New perspectives on the overactive bladder: pharmacokinetics and bioavailability

On the Absolute Stereochemistry of Tolterodine: A Circular Dichroism Study

Tolterodine (1) is a potent muscarinic receptor antagonist used in the treatment of overactive urinary bladder (OAB) syndrome. Tolterodine is chiral and it was patented, and is currently marketed, as the l-tartrate salt of the (R)-enantiomer. However, the existing literature does not offer an ultimate proof of a stereoselective mode of action of 1. A second open stereochemical issue concerns the absolute configuration (AC) of 1. Neither the original patents nor subsequent studies have established the AC of 1 in an unambiguous way, although the AC of the l-tartrate salt of 1 was assigned by X-ray diffractometry. Finally, neither electronic nor vibrational circular dichroism (ECD and VCD) spectra of 1 are reported so far. We performed a thorough ECD/VCD study of 1 in different solvents and at variable temperatures. Solvent and temperature dependence highlighted the existence of moderate flexibility which was confirmed by molecular modelling. ECD calculations with time-dependent density functional theory (TDDFT) accurately reproduced the experimental spectra and allowed us to confirm the AC of 1 in an independent way.

Antimuscarinic drugs for the treatment of female urinary incontinence

Overactive bladder syndrome, urge syndrome or urgency-frequency syndrome is defined as 'urgency with or without urge incontinence, usually with frequency and nocturia'. Although this definition indicates that these symptoms are suggestive of detrusor overactivity (the observation of involuntary detrusor contractions during the filling phase of cystometry), a urodynamic demonstration of detrusor overactivity is not necessary in order to make the diagnosis. Nevertheless, patients with overactive bladder syndrome represent a substantial proportion of patients suffering with urinary symptomatology, and approximately a third of individuals with overactive bladder suffer from incontinence. Furthermore, as compared with those patients with stress urinary incontinence, women with urge incontinence have a poorer overall quality of life, perhaps related to both the volume of urine lost as well as the unpredictable nature of the leakage. When combined with behavioral modification, antimuscarinic pharmacotherapy remains the mainstay of treatment for this condition. A number of these agents are available for the treatment of overactive bladder-related incontinence, each with unique pharmacokinetic and pharmacodynamic properties. In order to optimize therapy for patients suffering from this type of incontinence, it is necessary to understand the mechanism of action of these agents, as well as to be familiar with the differences between them with respect to efficacy, safety and tolerability.

Carbamazepine toxicity following Oxybutynin and Dantrolene administration: a case report

OBJECTIVE

To report a case of Carbamazepine toxicity following the administration of Oxybutynin and Dantrolene.

STUDY DESIGN

A case report.

SETTING

The Spinal Rehabilitation Department, Loewenstein Hospital, Raanana, Israel.

METHODS

A patient with C6D tetraplegia who sustained intoxication because of drug interaction is presented. She had been treated by Carbamazepine 1000 mg/day for neuropathic pain for 2 years without clinical or laboratory signs of toxicity. After administration of Oxybutynin concomitantly with an increase in the dose of Dantrolene, she presented the clinical symptoms and laboratory finding of Carbamazepine intoxication. Trying to adjust the treatment to the patient's requirements, Carbamazepine together with Oxybutynin and Dantrolene was readministrated in lower doses.

RESULTS

The combination of these drugs, even small doses, caused toxicity. Adding Dantrolene and Oxybutynin elevated the blood level of Carbamazepine, possibly by inhibition of cytochrome P450.

CONCLUSION

A possible pharmacokinetic interaction between Dantrolene and Oxybutynin should be borne in mind when considering Carbamazepine medication for a patient with a spinal cord lesion.

Darifenacin, an M3 selective receptor antagonist, is an effective and well-tolerated once-daily treatment for overactive bladder

OBJECTIVES

To evaluate the efficacy, tolerability and safety of darifenacin, a once-daily M3) selective receptor antagonist (M3 SRA), in patients with overactive bladder (OAB).

METHODS

This multicentre, double-blind, placebo-controlled, parallel-group study enrolled 561 patients (19-88 years; 85% female) with OAB symptoms for >6 months, and included some patients with prior exposure to antimuscarinic agents. After washout and a 2-week placebo run-in, patients were randomised (1:4:2:3) to once-daily oral darifenacin controlled-release tablets (3.75 mg [n=53], 7.5 mg [229] or 15 mg [n=115]) or matching placebo (n=164) for 12 weeks. Patients recorded daily incontinence episodes, micturition frequency, bladder capacity (mean volume voided), frequency of urgency, severity of urgency, incontinence episodes resulting in change of clothing or pads and nocturnal awakenings due to OAB using an electronic diary during weeks 2, 6 and 12 (directly preceding clinic visits). Tolerability data were evaluated from adverse event reports.

RESULTS

Darifenacin 7.5 mg and 15 mg had a rapid onset of effect, with significant improvement compared with placebo being seen for most parameters at the first clinic visit (week 2). This effect was sustained through week 12. At this time the number of incontinence episodes per week was reduced from baseline by 67.7% with darifenacin 7.5 mg and 72.8% with darifenacin 15 mg compared with 55.9% with placebo (p=0.010 and p=0.017, respectively, versus placebo). The 3.75 mg group (null dose arm) was included for proof of concept of dose flexibility, therefore formal sample sizing and statistical analysis were not performed for this group. Darifenacin 7.5 mg and 15 mg, respectively, were significantly superior to placebo for improvements in micturition frequency (p<0.001, p<0.001), bladder capacity (p<0.040, p<0.001), frequency of urgency (p<0.001, p=0.005), severity of urgency (p<0.001, p=0.002) and number of incontinence episodes leading to a change in clothing or pads (p<0.001, p=0.002). There was no significant reduction in nocturnal awakenings due to OAB. The most common adverse events were mild-to-moderate dry mouth and constipation. However, no patients withdrew from the study as a result of dry mouth and discontinuation related to constipation was rare (0.6% placebo versus 0.9% darifenacin). In addition, there was a low need for laxative use, with no difference between the darifenacin groups and those taking placebo. There were no reports of blurred vision and the CNS and cardiac safety profile was comparable to placebo.

CONCLUSIONS

Darifenacin significantly improves the major symptoms of OAB. No significant CNS (primarily M1-receptor mediated) adverse events or cardiac (primarily M2-receptor mediated) adverse events were identified in this study, as may be predicted from the M3 selective receptor profile of darifenacin.