Prediction of alpha1-adrenoceptor occupancy in the human prostate from plasma concentrations of silodosin, tamsulosin and terazosin to treat urinary obstruction in benign prostatic hyperplasia

Efficacy and safety of silodosin in the treatment of lower urinary tract symptoms in elderly men taking antihypertensive medications

Background

Both hypertension and lower urinary tract symptoms (LUTS) are common conditions in the elderly population. This study investigated the efficacy and safety of silodosin in the treatment of LUTS in elderly men who were taking antihypertensive medications.

Methods

This is an observational study which collected the medical records of patients who started silodosin medication for their LUTS between April 2015 and December 2015. Inclusion criteria were age ≥ 65 years, currently taking antihypertensive medication, and International Prostate Symptom Score (IPSS) ≥ 8. Pretreatment evaluation included IPSS, Male Sexual Health Questionnaire, systemic symptoms, blood pressure, and uroflowmetry. Post-treatment evaluation was performed 3 months after the initial administration of silodosin medication.

Results

Mean age of the total 48 patients was 70.7 ± 5.2 years. Thirty-two (66.7%) patients who continued silodosin single treatment showed a significant decrease in IPSS Quality of life scores (4.2 ± 1.1 vs. 3.0 ± 1.6, P = 0.001) and an increase in the maximum flow rate (10.7 ± 6.0 mL/s vs. 14.0 ± 4.5 mL/s, P = 0.001). Blood pressures did not change, and none of the patients needed to adjust their antihypertensive medication. New development of orthostatic hypotension was observed in one (2.5%) patient. Among the six patients who had orthostatic hypotension before silodosin treatment, none of the patients showed symptom aggravation. Ejaculatory dysfunction that required discontinuation of silodosin medication developed in only one (2.5%) patient.

Conclusion

Silodosin is an effective and safe agent in elderly men who are taking antihypertensive medications. Silodosin has an advantage in the treatment of LUTS in this population, even if the patients have orthostatic hypotension before treatment.

Evaluation of silodosin in comparison to tamsulosin in benign prostatic hyperplasia: a randomized controlled trial

Objectives:

Benign prostatic hyperplasia (BPH) is the most common cause of lower urinary tract symptoms in elderly men. Selective alfa₁-adrenergic antagonists are now first-line drugs in the medical management of BPH. We conducted a single-blind, parallel group, randomized, controlled trial to compare the effectiveness and safety of the new alfa₁-blocker silodosin versus the established drug tamsulosin in symptomatic BPH.

Materials and Methods:

Ambulatory male BPH patients, aged above 50 years, were recruited on the basis of International Prostate Symptom Score (IPSS). Subjects were randomized in 1:1 ratio to receive either tamsulosin 0.4 mg controlled release or silodosin 8 mg once daily after dinner for 12 weeks. Primary outcome measure was reduction in IPSS. Proportion of subjects who achieved IPSS <8, change in prostate size as assessed by ultrasonography and changes in peak urine flow rate and allied uroflowmetry parameters, were secondary effectiveness variables. Treatment emergent adverse events were recorded.

Results:

Data of 53 subjects – 26 on silodosin and 27 on tamsulosin were analyzed. Final IPSS at 12-week was significantly less than baseline for both groups. However, groups remained comparable in terms of IPSS at all visits. There was a significant impact on sexual function (assessed by IPSS sexual function score) in silodosin arm compared with tamsulosin. Prostate size and uroflowmetry parameters did not change. Both treatments were well-tolerated. Retrograde ejaculation was encountered only with silodosin and postural hypotension only with tamsulosin.

Conclusions:

Silodosin is comparable to tamsulosin in the treatment of BPH in Indian men. However, retrograde ejaculation may be troublesome for sexually active patients.

Randomized Crossover Comparison of the Short-Term Efficacy and Safety of Single Half-Dose Silodosin and Tamsulosin Hydrochoride in Men With Lower Urinary Tract Symptoms Secondary to Benign Prostatic Hyperplasia

OBJECTIVE

To compare the efficacy and safety of single half-dose silodosin and single full-dose tamsulosin in Japanese men with lower urinary tract symptoms secondary to benign prostatic hyperplasia (LUTS/BPH).

