Tolterodine Tartrate

TOLTERODINE TARTRATE — tolterodine tartrate tablet, film coated
Camber Pharmaceuticals, Inc.

DESCRIPTION

Tolterodine tartrate tablets contain tolterodine tartrate. The active moiety, tolterodine, is a muscarinic receptor antagonist. The chemical name of tolterodine tartrate is 2-[(1R)-3-[Bis (1-methylethyl) amino]-1-phenylpropyl] — 4- Methyl phenol tartrate. The empirical formula of tolterodine tartrate is C ₂₂ H ₃₁ NO.C ₄ H ₆ O ₆ , and its molecular weight is 475.57. The structural formula of tolterodine tartrate is represented below:

Tolterodine tartrate USP is a white or almost white crystalline powder. The pKa value is 9.87. Sparingly soluble in water, slightly soluble in anhydrous ethanol, practically insoluble in heptane. Tolterodine tartrate tablets for oral administration contain 1 or 2 mg of tolterodine tartrate USP. The inactive ingredients are colloidal silicon dioxide, dibasic calcium phosphate dihydrate, hypromellose, magnesium stearate, microcrystalline cellulose, purified stearic acid, sodium starch glycolate and titanium dioxide. Additionally 1 mg tablet contains iron oxide yellow and iron oxide red.

CLINICAL PHARMACOLOGY

Tolterodine is a competitive muscarinic receptor antagonist. Both urinary bladder contraction and salivation are mediated via cholinergic muscarinic receptors.
After oral administration, tolterodine is metabolized in the liver, resulting in the formation of the 5-hydroxymethyl derivative, a major pharmacologically active metabolite. The 5-hydroxymethyl metabolite, which exhibits an antimuscarinic activity similar to that of tolterodine, contributes significantly to the therapeutic effect. Both tolterodine and the 5-hydroxymethyl metabolite exhibit a high specificity for muscarinic receptors, since both show negligible activity or affinity for other neurotransmitter receptors and other potential cellular targets, such as calcium channels.
Tolterodine has a pronounced effect on bladder function. Effects on urodynamic parameters before and 1 and 5 hours after a single 6.4 mg dose of tolterodine immediate release were determined in healthy volunteers. The main effects of tolterodine at 1 and 5 hours were an increase in residual urine, reflecting an incomplete emptying of the bladder, and a decrease in detrusor pressure. These findings are consistent with an antimuscarinic action on the lower urinary tract.

Pharmacokinetics

Absorption: In a study with ¹⁴ C-tolterodine solution in healthy volunteers who received a 5 mg oral dose, at least 77% of the radiolabeled dose was absorbed. Tolterodine immediate release is rapidly absorbed, and maximum serum concentrations (C _max ) typically occur within 1 to 2 hours after dose administration. C _max and area under the concentration-time curve (AUC) determined after dosage of tolterodine immediate release are dose-proportional over the range of 1 to 4 mg.
Effect of Food: Food intake increases the bioavailability of tolterodine (average increase 53%), but does not affect the levels of the 5-hydroxymethyl metabolite in extensive metabolizers. This change is not expected to be a safety concern and adjustment of dose is not needed.
Distribution: Tolterodine is highly bound to plasma proteins, primarily α ₁ -acid glycoprotein. Unbound concentrations of tolterodine average 3.7% ± 0.13% over the concentration range achieved in clinical studies. The 5-hydroxymethyl metabolite is not extensively protein bound, with unbound fraction concentrations averaging 36% ± 4.0 %. The blood to serum ratio of tolterodine and the 5-hydroxymethyl metabolite averages 0.6 and 0.8, respectively, indicating that these compounds do not distribute extensively into erythrocytes. The volume of distribution of tolterodine following administration of a 1.28 mg intravenous dose is 113 ± 26.7 L.
Metabolism: Tolterodine is extensively metabolized by the liver following oral dosing. The primary metabolic route involves the oxidation of the 5-methyl group and is mediated by the cytochrome P450 2D6 (CYP2D6) and leads to the formation of a pharmacologically active 5-hydroxymethyl metabolite. Further metabolism leads to formation of the 5-carboxylic acid and N -dealkylated 5-carboxylic acid metabolites, which account for 51% ± 14% and 29% ± 6.3% of the metabolites recovered in the urine, respectively.
Variability in Metabolism: A subset (about 7%) of the population is devoid of CYP2D6, the enzyme responsible for the formation of the 5-hydroxymethyl metabolite of tolterodine. The identified pathway of metabolism for these individuals (““poor metabolizers””) is dealkylation via cytochrome P450 3A4 (CYP3A4) to N -dealkylated tolterodine. The remainder of the population is referred to as “extensive metabolizers.” Pharmacokinetic studies revealed that tolterodine is metabolized at a slower rate in poor metabolizers than in extensive metabolizers; this results in significantly higher serum concentrations of tolterodine and in negligible concentrations of the 5-hydroxymethyl metabolite.
Excretion: Following administration of a 5 mg oral dose of ¹⁴ C-tolterodine solution to healthy volunteers, 77% of radioactivity was recovered in urine and 17% was recovered in feces in 7 days. Less than 1% (<2.5% in poor metabolizers) of the dose was recovered as intact tolterodine, and 5% to 14% (<1% in poor metabolizers) was recovered as the active 5-hydroxymethyl metabolite.
A summary of mean (± standard deviation) pharmacokinetic parameters of tolterodine immediate release and the 5-hydroxymethyl metabolite in extensive (EM) and poor (PM) metabolizers is provided in Table 1. These data were obtained following single and multiple doses of tolterodine 4 mg administered twice daily to 16 healthy male volunteers (8 EM, 8 PM). Table 1. Summary of Mean (±SD) Pharmacokinetic Parameters of Tolterodine and its Active Metabolite (5- hydroxymethyl metabolite) in Healthy Volunteers

