and 1.5 after 0, 50, 100, and 200 mg of ketoconazole, respectively. The correlation between the metabolic ratios from the AUC((0-6h)) and from the single 3-h samples was very good, with a correlation coefficient of 0.92 (p<0.001).

CONCLUSIONS

A single blood sample taken 3 h after intake of 20 mg of omeprazole can be reliably used to phenotype for both CYP2C19 and CYP3A4 activity.

Clinical pharmacokinetics of drugs used to treat urge incontinence

Urge incontinence (also known as overactive bladder) is a common form of urinary incontinence, occurring alone or as a component of mixed urinary incontinence, frequently together with stress incontinence. Because of the pathophysiology of urge incontinence, anticholinergic/antispasmodic agents form the cornerstone of therapy. Unfortunately, the pharmacological activity of these agents is not limited to the urinary tract, leading to systemic adverse effects that often promote nonadherence. Although the pharmacokinetics of flavoxate, propantheline, scopolamine, imipramine/desipramine, trospium chloride and propiverine are also reviewed here, only for oxybutynin and tolterodine are there adequate efficacy/tolerability data to support their use in urge incontinence. Oxybutynin is poorly absorbed orally (2-11% for the immediate-release tablet formulation). Controlled-release oral formulations significantly prolong the time to peak plasma concentration and reduce the degree of fluctuation around the average concentration. Significant absorption occurs after intravesical (bladder) and transdermal administration, although concentrations of the active N-desethyl metabolite are lower after transdermal compared with oral administration, possibly improving tolerability. Food has been found to significantly affect the absorption of one of the controlled-release formulations of oxybutynin, enhancing the rate of drug release. Oxybutynin is extensively metabolised, principally via N-demethylation mediated by the cytochrome P450 (CYP) 3A isozyme. The pharmacokinetics of tolterodine are dependent in large part on the pharmacogenomics of the CYP2D6 and 3A4 isozymes. In an unselected population, oral bioavailability of tolterodine ranges from 10% to 74% (mean 33%) whereas in CYP2D6 extensive metabolisers and poor metabolisers mean bioavailabilities are 26% and 91%, respectively. Tolterodine is metabolised via CYP2D6 to the active metabolite 5-hydroxymethyl-tolterodine and via CYP3A to N-dealkylated metabolites. Urinary excretion of parent compound plays a minor role in drug disposition. Drug effect is based upon the unbound concentration of the so-called 'active moiety' (sum of tolterodine + 5-hydroxymethyl-tolterodine). Terminal disposition half-lives of tolterodine and 5-hydroxymethyl-tolterodine (in CYP2D6 extensive metabolisers) are 2-3 and 3-4 hours, respectively. Coadministration of antacid essentially converts the extended-release formulation into an immediate-release formulation. Knowledge of the pharmacokinetics of these agents may improve the treatment of urge incontinence by allowing the identification of individuals at high risk for toxicity with 'usual' dosages. In addition, the use of alternative formulations (controlled-release oral, transdermal) may also facilitate adherence, not only by reducing the frequency of drug administration but also by enhancing tolerability by altering the proportions of parent compound and active metabolite in the blood.

Benefit-Risk Assessment of Tolterodine in the Treatment of Overactive Bladder in Adults

Overactive bladder is associated with symptoms of urgency, with or without urge incontinence, usually with daytime frequency and nocturia in the absence of local pathological factors. Muscarinic receptor antagonists (antimuscarinics) are the first-line pharmacotherapy. Tolterodine, a competitive, nonselective antimuscarinic specifically developed for the treatment of overactive bladder, demonstrated tissue selectivity for the bladder over the parotid gland in an animal model. As of March 5, 2003, the immediate-release (IR) formulation had been approved in 72 countries and the extended-release (ER) formulation had been approved in 28 countries, and tolterodine had been administered to 5 million patients. This review evaluates the benefit-risk profile of tolterodine in the treatment of adults with overactive bladder, summarising clinical trial and postmarketing surveillance data. Tolterodine has been found to significantly reduce micturition frequency, urgency perception and the number of episodes of urge incontinence and increase the volume voided per micturition. Dry mouth, an antimuscarinic class effect, is the most commonly reported adverse effect but is mostly mild to moderate in severity. Serious adverse effects are reported infrequently. Based on summary and review of postmarketing surveillance and clinical trial safety data received by the market authorization holder and contained in the Periodic Safety Update Reports for tolterodine, several monitored serious events of the gastrointestinal tract (e.g. ileus or haemorrhage), nervous system (e.g. syncope, convulsions and memory disorders) and cardiovascular system (e.g. ventricular arrhythmia, atrial fibrillation, palpitations, bradycardia, transient ischaemic attacks and hypertension) were not considered related to tolterodine. QT or corrected QT (QTc) prolongation was not observed in any of the five cases of verified ventricular arrhythmia in patients administered tolterodine; there is insufficient evidence to indicate that tolterodine causes ventricular arrhythmia or extrasystoles or any specific type of cardiac rhythm abnormality. The safety profile of tolterodine is similar in patients aged > or =65 years and in younger adults. Clinically relevant drug interactions are limited to cytochrome P450 3A4 inhibitors, such as ketoconazole, and co-administration with such agents warrants a tolterodine dosage decrease. In addition, tolterodine IR 2mg twice daily is similar in efficacy to oxybutynin IR 5mg three times daily, and tolterodine ER 4 mg once daily is similar in efficacy to oxybutynin ER 10mg once daily. Dry mouth occurred less frequently with tolterodine than oxybutynin, and moderate to severe dry mouth occurred more than three times less frequently. Based on the low frequency of adverse events, the absence of unexpected adverse events and the very low frequency of serious adverse events, we conclude that tolterodine is a well tolerated treatment for overactive bladder in adults, in whom it should be considered as first-line therapy.