METHODS

Japanese men aged ≥50 years with LUTS/BPH and an International Prostate Symptom Score (IPSS) of ≥8 were enrolled in the randomized crossover study and divided into silodosin-preceding (S-T) and tamsulosin-preceding (T-S) groups. The S-T group received 4 mg silodosin once daily for 4 weeks followed by 0.2 mg tamsulosin once daily for 4 weeks. The T-S group received the reverse treatment sequence. A washout period prior to drug crossover was not included. Subjective and objective efficacy parameters including IPSS, quality of life (QOL) index, uroflowmetry, and safety were compared between the two groups.

RESULTS

Thirty of 34 men (S-T group n = 16; T-S group n = 14) completed the study. Both drugs significantly improved all IPSS items and QOL index in the first treatment period. Subjective improvement in nocturia by silodosin was observed in both the first and crossover treatment periods. Objective improvement in maximum flow rate by silodosin was only observed in the first treatment period. Adverse events occurred more frequently with silodosin than with tamsulosin; however, none of the adverse events required treatment discontinuation. Ejaculation disorders occurred in three participants (10%) and were associated with silodosin use.

CONCLUSION

Single half-dose silodosin has a similar efficacy to full-dose tamsulosin in Japanese men with LUTS/BPH and thus, may represent an effective, safe, and affordable treatment option.

Safety and pharmacokinetic studies of silodosin, a new α1A-adrenoceptor selective antagonist, in healthy Chinese male subjects

The objectives of the study were to assess the safety and pharmacokinetics of silodosin capsules in 82 healthy male Chinese subjects. To evaluate the safety after single-dosing escalation, 40 subjects were equally divided into 4 groups (2, 4, 8, 12 mg) by a randomized, double-blind and placebo-controlled design. To assess the pharmacokinetics after single-dosing, 30 subjects were equally divided into 3 groups (4, 8, 12 mg). To assess the safety and pharmacokinetics via multiple-dosing, 12 subjects were included as a group (4 mg once daily at day 1 and day 7; 4 mg twice daily at day 2 through day 6). The safety observations showed that mild adverse events, including postural hypotension, dizziness, and headache, were observed. After single-dosing at doses of 4, 8, and 12 mg, the mean area under the concentration-time curve from 0 to 36 h (AUC(0-36)) values were 136.82±46.38, 270.17±54.66, and 474.63±108.50 µg/l·h and the mean maximal silodosin concentration in plasma (C(max)) values were 26.70±7.48, 48.47±12.35, and 94.07±22.59 µg/l, respectively. After multiple-dosing, the C(max) value at day 7 was 33.84±19.54 µg/l, and the AUC(0-24) value at day 7 was 193.19±68.96 µg/l·h. The accumulation ratio of the AUC value was 1.55 by comparing the multiple-dosing with the single-dosing. It is concluded that silodosin is safe and tolerated in healthy Chinese male subjects at the dosing levels used in this study. The mean C(max) and AUC values of silodosin increased proportionally with dose escalation, showing characteristics of linear pharmacokinetics.

The effect of plasma protein binding on in vivo efficacy: misconceptions in drug discovery

Data from in vitro plasma protein binding experiments that determine the fraction of protein-bound drug are frequently used in drug discovery to guide structure design and to prioritize compounds for in vivo studies. However, we consider that these practices are usually misleading, because in vivo efficacy is determined by the free (unbound) drug concentration surrounding the therapeutic target, not by the free drug fraction. These practices yield no enhancement of the in vivo free drug concentration. So, decisions based on free drug fraction could result in the wrong compounds being advanced through drug discovery programmes. This Perspective provides guidance on the application of plasma protein binding information in drug discovery.

Management of benign prostatic hyperplasia with silodosin

It has been reported that blockade of α1A-adrenoceptor (AR) relieves bladder outlet obstruction, while blockade of α1D-AR is believed to alleviate storage symptoms due to detrusor overactivity. Silodosin, (-)-1-(3-hydroxypropyl)-5-[(2R)-2-({2-[2-(2,2,2trifluoroethoxy) phenoxy]ethyl}amino)propyl]-2,3-dihydro-1H-indole-7- carboxamide, is a new α1A-AR selective antagonist. Silodosin is highly selective for the α1A-AR subtype, showing an affinity for the α1A-AR that is 583- and 55.5-fold higher than its affinity for the α1B-and α1D-ARs, respectively. In randomized, double-blind, placebo-controlled phase III studies performed in Japan and the United States, silodosin has been shown to be effective for both storage and voiding symptoms associated with benign prostatic hyperplasia. Early effects of silodosin (after 2-6 hours or day 1) on lower urinary tract symptoms have also been reported. In urodynamic studies, detrusor overactivity disappeared in 40% and improved in 35% of patients after administration. In pressure flow studies, the grade of obstruction on the International Continence Society nomogram showed improvement in 56% of patients. The rate of adverse events in the silodosin, tamsulosin and placebo groups was 88.6%, 82.3%, and 71.6%, respectively. The most common adverse event was (mostly mild) abnormal ejaculation (28.1%). However, few patients (2.8%) discontinued silodosin because of abnormal ejaculation. Orthostatic hypotension showed a similar incidence in the silodosin (2.6%) and placebo (1.5%) groups. In conclusion, silodosin improves detrusor overactivity and obstruction and thus may be effective for both storage and voiding symptoms in patients with benign prostatic hyperplasia.