* Parameter was dose-normalized from 4 mg to 2 mg.
C _max = Maximum plasma concentration; t _max = Time of occurrence of C _max ;
C _avg = Average plasma concentration; t _1/2 = Terminal elimination half-life; CL/F = Apparent oral clearance.
EM = Extensive metabolizers; PM = Poor metabolizers.
† †= not applicable.

Pharmacokinetics in Special Populations

Age: In Phase 1, multiple-dose studies in which tolterodine immediate release 4 mg (2 mg bid) was administered, serum concentrations of tolterodine and of the 5-hydroxymethyl metabolite were similar in healthy elderly volunteers (aged 64 through 80 years) and healthy young volunteers (aged less than 40 years). In another Phase 1 study, elderly volunteers (aged 71 through 81 years) were given tolterodine immediate release 2 or 4 mg (1 or 2 mg bid). Mean serum concentrations of tolterodine and the 5-hydroxymethyl metabolite in these elderly volunteers were approximately 20% and 50% higher, respectively, than reported in young healthy volunteers. However, no overall differences were observed in safety between older and younger patients on tolterodine in Phase 3, 12-week, controlled clinical studies; therefore, no tolterodine dosage adjustment for elderly patients is recommended (see PRECAUTIONS, Geriatric Use).
Pediatric: The pharmacokinetics of tolterodine have not been established in pediatric patients.
Gender: The pharmacokinetics of tolterodine immediate release and the 5-hydroxymethyl metabolite are not influenced by gender. Mean C _max of tolterodine (1.6 mcg/L in males versus 2.2 mcg/L in females) and the active 5-hydroxymethyl metabolite (2.2 mcg/L in males versus 2.5 mcg/L in females) are similar in males and females who were administered tolterodine immediate release 2 mg. Mean AUC values of tolterodine (6.7 mcg••h/L in males versus 7.8 mcg•••h/L in females) and the 5-hydroxymethyl metabolite (10 mcg•••h/L in males versus 11 mcg•••h/L in females) are also similar. The elimination half-life of tolterodine for both males and females is 2.4 hours, and the half-life of the 5-hydroxymethyl metabolite is 3 hours in females and 3.3 hours in males.
Race: Pharmacokinetic differences due to race have not been established.
Renal Insufficiency: Renal impairment can significantly alter the disposition of tolterodine immediate release and its metabolites. In a study conducted in patients with creatinine clearance between 10 and 30 mL/min, tolterodine immediate release and the 5-hydroxymethyl metabolite levels were approximately 2 to 3 fold higher in patients with renal impairment than in healthy volunteers. Exposure levels of other metabolites of tolterodine (e.g., tolterodine acid, N -dealkylated tolterodine acid, N -dealkylated tolterodine, and N -dealkylated hydroxylated tolterodine) were significantly higher (10 to 30 fold) in renally impaired patients as compared to the healthy volunteers. The recommended dosage for patients with significantly reduced renal function is tolterodine tartrate tablets 1 mg twice daily (see PRECAUTIONS, General and DOSAGE AND ADMINISTRATION).
Hepatic Insufficiency: Liver impairment can significantly alter the disposition of tolterodine immediate release. In a study conducted in cirrhotic patients, the elimination half-life of tolterodine immediate release was longer in cirrhotic patients (mean, 7.8 hours) than in healthy, young, and elderly volunteers (mean, 2 to 4 hours). The clearance of orally administered tolterodine was substantially lower in cirrhotic patients (1.0 ± 1.7 L/h/kg) than in the healthy volunteers (5.7 ± 3.8 L/h/kg). The recommended dose for patients with significantly reduced hepatic function is tolterodine tartrate tablets 1 mg twice daily (see PRECAUTIONS, General and DOSAGE AND ADMINISTRATION).