Interferon-beta treatment in patients with multiple sclerosis does not alter CYP2C19 or CYP2D6 activity

AIMS

To determine CYP2C19 and CYP2D6 activity in patients with multiple sclerosis (MS) before and during interferon (IFN)-beta treatment.

METHODS

CYP2C19 and CYP2D6 activities were assessed using the probe drugs mephenytoin and debrisoquine, respectively. Urinary mephenytoin (S/R) and debrisoquine (debrisoquine/hydroxy-debrisoquine) metabolic ratios (MR) were determined in 10 otherwise healthy Caucasian multiple sclerosis (MS) patients in the initial stage of the disease, prior to and 1 month after commencing treatment with IFN-beta (Avonex, Rebif or Betaferon). In addition, CYP2C19*2, CYP2C19*3, CYP2D6*3, CYP2D6*4, and CYP2D6*5 genotyping was performed.

RESULTS

There was no significant difference in the (S)/(R) mephenytoin ratio (mean difference 0.04; 95% CI -0.03, 0.11) or the debrisoquine MR (mean difference 0.29; 95% CI -0.44, 1.02) before and during regular IFN-beta treatment in extensive metabolizers (EM) (P = 0.5 and P = 0.4 for the respective probe drugs; n = 9 subjects). There were also no differences between the different IFN-beta treatments (P = 0.6 for the (S)/(R) mephenytoin ratio and P = 0.7 for the debrisoquine MR; anova; n = 10).

CONCLUSIONS

IFN-beta treatment did not affect the activity of CYP2C19 or CYP2D6. The results suggest that it is safe to administer CYP2C19 or CYP2D6 substrates, without dose adjustment, to patients treated with IFN-beta.

How useful is the "cocktail approach" for evaluating human hepatic drug metabolizing capacity using cytochrome P450 phenotyping probes in vivo?

Relatively selective in vivo substrate probes have been developed for several major CYP isoforms involved in oxidative drug metabolism. There are basically two in vivo methods for identifying the phenotype. One method, the selective (CYP-specific) phenotyping method, involves administering one single probe drug, whereas the other is a mixed phenotyping or "cocktail" method involving the simultaneous administration of multiple probe drugs, specific for the individual P450. At present, caffeine and chlorzoxazone are used most often as probe drugs for CYP1A2 and CYP2E1, respectively, but these are not necessarily the best probe drugs. Of the potential probe drugs for CYP2C9, CYP2C19, CYP2D6 and CYP3A4, none is really useful. Despite current limitations, the cocktail method for obtaining information about multiple CYP activities in a single experimental session is likely to be more widely used as a screening or phenotyping method for humans in the future.

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.

Tolterodine: a review of its use in the treatment of overactive bladder

Tolterodine is a competitive muscarinic receptor antagonist that shows in vivo selectivity for the bladder over the salivary glands compared with oxybutinin. Results of randomised double-blind placebo-controlled studies indicate that tolterodine 4 mg/day (administered as immediate-release tablets 2mg twice daily or extended-release capsules 4mg daily) is superior to placebo in improving micturition diary variables in patients with overactive bladder. Moreover, tolterodine 2mg twice daily is as effective as oxybutynin 5mg 3 times daily. Maximum treatment effects with both drugs occurred after 5 to 8 weeks of treatment and improvements were maintained during long term treatment for up to 24 months. In a pooled analysis of four 12-week studies, equivalent and significant reductions in micturition frequency (-2.3 and -2.0 vs -1.4, p < 0.001) and the incidence of urge incontinence episodes (-1.6 and -1.8 vs -1.1, p < 0.05) were reported for tolterodine 2mg twice daily and oxybutynin 5mg 3 times daily compared with placebo. Functional bladder capacity was also significantly increased. Improvements in patient perceptions of their urgency symptoms and of problems caused by their bladder condition were significantly greater during treatment with tolterodine than with placebo. Tolterodine was generally well tolerated in clinical trials of up to 24 months' duration. Dry mouth was the most frequent adverse event. The incidence (40 vs 78%, p < 0.001) and intensity of this event was lower with tolterodine 2mg twice daily than oxybutynin 5mg 3 times daily. Additionally, a 23% lower incidence of dry mouth was reported with once daily extended-release tolterodine capsules than with twice daily immediate-release tablets (p < 0.02). The incidence of adverse CNS events with tolterodine was low and similar to that of placebo. Tolterodine was well tolerated in elderly patients and no serious tolerability concerns were identified.

CONCLUSION

Tolterodine is the first antimuscarinic agent to specifically developed for the treatment of overactive bladder. The functional selectivity of tolterodine for the bladder translates into good efficacy and tolerability in patients, including the elderly, with overactive bladder. Tolterodine is as effective as oxybutynin in improving micturition diary variables but is associated with a significantly lower incidence and intensity of dry mouth. This favourable tolerability profile, together with sustained clinical efficacy during long term treatment, places tolterodine as valuable treatment for the symptoms of overactive bladder.