Silodosin: an orally active selective α1-adrenoceptor antagonist for benign prostatic hyperplasia

α1-adrenoceptor antagonists play a central role in the treatment of uncomplicated symptomatic benign prostatic hyperplasia, frequently in combination with the 5-α-reductase inhibitors such as finasteride and dutasteride. Clinically useful examples include alfuzosin, doxazosin, tamsulosin and terazosin. These can be subdivided into nonselective (doxazosin and terazosin) and uroselective (alfuzosin and tamsulosin) agents. In general, these agents appear to be equieffective. However, they can be distinguished on the basis of their adverse event profiles. Such adverse events include those due to their vasodilatory effects (dizziness, orthostatic hypotension and rhinitis), genitourinary effects (ejaculatory dysfunction) and nonspecific effects (e.g., asthenia, malaise and gastrointestinal upset). A new α1A-adrenoceptor antagonist, silodosin, has recently been approved. In most ways, it is similar to tamsulosin in its pharmacodynamic effects in vitro and in vivo (in both animals and humans). Limited clinical trial data have shown silodosin to significantly improve lower urinary tract symptoms associated with benign prostatic hyperplasia and quality of life, with effects sustainable for at least 1 year. Its adverse-event profile reflects that seen with other uroselective α-adrenoceptor antagonists with the exception of a relatively high-incidence rate of ejaculatory dysfunction (22 vs 2% with tamsulosin and 28 vs 1% with placebo). This article reviews the preclinical and clinical data concerning silodosin and introduces the reader to this new drug for the treatment of benign prostatic hyperplasia.

Bladder angiotensin-II receptors: characterization and alteration in bladder outlet obstruction

BACKGROUND

It is assumed that angiotensin II (AngII) is significantly implicated in the pathogenesis of urinary dysfunction because of bladder outlet obstruction (BOO).

OBJECTIVE

The current study was undertaken to characterize AngII receptors in the rat bladder in relation to BOO.

MEASUREMENTS

Bladder AngII receptors were measured by a sensitive binding assay using a specific antagonist radioligand, [(125)I]-Sar(1)-Ile(8)-AngII, in bladder outlet-obstructed rats with and without repeated oral administration of telmisartan.

RESULTS AND LIMITATIONS

[(125)I]-Sar(1)-Ile(8)-AngII bound specifically to the rat bladder homogenates with high affinity. This specific binding of [(125)I]-Sar(1)-Ile(8)-AngII was concentration-dependently displaced by the type 1 subtype (AT(1))-selective antagonists. These findings revealed the significant existence of pharmacologically relevant AngII (AT(1)) receptors in the bladder with relatively high density. Oral administration of telmisartan in rats has been shown to bind to the bladder AngII receptors. Bladder weight was about three times greater in bladder outlet-obstructed rats than in sham rats. Maximal number of binding sites (B(max)) for [(125)I]-Sar(1)-Ile(8)-AngII binding in the bladder was significantly (48%) decreased in the bladder-outlet rats when compared with sham rats, suggesting the down regulation of pharmacologically relevant AngII receptor sites. Notably, repeated oral administration of telmisartan (3mg/kg/d, 14 d) in rats completely prevented the development of a BOO-induced decrease in B(max) for bladder [(125)I]-Sar(1)-Ile(8)-AngII binding. Telmisartan treatment also effectively attenuated the increase in the bladder-wet weight caused by urinary outlet obstruction.

CONCLUSIONS

Bladder AngII may be at least partly associated with the pathogenesis of urinary dysfunction occurring subsequent to BOO through stimulation of the AT(1) receptor subtype.